Study on potential filter materials for use as substrate in constructed wetlands to strengthen phosphorus treatment performance from swine wastewater

In that context, this research “ Study on potential filter materials for use as substrate in constructed wetland to strengthen phosphorus removal from swine wastew[r]

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY

NGUYEN THI THUONG

STUDY ON POTENTIAL FILTER

MATERIALS FOR USE AS SUBSTRATE IN CONSTRUCTED WETLAND

TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE

FROM SWINE WASTEWATER

MASTER'S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY

NGUYEN THI THUONG

STUDY ON POTENTIAL FILTER

MATERIALS FOR USE AS SUBSTRATE IN CONSTRUCTED WETLAND

TO STRENGTHEN PHOSPHORUS TREATMENT PERFORMANCE

FROM SWINE WASTEWATER

MAJOR: ENVIRONMENTAL ENGINEERING CODE: PILOT

SUPERVISORS

DR NGUYEN THI AN HANG ASSOC PROF DR SATO KEISUKE

DR VU NGOC DUY

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ACKNOWLEDGMENTS

First of all, I would like to express my heartfelt gratitude to my principal supervisor, Dr Nguyen Thi An Hang for giving me a chance to explore an exciting research field – the constructed wetlands, for always inspiring me She has spent plenty of time for teaching, explaining hard questions as well as sharing her own experiences in approaching and solving research problems Thanks to that, I was well equipped with essential knowledge and skills to fulfill my research I also express my deepest thanks to Assoc Prof Dr Sato Keisuke, who provided me a great guidance during my internship Besides teaching, providing knowledge and enthusiastic support, he always treated me tenderly likes my father In addition, he helped me not to be confused when I first arrived in Japan My special thanks go to Dr Vu Ngoc Duy, who gave me valuable supports in developing research methods, implementing experiments, and deepening my research

The second, I want to send my sincere thanks to VNU Vietnam Japan University (VJU), Ritsumeikan University (RITs), Shimadzu Corporation and Shigaraki Center for warm welcome and enthusiastic support during my internship in Japan Without their precious supports, I would not be able to complete this research Especially, I would like to convey my devoted appreciation to Prof Dr Jun Nakajima, Assoc Prof Dr Hiroyuki Katayama, for teaching and supporting me during my study at VJU

This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 105.99-2018.13, 2018, Asean Research Center (ARC) research grant of Vietnam National University, Hanoi (VNU), and Japan International Cooperation Agency (JICA)

Last but not least, my profound gratitude goes to my family for their spiritual supports during my thesis writing and my daily life as well This accomplishment would not have been possible without them

Hanoi, May 31th, 2019

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TABLE OF CONTENTS

ACKNOWLEDGMENTS i

TABLE OF CONTENTS ii

LIST OF TABLES iv

LIST OF FIGURES iv

LIST OF ABBREVIATIONS v

INTRODUCTION

CHAPTER LITERATURE REVIEW

1.1 Phosphorus (P) pollution and its consequences

1.2 Regulations related to P removal

1.3 Phosphorus treatment technologies 11

1.4 Constructed wetlands (CWs) system for wastewater decontamination 19

1.4.1 Definition 19

1.4.2 Classification 19

1.4.3 Application of CWs in wastewater treatment 23

1.4.4 Factors influencing the CWs treatment performance 25

1.4.5 Mechanisms of P removal in CWs 29

1.5 Removing P by substrates in CWs 31

1.6 Overview of research objects 33

1.6.1 Swine waste water 33

1.6.2 Ca-rich bivalve shell as the substrate in CWs 35

CHAPTER MATERIALS AND RESEARCH METHODOLOGY 41

2.1 Materials and equipment 41

2.2 Experiment setting up 45

2.2.1 Modification of materials 45

2.2.2 Characterization of the developed material 46

2.2.3 Adsorption experiments 49

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2.3 Analytical methods 53

2.3.1 Phosphorus analysis 53

2.3.2 Other parameters analysis 53

2.4 Data statistical analysis 53

CHAPTER RESULTS AND DISCUSSION 55

3.1 Screening of filter materials for use as substrate in CWs 55

3.1.1 Comparing potential materials based on P adsorption capacities 55

3.1.2 Comparing filter materials based on their permeability 57

3.1.3 Comparing filter materials based on their side effects 58

3.1.4 Selection of potential filter materials 62

3.2 Intensive investigation of the selected filter materials –white hard clam (WHC) 64

3.2.1 Identification of the optimal modification conditions of WHC 64

3.2.2 Physicochemical properties 66

3.2.3 Batch experiment 70

3.2.4 Column experiment 80

3.2.5 Comparing the P removal efficiency of modified white hard clam (WHC-M800) in the synthetic and real swine wastewater 82

3.3 The P treatment performance in the integrated CWs – adsorption system 83

CHAPER CONCLUSION AND RECOMMENDATION 88

4.1 CONCLUSION 88

4.2 RECOMMENDATION 89

REFERENCES 90

APPENDICES 108

Appendix 1: Visiting some CW systems during internship in Japan 108

Appendix 2: Preparing WHC as the substrate in CWs 109

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LIST OF TABLES

Table 1.1 Effluent discharge standards of different countries

Table 1.2 Phosphorus removal efficiencies of different methods 17

Table 1.3 Mechanism of phosphorus removal in constructed wetland system 30

Table 1.4 Some filter media used for P removal 32

Table 1.5 The main composition of swine wastewater after anaerobic digestion by biogas chamber 34

Table 1.6 The main chemical compositions of bivalve shells and limestone 37

Table 1.7 Some studies used bivalve shell for P removal 39

Table 3.1 Phosphorus adsorption capacity of different materials 57

Table 3.2 Permeability constant (K) of investigated materials 58

Table 3.3 The concentration of heavy metals released from materials 61

Table 3.4 Summary of the obtained scores for investigated materials Error! Bookmark not defined. Table 3.5 Effect of calcination temperature 65

Table 3.6 Effect of the calcination time 66

Table 3.7 Brunauer Emmett Teller (BET) analysis 67

Table 3.8 Elemental content of WHC 68

Table 3.9 Elemental content of WHC-M800 68

Table 3.10 Langmuir and Freundlich adsorption isotherm constants 78

Table 3.10 P adsorption capacity at different conditions 81

Table 3.11 Parameters of real post-biogas swine wastewater in Chuong My, Hanoi 83

Table 3.12 The phosphorus concentrations before and after treatment with horizontal flow lab-scale constructed wetlands 85

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LIST OF FIGURES

Figure 1: Thesis‘s outline

Figure 1.1 Eutrophication from phosphorus contamination

Figure 1.2 The treatment technologies for phosphorus removal 11

Figure 1.3 Metabolic pathways of PAO under aerobic and anaerobic conditions 15

Figure 1.4 The classification of CWs used in wastewater treatments 19

Figure 1.5 The schematic surface flow constructed wetland 20

Figure 1.6 The schematic vertical flow constructed wetland 21

Figure 1.7 The schematic horizontal flow constructed wetland 21

Figure 1.8 The schematic hybrid constructed wetland 22

Figure 1.9 Phosphorus cycle in constructed wetland 29

Figure 1.10 The main clam species in Vietnam 37

Figure 2.1 Images of investigated filter materials 41

Figure 2.2 The routine to Thai Binh shellfish Co., Ltd, Tien Hai Thai Binh 42

Figure 2.3 Procedure to prepare WHC as phosphorous adsorbent 43

Figure 2.4 The pig farm in Chuong My, Hanoi 44

Figure 2.5 Equipments used in this study 45

Figure 2.7 The experiment setting according to Darcy law 47

Figure 2.8 Procedure for determine of porosity 47

Figure 2.9 Small column adsorption test 51

Figure 2.10 Integrated CWs-adsorption systems 52

Figure 2.11 Calibration curve for phosphorus analysis 53

Figure 3.1 Comparison of P adsorption capacity of investigated filter materials 56

Figure 3.2 pH of post-adsorption solutions 59

Figure 3.3 Images of raw WHC and WHC modified at different temperatures 65

Figure 3.4 SEM observation for WHC 67

Figure 3.5 SEM observation for 67

Figure 3.6 EDX spectrum of WHC 68

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Figure 3.8 FTIR analysis for WHC 69

Figure 3.9 FTIR analysis for WHC WHC-M800 69

Figure 3.10 Effect of pH of WHC on phosphorus removal 71

Figure 3.11 Effect of pH of WHC-M800 on phosphorus removal 71

Figure 3.12 Effect of dosage of WHC on phosphorus removal 73

Figure 3.13 Effect of dosage of WHC-M800 on phosphorus removal 73

Figure 3.14 Effect of temperature of WHC on phosphorus removal 74

Figure 3.15 Effect of temperature WHC-M800 on phosphorus removal 74

Figure 3.16 The fitting of isotherm models to P adsorption onto WHC 77

Figure 3.17 The fitting of isotherm models to P adsorption onto WHC-M800 77

Figure 3.18 Linear form of adsorption isotherm following Langmuir of WHC 77

Figure 3.19 Linear form of adsorption isotherm following Freundlich of WHC 77

Figure 3.20 Linear form of adsorption isotherm following Langmuir of WHC-M800 78 Figure 3.21 Linear form of adsorption isotherm following Freundlich of WHC-M800 78

Figure 3.22 Kinetic test of WHC 79

Figure 3.23 Kinetic test of WHC-M800 79

Figure 3.24 Breakthrough curve of WHC-M800 for P removal under the different flowrate 81

Figure 3.25 Breakthrough curve of WHC-M800 for P removal under the different initial concentration 81

Figure 3.26 Breakthrough curve of WHC-M800 for P removal under the different weight of material 81

Figure 3.28 P adsorption capacity of WHC-M by real wastewater and synthetic wastewater 83

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LIST OF ABBREVIATIONS

BET Brunauer emmett teller

BOD Biological oxygen demand

COD Chemical oxygen demand

EBPR Enhanced biological phosphorus removal

EPA Environmental Protection Agency

FTIR Fourier transform infrared spectroscopy

HAP Hydroxyapatite

HLR Hydraulic loading rate

HRT Hydraulic retention time

MAP Magnesium ammonium phosphate hexahydrate

MBRs Membrane bioreactor

PAOs Polyphosphate accumulating organisms

RO Reverse osmosis

SEM Scanning electron microscopy

USEPA United States environmental protection agency

WHC White hard clam

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INTRODUCTION

Background

Swine breeding industry is an important part of agriculture sector in Vietnam In recent years, numerous large scales of pig farms have been developed to meet the pork demand in the market According to General Statistics Office of Vietnam (2018), the whole country has about 500,000 livestock households, over 29 million pig heads, 3.8 million tons of meat Also, as the pig producer, Vietnam is the biggest in ASEAN and the seventh biggest in the world The swine breeding industry has promoted the economic development as well as the GDP of the country

Despite the huge economic benefits, pig breeding industry makes many environmental problems, which negatively affect to human health and ecosystems That is because swine wastewater normally contains high concentration of nutrients, such as phosphorus (P) and nitrogen (N) that are main reasons for eutrophication (Wang et al., 2013)

Currently, the most common method for swine wastewater treatment is anaerobic digestion using biogas chamber However, according to several studies, the concentration of pollutants in the effluent after biogas treatment is still very high, exceeding the permitted discharge standards (National Institute of Animal Husbandry, 2015) Thus, further treatment is necessary to ensure the concentration of P in the effluent meets requirements (Ngo, 2013; Nguyen, 2016) Among several technologies utilized for swine wastewater treatment, constructed wetland has shown a promising technology

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In addition, Vietnam is a tropical country with the hot and humid climate, which is appropriate for the growth of plants and microorganisms in CWs Thus, CW is a potential wastewater treatment method and can replace or support other high-cost chemical and physiological technologies (Nguyen, 2015)

The main concern with the swine wastewater is high content of organic matter, nitrogen and phosphorus While CWs can remove organic matter, suspended solids and nitrogen efficiently, its removal efficiency of phosphorus is still low, unless special filter materials with high P sorption capacity are utilized (Almuktar et al., 2018) Therefore, in order to strengthen P removal from wastewater using CWs, it is necessary to identify the potential filter materials with high P binding capacity (Vohla et al., 2011)

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production As a result, a huge amount of solid waste can be generated, creating the environmental burden Besides, the large amount of agricultural and industrial by-products (okara, coal slag, steel slag) discharged from the food processing and fuel manufacturing… This is a great potential for the development of the constructed wetlands based on the indigenous materials

In brief, the use of special materials as filter media in CWs to intensify P removal was reported somewhere However, there are no studies in Vietnam using locally available, adsorptive natural materials (laterite, limestone, coral), industrial by-products (steel slag, coal slag, white hard clam) and agricultural by products (okara) for enhancing phosphorus removal efficacy from swine wastewater

In that context, this research “Study on potential filter materials for use as substrate in constructed wetland to strengthen phosphorus removal from swine wastewater” is necessary to strengthen P removal by CWs from swine wastewater

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Research objectives and scope

This study has three main objectives as follows:

(1) To determine potential filter materials for use as substrate in CWs for P removal

• To compare filter materials (based on adsorption capacity and other selection criteria)

(2) To understand the physio-chemical and adsorptive characteristics of the selected material

• To understand physicochemial properties of selected material;

• To clarify adsorption behaviors (adsorption capacity, adsorption speed, adsorption efficiency in synthetic and real wastewater) of the selected material;

• To evaluate the suitability of the selected material for use in CWs (3) To evaluate the applicability of the selected material as the substrate in CWs for

P elimination

• To evaluate the P treatment performance in CWs

• To evaluate the contribution of different components (substrates, plant) in CWs

• To evaluate the lifespan of the CWs

Research significance

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Thesis’ outline

The research’s outline is shown in the Figure This thesis contains of chapters The main content of each chapter is presented as follows:

Introduction provides the research background, identifies research objectives, research scope, main tasks, and research significance

Chapter 1: Literature review provides information about phosphorus pollution and consequences, the relevant regulations and treatment technologies The focus is placed on the role of substrate in CW for removing phosphorus from swine wastewater

Chapter 2: Research materials and methodology describes the materials, equipment, and methods used in this study Experiment setting-up is described in detail The analytical methods as well as instruments are also introduced

Chapter 3: Result and discussion provides results on phosphorus adsorption capacity, physicochemical properties of materials, isotherm, kinetics and column studies, and P treatment performance in the CW-adsorption system

Chapter 4: Conclusion and recommendation summaries the main findings, limitations of this research and further research directions

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Figure 1: Thesis‘s outline

Introduction

Chapter 1: Literature Review P pollution and its consequences

P removal technologies

P removal by substrate in CWs

Chapter 2: Materials and Methods Materials and equipment

Analytical and data statistical methods Experiment setting up

Chapter 3: Results and Discussion Screening potential filter material

Intensive investigation of selected material

P treatment performance in CW system

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CHAPTER

LITERATURE REVIEW

1.1 Phosphorus (P) pollution and its consequences

Phosphorus is a crucial nutrient that extremely needed for the growth of plant and animals (Han et al, 2015) It is an abundant element in the earth’s crust and also a vital component of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), adenosine triphosphate (ATP), phospholipids, teeth and bones in animal bodies (Nguyen et al., 2012) In addition, phosphorus also plays a key role in industrial processes, it is a major material for several principal industries (e.g fertilizers, metallurgical industry, detergents, paints, and pharmaceuticals) (Nguyen et al., 2012)

Nevertheless, the excessive loading of P in water bodies is a major cause lead to eutrophication, this process is a serious threat to water resources (Ruzhitskaya and Gogina, 2017)

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The concentration of P in the aqueous medium reaches 0.02 mg/ L can cause to eutrophication (Ismail, 2012; Nguyen et al., 2012) This phenomenon is characterized by excessive plant and algal growth The large consumption of oxygen for the dead algae decomposition, resulted in the dissolved oxygen can be reduced dramatically in aquatic medium, and thus threatening the aquatic animal living as discussed by Nguyen et al (2012) Consequently, the reducing water quality, losing biodiversity, damning economic and recreational value and posing significant public health risks (Wilson et al 2006; Tillmanns et al 2008)

Therefore, P should be eliminated from wastewater before discharged into the environment

1.2 Regulations related to P removal

The excessive amount of phosphorus in aqueous medium due to both of natural sources and human activities can cause in negative impacts on ecosystems Therefore, several guidelines and standards that have been published for protecting and controlling phosphorus pollution in natural water bodies and wastewater effluents (Gibbons, 2009)

Table 1.1 Effluent discharge standards of different countries

Country

Total phosphorus unless otherwise indicated (mg/L)

Year Source

USA, Colorado

0.7 (New plants) (Existing plants)

Colorado Regulation No31 and No85

USA,

Wisconsin

Wisconsin Dual Legislation

USA, Montana

1 (TN 10 mg/ L, Q>1 mgd)

2 (TN 15 mg/ L, Q<1 mgd)

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Canada 1976

Guidelines for Effluent Quality and Wastewater

Treatment at Federal Establishments

Australia, Tasmania

0.5 -

2001

Emission Limit Guidelines for Sewage Treatment Plants that Discharge Pollutants in Fresh and Marine Waters June 2001 Northern

Ireland 0.7-1.5

1972 Environment and Heritage Service (EHS) European

Union

1 (> 100,000 PE)

2 (10,000 -100,00 PE) 1991

European Union Urban Waste Water Directive

Japan 16 1993 Japan National Effluent

Standards

China 0.5 (Level A) (Level B)

2006 China National Standards

India (dissolved P) 1986

General Standards for Discharge of Environmental

Pollutants

Vietnam (Category A)

6 (Category B) 2011

QCVN 40:2011/BTNMT (Industrial Wastewater

Discharge Standards) Source: Nguyen et al., 2013

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the maximum concentration of P discharge into aqueous medium is 0.1 mg/ L (Ramasahayam, 2014)

In order to minimize the pollution burden on surface water as well as to control phosphorus pollution at the source Some countries have developed and applied national regulation of effluent discharge standards as shown in the Table 1.1

It can be seen that the effluent discharge standards vary from one region to others in a country (USA) as well as one country to another This can be explained by the variation in the level of treatment technologies and background phosphorus concentrations in the water bodies in different regions and countries (Nguyen et al., 2013) To prevent P pollution from the consequences of rapid economic development, China also has developed strictly for phosphorus regulations with the low-acceptable P concentrations (0.5-1 mg/ L) (Wang et al., 2013)

In Vietnam, P regulation is applied in some types of water such as Industrial wastewater Discharge Standards (4-6 mg/ L), the effluent of aquatic Products Processing industry (10-20 mg/ L), Health Care wastewater (6-10 mg/ L), domestic wastewater (6-10 mg/ L) Nevertheless, most of the effluent discharge standards are higher than developed countries and much higher than EPA criterion

Although, each country has the effluent discharge standards is different, however, the most stringent regulations have suggested that the total concentration of P in the effluent only should be kept from 0.5 to mg/ L before being discharged into the water environment (Xu et al., 2011a)

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1.3 Phosphorus treatment technologies

There are many technologies for phosphorus removal as shown in Figure 1.2 (Nguyen, 2015) Each method has distinctive characteristics and presents its own merits and demerits

Figure 1.2 P treatment technologies (Nguyen, 2015)

1.3.1 Physical methods

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Membrane technologies

Membrane technology is playing a key role in improving the quality of wastewater treatment, in particular for P elimination

Besides the phosphorus removal in the TSS, dissolved phosphorus also can be removed by membranes According to Reardon (2006), the P concentration of several plants have been reported that they have been achieved less of 0.1 mg/ L in the effluent

Magnetic separation

In 1970s, magnetic separation method was beginning investigated for phosphorus treatment This is considered as an attractive method because at the same cost with other methods, the phosphorus level in effluent can be reached to 0.1-0.5 mg/ L by magnetic separation

Magnetic separation may be applied as a reliable add-on technology for chemical removal Phosphates in solution are combined with reagent into insoluble compounds And after that, magnetic material is used to isolates phosphate-containing sediment The significant benefits of this process are simple process, and low energy consumption However, it has low elimination efficiency (<10 %) in case of microfiltration and in term of high cost for RO and electrodialysis (Biswas, 2008)

Ion exchange

Ion exchange is a process relied on chemical interactions between ions in liquid phase and ions in solid phase (Martin et al., 2009)

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1.3.2 Chemical methods

Chemical method has been widely utilized for elimination of phosphorus, in response to increasing concern over eutrophication (Ruzhitskaya and Gogina, 2017)

Precipitation

This method is applied by using chemical to form phosphate precipitates, which are subsequently separated by sedimentation (Nguyen et al, 2012)

These chemicals combine with phosphate as shown by the following reactions Al3+ + PO43- → AlPO4↓

Fe3+ + PO43- → FePO4↓

5Ca2+ + PO43- + OH- → Ca5(PO4)3(OH)↓

The most common chemicals employed for this method are iron (II, III) and aluminium (Thistleton et al., 2001)

This treatment performance is influenced by some parameters such as pH, TSS, dissolved organics, type of the precipitant, location of dose application, and mixing conditions The treatment performance of chemical method is high According to Nieminen, (2010), there are more 90 % of the total P might be eliminatedd by this method Nevertheless, this method still has several drawbacks, such as high chemical cost, potential sludge formation, insufficient efficiency for phosphorus with low concentration (Biswas, 2008; Mallampati and Valiyaveetttil, 2013) The sludge handling will increase the treatment cost and require much space (Lanning, 2008) In addition, the end-products of chemical methods are non-reusable, due to high impurities and low bioavailability (Nieminen, 2010) Besides, it is hard to identify the optimal dosing conditions (Biswas, 2008)

Crystallization

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This process occurs on filters or in the suspended sludge, which include magnesium ammonium phosphate (MAP) and hydroxyapatite processes

However, crystallization phosphorus removal method is not widely applied because of very high cost (Biswas, 2008)

Adsorption

Among various phosphorus removal technologies, only adsorption method holds the potential for phosphorus recovery (Nguyen et al., 2012; Zhang et al., 2014) P from wastewater is attracted by intermolecular forces onto surface of solid adsorbent and keeps in there This method is widely used for both high and low level of phosphorus in various wastewater (Nguyen et al, 2012)

According to Biswas (2008), the feasibility of the phosphorus adsorption process mostly relied on the preparation of adsorbents Formerly, activated carbon was commonly applied to remove phosphorus However, its application is not wide, in particular in developing countries because the problems relate to high expense and no renew ability (Karthikeyan et al., 2004) Therefore, using abundant availability, low-cost materials (eg industrials products, agricultural by-products) with high efficiency, potential renewability and adaptation are trending new approach (Biswas, 2008, Ning et al., 2008)

1.3.3 Biological methods

Biological method for phosphorus removal was developed in the late 1950s, and it has shown to be a firm technology This method ensures the best removal of phosphorus, as they help to maximize the biological potential of activated sludge (Ruzhitskay and Gogina, 2017)

Enhanced biological phosphorus removal (EBPR)

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Figure 1.3 Metabolic pathways of PAO (Bunce et al., 2018)

EBPR is also a green approach to the elimination of phosphorus However, the phosphorus treatment performance is limited (≤30 %) Additionally, microorganisms are less adapted with the variation of environment Moreover, this method could not treat effectively with trace levels of phosphorus (Bunce et al., 2018)

Constructed wetlands

Constructed wetlands (CWs) are engineered systems for decontaminating wastewater based on natural functions of filter media, plant and organisms (Vymazal, 2007)

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Ca2+, Al3+, Mg2+, Fe3+, and Mn2+ ion in substrates is an important way to remove P

in constructed wetland system (Vymazal, 2007)

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Table 1.2 Phosphorus removal efficiencies of different methods

Method Works

application

P initial concentration

(mg/L)

P removal efficiency (%) -

adsorption capacity (mg/g)

Types of wastewater Reference

Membrane Secondary or tertiary treatment

0.05-0.222 90 % River water Dietze et al., 2003

6-13 > 90 % Real wastewater Gnirss et al., 2003 94.1 % Domestic wastewater Smith et al., 2014 Magnetic

separation

Tertiary treatment only

0.5 98 % Synthetic wastewater Zhao et al., 2012

0.2 > 90 % Synthetic wastewater Merino et al., 2011

Ion exchange Tertiary treatment only

500 50 mg/ g Synthetic wastewater Martin et al., 2009 50 51.52 mg/ g Synthetic wastewater Ren et al., 2014

90 % Synthetic wastewater Seo et al., 2013

Precipitation Primary, secondary or tertiary treatment or activated sludge recycle

5 92 % Synthetic wastewater Ramasahayam et al.,

2014

50 70 % Piggery wastewater My et al., 2017

Crystallization Tertiary treatment or recycle stream

1 91 % Synthetic wastewater Joko, 1985

25 91.30 % Synthetic wastewater Xuechu et al., 2009 30-120 96.10 % Synthetic wastewater Menglin et al., 2016

5 91 % - (120 mg/

g) Synthetic wastewater

18 Adsorption Secondary or

tertiary treatment

100 > 90 % - (4.75

mg/ g) Synthetic wastewater Nguyen et al., 2013 30 98.20 % Synthetic wastewater Vohla et al., 2010 - 25 95% (3.11 mg/ g) Synthetic wastewater Vohla et al., 2010

EBPR

Secondary or tertiary treatment

or activated sludge recycle

16.67 99 % Synthetic wastewater Ong et al., 2016

Constructed wetlands

Secondary or tertiary treatment

or activated sludge recycle

10 25 % dairy wastewater Hill et al., 2000

5 96 % leachate wastewater Vohla et al., 2005

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1.4 Constructed wetlands (CWs) system for wastewater decontamination 1.4.1 Definition

Constructed wetlands (CWs) are engineered systems that have been designed and constructed to strengthen the natural processes for wastewater treatment (Vymazal, 2011) These systems comprised of major components such vegetation, substrates, soils, microorganisms and water The various contaminants from wastewater are removed by natural microbial, biological, physical and chemical process in CWs (Vymazal, 2011; Saeed and Sun, 2012)

1.4.2 Classification

There are various types of CWs that can be distinguished based on the dominant vegetation type, hydrology and flow direction (Zheng et al., 2014)

Nevertheless, according to the majority of authors, most of CWs are typically classified into the two types: free water surface flow and subsurface flow (Almuktar et al, 2018)

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Free surface water flow:

Figure 1.5 The schematic surface flow constructed wetland (Almuktar et al., 2018) Free water surface flow (FWS) systems are designed similar to natural wetlands, they include an aquatic area with a variety of plants, a sealed basin filled with 20-30 cm of substrates and about 40 cm for the depth of water (Stefanakis et al., 2014) These systems are also considered as expected habitats for many wildlife species

In free surface flow systems, organic compounds in wastewater are effectively removed through primarily the process of sedimentation, filtration and decomposition of microorganisms Nitrogen is effectively treated by denitrification and ammonia volatilization However, phosphorus is unable to effectively removed because the water does not tend to come in contact with soils particles (which adsorb and precipitate with P) as discussed by Taylor et al., 2006

Thus, if phosphorus is the key contaminant of concern, the FWS systems are less suitable for treatment Additionally, the high possibility of human exposure to pathogens and the large area requirement are also disadvantages of these systems

Subsurface water flow (SSF)

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According to the flow direction, SSF might be classified into two types: vertical flow (VF) and horizontal flow (HF) (Almuktar et al., 2018) In HF constructed wetlands, the substrates are flooded by water, while VF constructed wetlands are applied intermittently to gain the high rate of oxygen transfer (Stefanakis et al., 2014)

Figure 1.6 The schematic vertical flow constructed wetland (Almuktar et al., 2018)

Figure 1.7 The schematic horizontal flow constructed wetland (Almuktar et al., 2018)

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surface flow constructed wetlands Because they can be controlled by selecting highly P adsorbablesubstrates as discussed by Pant, 2001 and White 2011

In addition, the role of root-bed media for phosphorus sorption also is very important They facilitate better to remove P from aqueous media for longer time (Pant et al., 2001; Seo et al., 2005) White et al (2011) reported that the P removal of root-bed substrates could be reached around 74 % by using substrates such limestone, oyster shells, crushed brick The viability of the substrate for P removal depends on its maximum adsorption capacity The saturated substrates must be removed and processed, then the new substrates need to be added periodically to maintain P adsorption capacity This is a drawback of SSF constructed wetlands

Hence, the monitoring and evaluating the life of substrates are extremely important and necessary to maintain the P-sorption capacity and to minimize the P export from the saturated (White et al., 2011)

Hybrid systems

Hybrid systems were developed to overcome the limitations of single stage CWs, because many wastewaters could be difficult to treat in individual systems (Vymazal 2005, 2007)

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high (Vymazal 2011) Thus, hybrid systems have the combination of HF and VF can be obtained higher nitrogen removal efficiency (Zhang et al., 2014)

In recent years, the hybrid systems are used widely for many type of wastewater According to Serrano et al., 2011 this combined system was used effectively for winery wastewater, and wastewater in oil field (Alley et al., 2013), industrial wastewater and grey water (Vymazal 2014; Comino et al., 2013), swine wastewater (Kato et al., 2013; Zhang et al., 2016), pharmaceuticals (Reyes et al., 2011)

In generally, constructed wetland is a potential technology, and the attractive alternatives to traditional wastewater treatment methods The improvements to enhance treatment efficiency for many wastewater types in CW are still being concerned and developed (Zhang et al., 2014)

1.4.3 Application of CWs in wastewater treatment

In the world

CWs have been used for quite a long time The first experiment was implemented by Käthe Seidel at Germany in 1950s with the attempt aimed using CWs to treat wastewater And lots of experiments were conducted and successfully applied in later At the initial stage, most the application of CWs were utilized to treat conventional municipal and domestic wastewater (Wu et al., 2015)

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effluents (Stefanakis, 2018) Additionally, they have been widely developed in various climate conditions (e.g cold, tropical, warm etc) (Vymazal, 2015)

To improve the treatment performance of CWs, there are lots of studies investigated the factors that effect to its treatment efficiencies Many studies examined the effect of hydraulic loading rate (HLR) and hydraulic retention time (HRT) Ramprasad et al (2017) found that elimination of phosphorus efficiency was more at higher HRT In regard of biomass harvest and management, many international studies showed the positive impacts of multiple biomass harvest on the phosphorus removal Specifically, Březinová and Vymazal (2015) observed that the amount of phosphorus removed through multiple biomass harvesting may increase up to 43 % compared to a single harvest Concerning the seasonal variation, Ramprasad et al (2017) released that phosphorus removal rate in the summer was higher than that in other seasons Relating to evapotranspiration, Bakhshoodeh et al (2017) reported that when evapotranspiration started to rise, phosphorus removal efficiency decreased Since the filter media is the main component of the CWs, it was of great interests of many international researchers Barca et al (2014) found that, using steel slag as filter material can removed over 88 % total phosphorus in influent Andreo-Martínez (2017) obtained extremely high removal efficiency of phosphorus (96.9±1.7 %) by applying blast furnace slags as filter media in the HF-CWs for reclaiming domestic wastewater

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In Vietnam

In Vietnam, the CW model is still quite novel and not widely applied So far, CWs have been applied for the purification of several kinds of wastewater, for instance sewage conveying river water (Nguyen et al., 2011), domestics wastewater (Ngo & Han, 2012; Nguyen, 2015; Nguyen, 2016); landfill leachate (Nguyen, 2012), However, to the knowledge of the author, very few studies on swine wastewater treatment using CWs can be found (Le, 2012; Ngo, 2013; Nguyen, 2016; Vu et al., 2014)

It is recognized that the performance of CWs is affected by many factors Several studies examined the effect of hydraulic loading rate (HLR) and hydraulic retention time (HRT) (Ngo and Hans, 2012; Ngo, 2013; Vu et al., 2014), a few studies implemented to show the role of filter materials in the CWs (Ngo and Hans, 2012; Nguyen, 2008; Nguyen, 2015) So far, there has been no studies in Vietnam on mass balance study to interpret phosphorus removal mechanisms The information on role of microorganisms in the CWs is also lacking In contrast, these are the focus of international studies

1.4.4 Factors influencing the CWs treatment performance

a. HRT (Hydraulic retention time)

26

In addition, Avila et al (2014) investigated the possibility of removing emerging organic contaminants by using hybrid CW systems, this result pointed out that the elimination of phosphorus reduced as the HRT decreased

b. HLR (Hydraulic loading rate)

Hydraulic loading rate (HLR) is the amount of loading water per unit area It is an important factor in monitoring and operating CWs (Wu et al., 2015) A greater HLR boosts quicker the movement of wastewater through the media, results in the contact time of wastewater and media reduced An adequate microbial community unable to establish with short contact time (Wu et al., 2015)

Cui et al (2010) reported that the ammonium and TN treatment efficiency was reduced from 65 % to 60 % and 30 % to 20 % respectively in domestic wastewater with increasing HLR from to 21 cm/ d However, Stefanakis and Tsihrintzis (2012) showed that the nitrogen and organics removal efficiencies in synthetic wastewater by VF CWs were increased as HLR increased

Thus, depend on the types of CW and wastewater that need to have appropriate HLR Therefore, to ensure the treatment performance in CWs, the optimal design of HLR is extremely necessary

c. Feeding mode of influent

The feeding mode is also a key design parameter (Vymazal, 2011) The treatment performance in CW also relies on the different feeding mode of influent

27

However, Saeed and Sun, (2012) indicated that the nitrogen and organic compounds removal efficiencies could be enhanced with intermittent feeding mode Additionally, Caselles-Osorio and García (2007) investigated the contaminants treatment efficiency in SSF CWs by the continuous and intermittent feeding modes, and noted that continuous s feeding modes is lower than to intermittent feeding mode for ammonium removal efficiencies Jia et al (2010) also reported that the COD and TP removal efficiencies in VF CWs by intermittent feeding modes are slower than continuous feeding modes

Generally, the feeding modes influence to the treatment efficiency of CW Thus, depending on the primary contaminant of concern, has suitable selection for feeding mode

d. Types of CWs

Type of CW also has been shown to be a factor that effect to treatment performance of CW

FWS CWs can remove effectively to organics and suspended solids via microbial degradation, filtration and sedimentation (Zhang et al., 2014) However, this system could not remove effectively to phosphorus, due to the limitation contact of water and substrates as discussed by Vymazal, (2011)

Compare to FWS CWs, phosphorus can be treated greater in SSF CWs because the wastewater tend to comes into contact with filter media (Zhang et al., 2014) VSSF CWs can remove nitrogen more effective than HSSF CWsVymazal (2007)

28

Generally, beside other factors, the type of CW also influences to the treatment performance of CW Thus, to select an appropriate type of CW, it is necessary to determine the primary of the concern

e. Substrates (medium)

The substrate is a key component of the CWs, it is very important in SSF CW, because it can provide an appropriate growing media for plants as well as keep various pollutants (Nguyen, 2015) Furthermore, filter materials adsorption plays extremely an important role in the removal of numerous contaminants such as phosphorus (Ju et al., 2014) Therefore, selection of appropriate substrate using in CW is important

Many studies were carried out to select potential substrate could be alternative conventional materials in CWs by using the artificial and industrial products Barca et al (2014) reported that over 88 % of total phosphorus was removed by using steel slag as filter material, Nguyen, 2015 also used coal slag to enhance P removal from domestic wastewater

f. Plant

Plant is another important component and could play a strategic role in CWs Many international studies focused on plant selection by evaluating and comparing their treatment efficiencies (Zhang et al., 2014)

Ong et al (2010) revealed that the total phosphorus elimination efficacy in CWs planted with Manchurian wild rice (52 %) was considerably higher than that in CWs planted with Phragmites australis (34 %) Adhikari et al (2015) reported the P removal rate of duckweed in the surface flow CWs was 7.4 g N/ m2/ yr

29

Moreover, the biomass of plant is important for removing of pollutants Specifically, Březinová and Vymazal (2015) observed that phosphorus removal efficiency via multiple biomass harvesting might be increased up to 43 % compared to a single harvest This is the same with the finding of Hernández-Crespo et al (2016) that a multiple harvest of Iris pseudacorus increased the nutrients removal efficiency up to 50% for N and 100 % for P compared with a single harvest Similarly, Luo et al (2017) discovered that multiple harvest of

Myriophyllum aquaticum from SFCWs contributed up to 22.5-59.6 % of total removed phosphorus mass

1.4.5 Mechanisms of P removal in CWs

Figure 1.9 Phosphorus cycle in constructed wetland (Reddy et al., 1999)

Mechanism of phosphorus removal in CWs includes plant uptake, accumulation of microorganisms, absorption and precipitation of substrates… (Vymazal, 2007)

30

soluble organic phosphorus to dissolved inorganic phosphorus which plants can easily to absorp Phosphorus is also removed by adsorption and precipitation of substrates The combination of phosphorus with Ca2+, Al3+, Mg2+, Fe3+, and Mn2+ ion in substrates is an important way to remove P in constructed wetland system However, it will be limited when the substrate has low adsorption or reach to saturation

In generally, long-term removal of phosphorus from a given ecosystem can only occur when vegetation is harvested or when sediment bound phosphorus is removed from the system (Vymazal, 2007)

Table 1.3 Mechanism of phosphorus removal in constructed wetland system

Mechanism Description

Sedimentation Particulate phosphorus settles out of the water column

Adsorption Chemical bonding of phosphorus to iron, aluminum, and calcium on soil particle exchange sites

Precipitation Phosphorus binds to dissolved iron, aluminum, and calcium to form a solid or semi-solid

Uptake by Vegetation Orthophosphates and some organic phosphorus taken up by plants and algae

Immobilization

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1.5 Removing P by substrates in CWs

1.5.1 The role and mechanism of P removal by substrates

Substrate plays an important role for phosphorus removal The contaminants can be removed from wastewater through exchange, adsorption, precipitation and complexation process (Wu et al., 2015)

Depend on the physicochemical properties of filter materials that the mechanism will be dominant The phosphorus removal capacities are depended on the contents of calcium, iron, aluminum and their oxides and hydroxides (Yang et al., 2018) such as phosphorus was removed effectively by the use of steel slag (44.3 % of CaO , 16.9 % of Al2O3 and 24.2 % of Fe2O3) (Park et al., 2016), limestone and scallop shells (mainly

CaCO3) (Nguyen et al., 2014), BOF-slag (47.08 of CaO, 36.12 % of Fe2O3 8.04 % of

SiO2 , 4.94 % of MgO) (Han et al., 2015)

1.5.2 Selection criteria

The selection of substrate with high efficiency, abundant availability, durability, appropriate cost, less side effects has been a crucial issue in constructed wetlands

The P adsorption capacity of filter materials depends on its physicochemical properties The chemical composition of materials plays a crucial role for P removal because the phosphorus is mainly removed via adsorption and precipitation process, it means that the Ca, Al, Fe contents is important for the effective P removal However, the chemical composition may also be to side effects when they can affect to the electrical conductivity, pH, and heavy metal release Hence, the filter media should be selected very careful (Vohla et al., 2011)

Besides, the hydraulic conductivity is also considered an important issue for selection of substrate To avoid clogging, the material must have durability, porosity and reasonable size (Vohla et al., 2011)

32

cost of CWs system, substrate should use locally abundant, available material and no or low cost

In recently, toward to the using of reuse waste as substrate for P removal in CWs is also gaining the special interest Using of reuse waste in CW, not only improving contaminants treatment and reducing the large volume of solid waste in a environmental friendly way but also providing additional economic value to the waste (Yang et al., 2018)

1.5.3 Classification

The filter materials used in CWs for P removal can be classified based on their use history, origin or pollutant removal mechanism

For origin of materials, they could be classified into three groups including natural materials, industrial by-products and manufactured products (Cucarelle and Renman, 2009)

Table 1.4 Some filter media used for P removal

Material Study type

P retention – initial concentration

(mgP/L)

References

Natural materials

Apatite Batch 4.5mg/g - (500mg/L) Molle et al., 2005 Dolomite Batch 7.34mg/g - (60mg/L) Karaca et al., 2004

Gravel Full-scale CW 25.8mg/g - (100mg/L) Tanner et al., 1999 Limestone Batch 0.3mg/g - (25mg/L) Johansson, 1999a

Opoka Batch 0.1mg/g - (25mg/L) Johansson, 1999a

Oyster shell (burnt) Batch, column 0.83mg/g - (320mg/0L) Seo et al., 2005 Sand Full-scale CW 0.165mg/g - (10mg/L) Vohla et al., 2007

Shellsand Batch 4mg/g - (1000mg/L) Roseth, 2000

Industrial by-product

33

Ochre Batch 2.6mg/g - (1500mg/L) Heal et al., 2003 Sediment of oil

shale ash Batch 8.2mg/g - (333mg/L) Vohla et al., 2005 BOF slag column 9.15mg/g - (320mg/L) Kim et al., 2006 Electric arc furnace

(melter) slag Full-scale CW 2.2mg/g - (400mg/L) Shilton et al., 2005

Artificial products

Filtra P Column 3.8mg/g Gustafsson et al.,

2008 Leca (Estonian) Full-scale CW 10mg/g - (333mg/L) Ưưvel et al., 2007

Norlite Full scale P removal: 34% Hill et al., 2000

In general, there are various materials that have been studied and used to enhance P removal In addition to natural materials, nowadays the trend of using artificial materials and industrial by-products has been gaining more attention, this waste is also treated by an environmentally friendly way

1.6 Overview of research objects 1.6.1 Swine wastewater

The characteristics of swine wastewater depends on various factors such as the age and diet of pigs, temperature, humidity of a building, housing or confinement methods, waste removal procedures, and pre-processing (Lime, 2008)

According to Saucedo et al (2017), a medium-sized pig farm can generate to 35 m3/ day of swine wastewater, which consist of high levels of organic matters,

34

In Vietnam, it is estimated that livestock farms national wide produce 64.33 million tons of manure and 54.44 million tons of urine each year Of which, pig farms account for 41.24 % and 53.82 %, correspondingly The livestock waste is mainly treated using biogas However, wastewater after biogas treatment usually not meet the Vietnam environmental standards of discharge for cattle and poultry farm, according to QCVN 01 - 79: 2011/BNNPTNT Thus, it poses a big threat to the environment in rural areas of Vietnam and requires further treatment before discharging into the environment (Tong Xuan Chinh, 2017)

Table 1.5 The main composition of swine wastewater after anaerobic digestion by biogas chamber

STT Parameter Unit Concentration QCVN

40:2011/BTNMT

1 BOD5 mg/L 192-582 50

2 COD mg/L 264-789 150

3 VS mg/L 188-821 100

4 VSS mg/L 123-499 -

5 N-NH4+ mg/L 106-421 10

6 TKN mg/L 335-712 -

7 TP mg/L 122-492 6

35

loading rates, less energy consumption (Ngo & Hans, 2012; Ngo, 2013; Nguyen, 2016) Besides, it can also contribute to enhancing the biodiversity, renovating environmental landscape, ecology of local areas (Greenway, 2005; Nguyen, 2015; Wu et al., 2015a)

All of which above mentioned, CW has been shown to be a promising technology for swine wastewater treatment

1.6.2 Ca-rich bivalve shell as the substrate in CWs

a. Bivales and bivales shells concern to environment

Bivalves are rich nutrient food from coastal and riverside source They include clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater and in freshwater

In the world

Shellfish cultivation is developing strongly and contributing significantly to economic activity in the world (Yao et al., 2014) It is account for 40 % of total marine aquaculture production (FAO, 2011) According to Yao et al (2014), in China, the shellfish production has over 10 million tons, in which the majority of shellfish production are clam, scallop, oyster and mussel They represented more than 83.8% all of shellfish species

The strong development of shellfish production has generated a large of volume shell waste Kusterko, S K (2006) reported that for kg oysters consumed would produce 370-700 g of shells

36

discharged as a waste and must pay for the treatment of this waste And all of them are also dumped into landfills (Yeom and Jung, 2009)

The large of shell waste negatively affects to the environment Mostly the waste is dumped arbitrarily into fields, reclaimed lands or into public waters These are difficult to decompose in the natural environment, without treatment they can cause to poisonous odors such hydrogen sulfide, ammonia and amines gas as a results of decomposition remaining meat (Yao et al., 2014)

In case of Vietnam

With the advantage of long coastline (3.260 km) and interlaced network of rivers and streams Vietnam has high potential for coastal aquaculture The aquaculture sector has contributed considerably to social security and national economy (Ngo, 2015), in which has to mention to clam farming

Coastal clam farming has been growing successfully in Vietnam for years Clam species are cultured for domestic and export markets including White hard clam (Meretrix lyrata) Currently, clam has strongly grown for farming area, production as well as the intensive farming level According to the report of the Department of Aquaculture (2011), the total area of clam culture in whole country in 2010 was more than 15,000 ha, reaching an output of over 85,000 tons, of which export was 19,000 tons with export value of about 40 million USD The Ministry of Agriculture and Rural Development reported that it is also predicted to 2020, the area of clam farming will be increased to 32,960ha and the productivity is expected to reach to 430,700 tons

37 White hard clam

(Meretrix lyrata)

Oil clam (Meretrix meretrix)

Razor clam (Paphia undulate) Figure 1.10 The main clam species in Vietnam

Besides the processing of clam meat, waste clams shell after processing is also a concern of the producers (Ngo et al., 2017) In recently, most companies must pay for burying of this waste According to the report of Thai Binh shellfish Co., Ltd, it is estimated that each year, the company has to pay up to billions VND to bury clam shells However, due to the large volume of clam shells, the insufficient treatment still causes to environmental pollution such as bad smell, growth of pathogen, water pollution

b. Bivalve shell is used as adsorbents

The composition of bivalve shell contain mainly of CaCO3 This is a potential for use raw material as well as adsorbents (Yao et al., 2014)

Table 1.6 The main chemical compositions of bivalve shells and limestone

Oxides (%) Oyster Mussel Clam Short necked

clam Limestone

CaO 51 54 54 53.6 54.7

Al2O3 0.5 0.13 0.2 0.4 0.07

SiO2 0.2 0.46 0.46 1.62

MgO 0.5 0.33 0.22 0.2 0.25

Fe2O3 0.2 0.03 0.04 0.04 0.12

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Bivalve shell has been used for soil conditioner (Asaoka et al., 2009; Alvarez et al., 2012), catalysts (Hu et al., 2011), construction material (Yang et al., 2005; Yoon et al., 2003), calcium supplements (Finkelstein et al., 1993; Guinotte and Nys, 1991; Ngo et al., 2015;), Fillers (Jackson et al., 1988; Li et al., 2012)

It can be seen from the Table 1.6, the amount of CaO in the bivalve shells close to that of limestone, as a result it a potential to use adsorbent for removing phosphorus Moreover, to enhance P removal, the bivalve shell is modified from natural bivalve shell The common modification method is using high temperature By the pretreatment methods (calcination, pyrolysis, hydration), the amount of calcium carbonate could be converted into calcium oxide and calcium hydroxide that easily react with phosphates anion (Yao et al., 2014)

39

Table 1.7 Some studies used bivalve shell for P removal

Materials Modification

condition

P initial concentration

(mg/L)

P adsorption capacity

(mg/g)

R removal efficiency

(%)

Type of

wastewater Size (mm) Study type Reference

Cockle shell

750oC, 1h 0.85 – 2.21 87.63 Shrimp farm

effluent 0.85-2.0 Lab-scale

Aopreeya et al., 2013

No 0.85 – 2.21 43 Shrimp farm

effluent Lab-scale

Aopreeya et al., 2013

No 0.5-5 1.04 88 Synthetic

wastewater powder Lab-scale Kim et al., 2018

Mussel shell

No 0.5 1.8 60 Synthetic

wastewater < Lab-scale

Paradelo et al., 2016

550 oC, 15min 0.5 2.2 77 Synthetic

wastewater < Lab-scale

Paradelo et al., 2016

700 oC, 20min 20 6.15 55 Synthetic

wastewater powder Lab-scale

40

Oyster shell

800 oC, 1h, N

2 30 98

Synthetic

wastewater Kwon et al., 2004

No 16.8 95.5 Domestic

wastewater 0.3-6 Pilot scale

Park and Polprasert, 2008

Scallop shell

NaOH 1.5M, HCl 1.5M, NH4CO31M,

120 oC, 24h

100 9.92 99.2 Synthetic

wastewater 0.045 Lab-scale

Yeom and Jung, 2009

NaOH 1.5M, HCl 1.5M, NH4CO3 1M,

120 oC, 24h

500 21.8 43.6 Synthetic

wastewater 0.045 Lab-scale

Yeom and Jung, 2019

600 oC, 45min 13.6 Synthetic

wastewater 2-3 Lab-scale Chen et al., 2014)

Clam shell

No 20 0.85 97.6 Synthetic

wastewater Lab-scale Xiong et al., 2015

700 oC, 20min 20 98.7 Synthetic

41

CHAPTER

MATERIALS AND RESEARCH METHODOLOGY

2.1 Materials and equipment 2.1.1 Materials

Filter materials:

Seven kinds of filter materials have been investigated in this study, including Limestone (LS), Laterite (LA), Coral (CR), Coal slag (CS), Steel slag (SS), White hard clam (WHC) and Okara (OK) These materials were obtained from different locations inVietnam, such as Chuong My, Ha Noi (LS, LA), Buoi market, Cau Giay, Hanoi (CR), Hai Duong thermo power plant (CS), Thai Nguyen steel corporation (SS), Tien Hai, Thai Binh (WHC) and tofu production household (OK) First, all materials were washed with tap water to remove contaminants on the surface, which may affect on adsorption experiments Next, the washed materials were dried in the oven (Thermo Fisher Scientific REL404A20,) at 8000C for h to a constant weight After that, the washed, dried materials were sieved to get the desired particle size of 1.4-2.0 mm

Limestone Laterite Coral

White hard clam Coal slag Steel slag Okara

42

WHC: WHC was collected from Thai Binh shellfish Co., Ltd, Nam Thinh commune, Tien Hai district, Thai Binh province (20°23'34.1"N 106°34'28.3"E) It is one of the largest frozen clam processing and exporting factories in the north of Vietnam, with a capacity of over 20 ton/day In recently, the company has exported successfully clams to the European, Japan, Taiwan, South Korea markest It has greatly contributed to the Vietnam's seafood industry After being collected, WHC was washed thoroughly with tap water, and dried in the open air till dry After that it was transported to Chuong My, Hanoi for grinding and sieving to get diferent particle sizes

43

Collecting Washing Drying

Packing Crushing Storing

Figure 2.3 Procedure to prepare WHC as phosphorous adsorbent

Synthetic and real swine wastewaters:

The real swine wastewater was collected from a pig farm in Chuong My, Hanoi, Vietnam (Coordinates: 20°53'49.6"N 105°42'57.9"E) This farm has a total area of around 1,700 m2 with 1,100 pig heads It is estimated that approximately 55 m3/d was generated and discharged into the surrounding environment after biogas

treatment The wastewater was transported to the laboratory right after collection, filtered through 0.45 µm mesh filter paper, and kept in the refrigerator at 0C The pH, turbidity, and DO were measured on site, whereas other parameters, such as COD, BOD, TN, N-NH4, TP, P-PO43- were analyzed at the laboratory of Master’s

44

Figure 2.4 The pig farm in Chuong My, Hanoi

The synthetic swine wastewater was prepared to simulate real swine wastewater For batch and column adsorption tests, synthetic swine wastewater contained only phosphorus In contrast, the synthetic used for constructed wetland comprised both phosphorous and nitrogen The stock phosphorus solution (1000 mg P/ L) was prepared by dissolving KH2PO4 into distilled water Depending on the

purposes of different experiments, the working solutions were prepared from stock solution with the appropriate dilution factors For constructed wetland experiment, the synthetic swine wastewater was prepared by dissolving KH2PO4 and NH4Cl in

tap water to get the concentration of 12.5 mg P/ L and 125 mg N-NH4/ L

Plant: In this work, Upon paspalum was selected to plant in CWs at the age of 1.5 months, with a height of 25 cm The seedings of the plant was purchased from Buoi market, Caugiay, Hanoi, and grown in a garden in Tien Hai, Thai Binh After planting 1.5 months, the plants were harvested, washed with tap water to remove soil, kept in a bucket of water for days and then a nutrient solution (12.5 mg P/L and 125 mg N/L) for adaptation before being transferred into CWs

2.1.2 Chemicals

All reagents, which were utilized in this study, were purchased from ESQ Co., Ltd (Ba Dinh, Hanoi) These chemicals all have AR grade The solutions with different phosphorus concentrations were obtained by dissolving specific amounts of KH2PO4 into distilled water The distilled water was produced in the MEE

45

2.1.3 Equipment

AAS Agilent 280FS Model 1830

SEM/EDX NOVA 3000, N32-11 FT/IR 6300typeA

Orbital shaker (OS-3000, Jeiotech)

UV/Vis Diode Array Spectrophotome

(S2100, Unico)

pH meter (S220-Kit, Mettler Toledo)

Turbidity meter (HI98703, Hanna)

Figure 2.5 Equipments used in this study

2.2 Experiment setting up 2.2.1 Modification of materials

46

Figure 2.6 Modificatin of investigated filter materials

Modification of selected filter material (WHC): In order to identify optimum temperature for modification, thermal treatment was carried out with kg WHC at different temperatures (750, 800, and 850 0C) for the same period of time (3 h)

Then modification tests were conducted with kg WHC at the same temperature (800 0C) for various periods of time (1, 2, h) to select the most efficient contact

time The optimum modification condition was determined based on (1) phosphorus adsorption capacity of modified WHC, (2) weight loss of WHC after calcination and during adsorption tests The weight loss was calculated using the equation (2.1) as follows:

Loss weight =(m1−m2)

m1 100% (2.1)

where:

m1, the weight of WHC before calcination or adsorption (g)

m2, the weight of WHC after calcination or adsorption (g) 2.2.2 Characterization of materials

a Physical properties

47

Q = K∗A∗∆h

L (2.2)

where Q, the rate of flow (m3/s)

K, permeability of the material (m/s) h, difference in total heads (m) L, length of the soil mass (m)

A, the cross-sectional area of the soil mass (m2)

Figure 2.7 The experiment setting according to Darcy law (NPTEL, 2003) Porosity of filter materials: The purpose of this test is to determine the ability of holding water of materials, which is known as pore space (porosity) The experiment setting up was demonstrated in Figure 2.8 The porosity was calculated by equation (2.3) as follow:

Porosity =Pore space volume

Total volume ∗ 100 (2.3)

1 Measure the volume of your

sample

2 Measure a volume of water

3 Saturate the sample with water

4 Record the volume of water

48

Brunauer Emmett Teller (BET) surface area and pore size determination were implemented with Quantachrome NOVA 3000 series (Model N32-11) High Speed Gas Sorption Analyzer

Scanning electronic microscopy (SEM) analysis was carried out with Avomeen’s SEMTech Model 1830 SEM/EDS at the laboratory of Institue of Chemistry, Vietnam Academy of Science and Technology (VAST) to identify the variation in morphology of WHC as the result of thermal modification

b Chemical properties

Fourier transform infrared spectroscopy (FTIR) analysis was performed with FT/IR 6300typeA at the laboratory of Faculty of Chemistry, VNU University of Science (HUS), in order to identify the key functional groups reponsbile for adsorption reactions The spectral resolution of the FTIR is cm-1 determined

between 4000 and 400 cm-1

Energy dispersive spectroscopy (EDX) measurement was utilized on Avomeen’s SEMTech Model 1830 SEM/EDX at the laboratory of Institue of Chemistry, Vietnam Academy of Science and Technology (VAST) to deterimine change n chemical elemental composition of WHC before and after thermal treatment

c Side effects

pH: First, adsorption test was conducted at seven filter materials at the following conditions: initial phosphorous concentration of 200 mg P/L; adsorbent dose of g/ 125 mL; shaking speed of 120 rpm, shaking time of 24 h, temperature of 27 0C Then, the post-adsorption solution was measured to determine pH value

with pH meter (Mettler Toledo Seven Compact S220K)

49

2.2.3 Adsorption experiments

a Adsorption batch experiments

A stock phosphorus solution (1000 mg P/ L) was prepared by dissolving KH2PO4 in distilled water The desired working solutions were made by dilution of

stock solution All bacth experiments were conducted in erlenmeyer flasks on the orbital shaker (OS-3000, HACH) at the same speed (120 rpm) and temperature (27

0C) All experiments were triplicated and the mean value was determined

Investigating influential factors

In order to investigate influential factors on adsorption of phosphorous on to WHC and WHC-M800, adsorption tests were implemented by keeping varying the influential factors while keeping all other conditions the same as mentioned above The pH value of initial phosphorus concentration was varied in the range of 3-11 using H2SO4 and NaOH of various concentrations The temperature was changed

from 27 to 40 0C Adsorbent dose was varied from 0.5 to 5.0 g/ 75 mL Adsorption isotherm tests

Adsorption isotherms features were studied by varying the initial phosphorus concentration (2.5, 5, 10, 25, 50, 100, 200, 400, 500, 800, 1000 mg P/ L) After adsorption, the suspension was filtered through 0.45 µm filter paper and fitrate was used for phosphorus determination using UV-VIS Spectrophotometer (Unico, S2150UV) The adsorption amount was calculated by the difference between initial and residual concentrations The adsorption capacity at equilibrium was estimated as follows:

qe =(C0−C𝑒)

m V (2.4)

Where C0 (mg/L), Ce (mg/L), stand for the initial and equilibrium P

concentrations, respectively, V (L) and m (g) represent the volume of the solution and the adsorbent weight While adsorption tests with WHC using adsorbent dose of g/ 75 mL, the dosage of WHC-M800 was 0.5 g/ 75 mL

50

The kinetic tests were implemented with eight conical flasks Each flask containing 75 mL of the P solution of 50 mg/L was added g of WHC with the particle size of 1.4-2 mm All flasks were shaken on an orbital shaker shaker (OS-3000, HACH) at the speed of 120 rpm and temperature of 27 0C At the different

pre-determined interval times (2, 4, 6, 8, 12, 16, 20, and 24 h after the start of experiment), suspensions in flasks were filtered and the filtrate was measure to determine phosphorus level The kinetic tests with WHC-M800 were conducted with the same procedure as that of WHC However, the differences were (1) the adsorbent dose (0.5 g/ 75 mL) and (2) sampling times (0.1, 0.2, 0.5, 0.8, 1.5, 2.5 and 4.5 h after the beginning of experiment)

b Small column adsorption

All column adsorption tests were done with small columns with the height of 30 cm and diameter of cm The flowrate was adjusted by peristaltic pump (Masterflex, Cole-Parmer, HV-07554-90 USA) This study investigated three factors, which may effect on the peristaltic pump phosphorus treatment performance of the column, including (1) initial phosphorus concentration, (2) flowrate, and (3) adsorbent weight For each influential factor, two columns were run in parallel at the same conditions, except for influential factors, which were different

Effect of initial phosphorus concentration: This experiment was implemented by varying the initial phosphorus concentration (50 and 100 mg P/L) while maintaining other operation conditions the same (WHC-M800 mass of 187 g, flow rate of 10 mL/ min, temperature of 27 0C)

Effect of flowrate: In order to evaluate the effect of flowrate on the phosphorus treatment performance of two columns, the different flowrates (10 and 15 mL/min) were applied, whereas other operation conditions stayed the same (WHC-M800 mass of 187 g, flow rate of 10 mL/ min, temperature of 27 0C)

51

27 0C) to explore the influence of adsorbent mass on phosphorous removal

efficiency of columns

Figure 2.9 Small column adsorption test

c Compare removal efficiency of WHC-M800 in synthetic and real swine wastewater

In order to evaluate the effect of competing ions in the real swine wastewater on the phosphorus removal efficiency of WHC-M800, the adsorption test was carried out with both synthetic and real swine wastewater at the same adsorption conditions (initial phosphorus concentration of 53 mg P/ L, adsorbent dose of g/ 75 mL, shaking speed of 120 rpm, shaking time of 24 h, temperature of 27 0C,

solution pH of 8) After 24 h, the suspension was filtered and the filtrate was used for phosphorus analysis

2.2.4 Removal of P from synthetic wastewater using the integrated CWs- adsorption system

52

The CW units (tank 1&3), Upon passlum plants with initial height of about 25 cm were planted with the mass 560 g/ tank, and followed by adsorption unit (WHC-M800) in series

To enhance the phosphorus removal efficiency of integrated CW system, tank 1&3 were connected with the adsorption unit The two of adsorption unit made of polyethylence columns, with the height of 35 cm and the diameter of 11 cm Each column was packed with 27.5 cm of WHC-M800

Both of four tanks were operated as subsurface-horizontal flow, hydraulic retention time (HRT) of 5.4 days by using 04 peristaltic pumps Synthetic wastewater used with concentration of phosphorus and nitrogen are 12.5 mg/ L, N: 125 mg/ L, respectively

The water sample was collected daily (during month) to analyze pH values (pH meter, Mettler Toledo Seven Compact S220K), turbidity (tubidity meter, HACH, USA) as well as the P concentration (365 EPA method)

53

2.3 Analytical methods 2.3.1 Phosphorus analysis

The concentration of total phosphorus and ortho phosphorus in wastewater was determined according to the standard operating procedures (365.3-EPA method) The calibration curve was built based on the known phosphorus concentrations and their absorbances By using calibration curve and pre-determined absorbances, the unknown phosphorus concentrations were calculated

Figure 2.11 Calibration curve for phosphorus analysis

2.3.2 Other parameters analysis

Table 2.1 Analysis methods for BOD, COD, TN, NH4

Parameter Method

BOD5 TCVN 6001:2008 (ISO 5815-2:2003)

COD TCVN 6491:1999 (ISO 6060:1989)

TN TCVN 6638:2000 (ISO10048 : 1991)

NH4+ TCVN 6179 -1: 1996 (ISO 7150-1: 1984)

2.4 Data statistical analysis

Each kind of experiment was triplicated and the average value was determined The data was treated by using microsoft excel

y = 2.4886x R² = 0.9965

0 0.1 0.2 0.3 0.4 0.5 0.6

0 0.2 0.4 0.6 0.8 1.2 1.4

Abs

o

rba

nce

54

Determine physicochemical properties by using BET, SEM-EDX, FTIR machine, and pH, turbidity meter

Determine the weight loss by equation (2.1)

Determine the P adsorption capacity of materials by equation (2.4) Determine the P adsorption efficiency by equation (2.5) as follow:

Adsorption efficiency =(C0−C𝑒)

C0 ∗ 100 (2.5)

where

C0 (mg/L), the initial P concentration

55 CHAPTER

RESULTS AND DISCUSSION

3.1 Screening of filter materials for use as substrate in CWs

The substrate plays a crucial role for eliminating of phosphorus Phosphorus can be removed mainly through exchange, adsorption, and precipitation processes (Wu et al., 2015) Hence, selecting of filter materials to apply in CW is an important issue

According to Biswas (2008) and Ning et al (2008), the potential materials for P removal generally must have some characteristics such as high adsorption capacity, abundant availability, low-cost, and potential regeneration Vohla et al (2011) also reported that potential filter materials in CW should have good hydraulic conductivity, reasonable size, less side effects and high durability

In this study, to select the best potential material for use as substrate in CW, five selection criteria were applied, which include high P adsorption capacity, high hydraulic conductivity, less side effects, low-cost and abundant availability

Based on these five selection criteria, seven filter materials, which were divided into such three groups as natural materials (LA, LS, CR), industrial by-products (SS, CS WHC), agricultural by -products (OK), were investigated (see Figure 3.1 in detail)

3.1.1 Comparing potential materials based on P adsorption capacities

56

Figure 3.1 Comparison of P adsorption capacity of investigated filter materials (Ci = 200 mgP/ L, adsorbent dosage: g/ 125 mL, 24 h, 120 rpm, 27 0C)

It can be seen from the Figure 3.1, most of modified materials had P adsorption capacity higher than that of raw materials It demonstrated that the modification methods were effective to a different extent for various raw materials In previous-studies, also it was indicated that modification was good solution to enhance P adsorption capacity of materials Méndez (2011) used hydrochloric acid to modify laterite, which led to a 10-time increase in the P adsorption capacity of laterite Pengthamkeerati et al, (2008) also used hydrochloric acid and sodium hydroxide to treat fly ash Yuangsawad and Na (2011) applied high temperature to modify oyster shell

In this study, depending on nature of materials, appropriate modification method was applied For iron, aluminum oxides-rich (LA, CS, SS) and cellulose (OK) materials were used chemical treatment method to modify While Ca-rich materials (CR, LS, WHC) were used thermal treatment method to modify Modification methods were effective, P adsorption capacity was increased from raw materials with the range of 0.34 -4.08 mg/ g to modified materials with the range of 2.18-6.9 mg/ g The modification efficiency was dramatically increased for Ca-rich materials group (LS, CR, WHC) due to after thermal treatment, the less active

2.24 2.8 2.5 2.24 0.34 4.08 2.43 6.2 3.25 2.18 2.82 6.9 6.08

LA LS CR SS CS WHC OK-M

P a ds o rpt io n c a pa cit y ( m g /g ) Raw Modified Natural materials Industrial by-products Agricultural

57

calcium carbonate was converted into more active calcium oxide and calcium hydroxide, which easily combined with phosphate ion, resulting in a significant enhancement of P adsorption capacity

Table 3.1 showed the comparison in P adsorption capacity between WHC, WHC-M800 and other filter materials It can be seen that WHC and WHC-M800 possessed an adsorption capacity, which was 10 times higher than that of materials in previous studies This can be attributed to high CaCO3/CaO content in WHC and

WHC-M800 This is supported by Vohla et al., (2011) who found that P adsorption was proportional to high Ca/CaO content of the material

Table 3.1 Phosphorus adsorption capacity of different materials

Materials P sorption capacity

(mg/ g) Reference

Bauxite 0.61 Drizo et al., 1999

Zeolite 0.043 Wang et al., 2013

Vocanic 0.227 Wang et al., 2013

Broken bricks 0.594 Wang et al., 2013

Sand (I/II) 0.43/0.44 Zhu et al., 1997

Sand (I-IV) 0.13–0.29 Ádám et al., 2007

Gravel (R/G) 0.03/0.05 Mann and Bavor, 1993

WHC 4.08 This study

WHC-M 6.9 This study

3.1.2 Comparing filter materials based on their permeability

Since filter materials are used in CWs, they must have good hydraulic conductivity to avoid clogging during operation process (Vohla et al., 2011)

58

Table 3.2 Permeability constant (K) of investigated materials

Materials constant (K) (cm/ s) Permeability Reference

LA (1.4-2 mm) 0.5 This study

CS (1.4-2 mm) 3.1 This study

LS (1.5 mm) 0.6 This study

SS (1.4-2 mm) 1.0 This study

WHC (1-2 mm) 0.8 This study

WHC-M800 (1.4- 2mm) 0.7 This study

Gravel (2-4 mm) 1.0 NPTEL, 2003

Coarse sand (0.5-1 mm) 0.1 – NPTEL, 2003

Medium sand (0.25-0.5 mm) 0.1-0.01 NPTEL, 2003

It can be seen that the obtained permeability constants of investigated materials were quite high, in the range of 0.5 -3.1 (cm/ s)

In comparison with conventional materials (gravel, sand) that usually used in traditional CWs, almost investigated materials with the particle size range of 1-2 mm in this study had better good hydraulic conductivity Therefore, these materials with this size can be applied in CW without the risk of clogging

3.1.3 Comparing filter materials based on their side effects

59

a. Change in pH of the post-adsorption solution

Using filter materials as a substrate in CW may change the pH of solution into acidic condition (e.g bauxite, fly ash etc.), or alkaline condition (e.g steel slag, limestone, red mud) (Vohla et al., 2011) This may badly affect the growth of plant and aquatic animals Thus, it is necessary to evaluate the change in pH of the post-adsorption solution In order to that, pH values were measure before and after adsorption The pH of phosphorus solution before adsorption was 4.87 The results on pH of post-adsorption solution were shown in the Figure 3.2

Figure 3.2 pH of post-adsorption solutions (Ci = 200 mg P/ L, adsorbent dosage g/ 125 mL, 24 h, 120 rpm, 27 0C)

Concerning the effect on pH of post-adsorption solution, it can be classified into groups (1) Filter materials causing acidic medium (LA and LA-M) (2) Filter materials causing alkaline medium (CR-M, LS-M, WHC-M) (3) Filter material with minor influence on pH (CS, SS-m, CS-M, LS, SS, WHC, CR) The acidification of post-adsorption solution was due to high content of Al, Fe oxides in LA Beside, since LA was modified by sulfuric acid, the surface of LA might have abundant amount of H+ ions, which were released into solution during adsorption process Meanwhile, the use of modified Ca-rich materials (CR-M, LS-M, WHC-M) resulted in extremely high pH values (over 9) of post-adsorption solution That was because

0 10 12 14

60

thermal treatment led to the conversion of CaCO3 into CaO, which reacted with

H2O to form Ca hydroxides Consequently, pH was significantly increased

This side effect should be controlled to ensure the successful application of these filter materials in CWs

b. Effect on the release of heavy metals into post-adsorption solution

Although the metal oxides in materials play an important role in P removal However, heavy metals, released from materials during adsorption process, may be harmful to the growth of plant in CWs (Vohla et al., 2011)

Some trace elements (Cu, Fe) are necessary for the plant and microorganisms at low levels, but the excessive amount of these elements will negatively impact on plant, microorganisms and soil quality (Dumontet and Mathur, 1989) Hg reduced the rate of nitrogen mineralization up to 73 % in acidic soils and 32-35 % in alkaline soils, Cu reduced the mineralization capacity of 82% in alkaline soils and 20 % in acidic soils Cd, Pb, Mn also affected to nitrogenase enzyme activity in the nitrogen fixation process In addition, heavy metals are also the main reason for leaf spot disease, reducing chlorophyll activity and reducing photosynthetic products (Ngo, 2011) Therefore, to protect plants from toxicity of heavy metals, and enhance the effluent quality, it is necessary to evaluate the release of heavy metals from investigated materials

61

Table 3.3 The concentration of heavy metals released from materials

Conc (mg/ L) As Cd Cr Cu Mn Ni Pb Zn Hg Fe

LS <0,002 0,002 0,003 <0,002 0,013 0,003 0,012 0,108 <0,0002 0,79

LA 0,021 <0,002 0,006 <0,002 0,033 0,009 0,002 0,162 <0,0002 0,59

WHC-M <0,002 <0,002 <0,002 <0,002 <0,002 0,042 <0,002 <0,002 <0,0002 <0,002

WHC <0,002 <0,002 0,005 <0,002 0,005 0,011 <0,002 0,116 <0,0002 0,475

SS <0,002 <0,002 0,005 0,011 0,374 0,009 0,007 0,088 <0,0002 1,11

CS <0,002 <0,002 0,012 <0,002 0,067 0,029 0,003 0,348 <0,0002 0.104

QCVN 40/BTNMT

62

It can be observed that the concentration of heavy metals of the post-adsorption solution in this study were lower compared to permissible Vietnam standards The concentration of heavy metals released from coal slag was similar with that reported by Nguyen (2015)

Because of minor release of metals, the investigated filter materials can be used as substrates in CW with no harmful effect on the environment

3.1.4 Selection of potential filter materials

63 Score obtained by addition as follows:

P-removal capacity: = low; = medium; = high Permeability: = medium; = good

Side effects: = Medium, = No

Availability: = Low; = Medium; = High Cost: = Medium; = Low

“-“ Lack of experiment

“**”, “*” selection criteria with the weight of and respectively Other selection criteria with the weight of because of less importance than two above selection criteria

Table 3.4 Summary of the obtained scores for investigated

Material P

removal** Permeability*

Side

effects Availability Cost Score

LA 2 15

LA-M - 1 13

LS 17

LS-M - 1 12

CR - 2 12

CR-M - 1 12

WHC 9 4 2 3 2 20

WHC-M 17

CS 2 13

CS-M - 1

SS 2 16

SS-M - 1

64

Due to the time limitation and limited supply of investigated filter materials, in this study, the permeability was determined for only few materials, including LA-M, CS-LA-M, SS-LA-M, CR, CR-LA-M, OK-M

It can be seen from the Table 3.4 that most of industrial by-product materials (CS, SS, WHC) were potential for use a substrate in CW to enhance the elimination phosphorus, because of high P adsorption capacity, high permeability, low cost This result was in consistent with statement of Biswas (2008) about the new trend to use adsorptive materials to enhance P removal by CWs Among them, WHC can meet all selection requirements, with highest score The recycling of WHC as P adsorbent helps not only to clean water environment but also to reduce the environmental burden caused by WHC as the solid waste In addition, it creates the additional value for WHC Thus, WHC was selected for further investigation later

3.2.Intensive investigation of the selected filter materials – WHC

In order to properly evaluate the applicability of WHC and WHC-M800 as the substrate in CWs, this section intensively investigated WHC in aspects of characteristics, isotherms, and kinetics and column test Before that the optimal modification conditions of WHC were identified

3.2.1 Identification of the optimal modification conditions of WHC

In order to further enhance the P adsorption capacity of raw WHC, the modification using high temperatures was implemented According to Zang et al., 2013, under high temperature, CaCO3 in raw WHC was turned into CaO, which was

more active in reaction with PO43- anions, and thus lowering P concentration in the

wastewater

In order to identify the optimal modification condition, three calcination temperature (750, 800, and 850 0C) and three calcination time (1, 2, h) were

65

Table 3.5 Effect of calcination temperature

Temperature (0C) 750 800 850

q (mg/ g) 12 18.7 20

Weight loss after

calcination (%) 3.27 4.37 11

Weight loss after

adsorption (%) 2.0 3.0 10.6

Figure 3.3 Images of raw WHC and WHC modified at different temperatures It can be observed that the P adsorption capacity of modified WHC increased with an elevation in the calcination temperature Specifically, the q value grew from 12 to 20 mg/ g when the calcination temperature increased from 750 to 850 0C This

can be explained that the conversion of CaCO3 into CaO was more complete at

higher calcination temperature (Zang et al., 2013)

66

indicated that the higher the calcination temperature was, the greater the weight loss of WHC was observed Specifically, the weight loss during calcination was increased from 3.27 to 11% when calcination temperature increased from 750 to 850 0C Similar trend occurred with the weight loss during adsorption, which

increased by 8.6% in the same temperature range as above Taking into consideration of both q value and weight loss, 800 0C was selected as the best modification temperature

After the best calcination temperature was identified, the WHC was modified at this temperature for different periods of time (1, 2, h) to determine the optimal calcination time The results were shown in Table 3.6 It was found that the weight loss of WHC was quite similar at different calcination temperatures However, the q value was significantly improved from 9.9 to 18.7 mg/ g when the calcination time increased from to 3h Therefore, h was selected as the best calcination time In short, thermal treatment at 800 0C for 3h was considered as the optimal modification condition

Table 3.6 Effect of the calcination time

Calcination time (h) 1h 2h 3h

q (mg/ g) 9.3 9.9 18.7

Weight loss (%) 4.1 5.7 6.1

3.2.2 Physicochemical properties

BET results

67

Table 3.7 Brunauer Emmett Teller (BET) analysis Sample BET surface area

(m2/ g)

Pore volume

(cm3/ g) Pore size (nm)

WHC 0.1294 0.00002 2.1041

WHC-M800 0.0948 0.00002 1.7129

The Table 3.7 showed that modification of WHC (8000C, 3h) led to a reduction in both surface area and pore size The surface area was decreased from 0.1294 to 0.0948 m2/ g and the pore size was decline from 2.1041 to 1.7129 (nm) The pore volume was changed marginally This can be explained by the fact that the calcium carbonate was decomposed due to the high temperature This caused the refining of the particle At 800 0C, the lattice distortion among the grains of calcium oxide led to the reconstruction of lattice atoms and reduction of the space among molecules (Zhang and Chen, 2013) It was well recognized that the surface area as well as pore size of materials play a decisive role in physisorption In this study, in spite of the reduction in these parameters, WHC-M800 exhibited the improved adsorption capacity This proves that physisorption was not the main mechanism for the retention of P by WHC-M800 In other words, chemisorption might be dominant in this case

SEM- EDX results

68

Table 3.8 Elemental content of WHC

Element Atomic %

C 38.18

O 37.59

Al 1.29

Si 2.02

Ca 3.28

Fe 0.46

N 15.86

Mn 0.24

S 0.59

Figure 3.6 EDX spectrum of WHC

Table 3.9 Elemental content of WHC-M800 Element Atomic %

O 61.59

Ca 11.82

C 17.63

Na 0.95

N

Cl 0.17

Cu 0.1

S 0.03

F 0.57

Figure 3.7 EDX spectrum of WHC-M800

SEM observation was recorded and displayed in Figures 3.4 & 3.5 It was found that the variation in morphology of WHC after modification Specifically, more CaO crystals with smaller particle size could be found on the surface of WHC-M800 compared to raw WHC

69

WHC 8.54 and 24 % for oxygen and calcium respectively The increase in the percentage of oxygen and calcium elements can be attributed to a decrease in proportion of carbon as the result of conversion of CaCO3 into CaO As observed

from the Table 3.8 & 3.9 the atomic percentage of C was decreased from 38.18 to 17.63%

FTIR results

Figure 3.8 FTIR analysis for WHC

Figure 3.9 FTIR analysis for WHC WHC-M800

70

the laboratory of Faculty of Chemistry, VNU University of Science (HUS) The spectrum was recorded in the range of (4000–400) cm-1

The spectrum for WHC was shown in Figure 3.8 Accordingly, the peaks at 712, 859, 1082, 1476 cm-1 were dominant, indicating the presence of carbonate

groups in the materials The Figure 3.9 represented the spectrum of WHC-M800 It was found that WHC-M800 had the same peaks of CO32− band at 712, 874, 1082,

1421 cm−1 However the intensity of these peaks were smaller than that of WHC This may be due to the loss of CaCO3 in the form of CO2, as the result of thermal

decomposition The same findings were reported by Kim et al (2018) and Khiri et al (2016)

Accoriding to Khiri et al (2016), the peak at 3641cm−1 represented for –OH bond group This peak could be found in the spectra for both WHC and WHC-M800 However the peak intensity of WHC-M800 was higher This is explained by the fact that in WHC-M800, Ca existed mainly in the form of CaO, which could adsorb H2O easier than CaCO3 in WHC to form OH- groups (Khiri et al, 2016; Loy

et al., 2016) The resuls implied that WHC-M800 shoud be kept in a tight glass bottle to avoid the undesirable adsorption of water vapor, hindering the adsorption characteristis of the material

3.2.3 Batch experiment

a. Investigating influential factors

71 Figure 3.10 Effect of pH of WHC on phosphorus removal (Ci = 50 mg/ L, adsorbent dosage 3g/75 mL, 24 h, 120

rpm, 27 0C)

Figure 3.11 Effect of pH of WHC-M800 on phosphorus removal (Ci = 50 mg/ L, adsorbent dosage 0.5g/75 mL, 0.5h, 120

rpm, 27 0C)

In adsorption, pH plays an important role in P adsorption capacity That is because the ionization of active functional groups on sorbent surfaces and the speciation of phosphorus are affected by pH (Wang et al., 2015) Thus, this experiment was implemented to determine the effect of pH on to P removal efficiency of WHC and WHC-M800 This will provide useful information for preparing the simulated wastewater as the influent of CW

In this study, five pH values (3; 5; 7; 9; 11) were investigated for both WHC and WHC-M800 The obtained results were shown in Figure 3.10 and Figure 3.11

For WHC, it can be observed that WHC has highest P removal efficiency at pH value of 3, which reached up to 96 % with the P adsorption capacity was 1.52 mg/ g The Figure 3.10 showed that the P removal efficiency decreased with increasing pH values until pH = The P removal efficiency was declined from 96.08 to 86.43% when pH increased from to The P removal efficiencies at pH (59.81%) and pH 11 (59.90%) were much lower than that at pH (96.08%) This

0 10 12 20 40 60 80 100 120

3 11

Fi n a l p H % P re m o v a l Initial pH %P removal Final pH 12 15 20 40 60 80 100 120

3 11

72

result was in line with that reported by Agyeia et al (2002), who indicated that the phosphorus removal was best in acidic medium It can be explained by two mechanisms This can be explained by the fact that H+ cations were attached to the surface of WHC via Ca, Mg hydroxide This creates a secondary positive layer to bind the negative orthophosphate The second possibility was the acidic medium could enable WHC to release more positive Ca2+ cations into solution to react with negative PO43- to form precipitation of Ca3(PO4)2 In the contrary, at pH and pH

11, the P removal efficiency was low This was because the alkaline medium resulted in the formation of a negative OH- layer on the surface of WHC As the result of electrostatic repulsion force, the retention of negative PO43- ions by WHC

was diminished (Agyeia et al.,2002)

For WHC-M800, the same trend occurred as with WHC in the pH range of 3-7 However, the P removal efficiency of WHC-M800 was sharply increased with increasing pH in the pH range of 9-11, reaching 98.24% just in 0.5h This can be attributed to the dominance of precipitation over the adsorption as the P removal mechanism The precipitate was formed by the reaction of Ca2+ ions, which were

released from thermally modified WHC, with PO43- in the solution This is

confirmed by the observation of a thick layer of the white precipitate at the bottom of conical flasks

73

Effect of adsorbent dosage on phosphorus removal

Figure 3.12 Effect of dosage of WHC on phosphorus removal (Ci = 50 mg/ L, 24h,

120 rpm, 27 0C)

Figure 3.13 Effect of dosage of WHC-M800 on phosphorus removal (Ci = 50

mg/ L, 0.5h, 120 rpm, 27 0C)

Figure 3.12 and Figure 3.13 showed the effect of adsorbent dose on P removal efficiencies and P adsorption capacity of WHC and WHC-M800 It can be observed that the P removal efficiencies of both WHC and WHC-M800 were proportional to the adsorbent dose P removal efficiencies increased from 4.56 to 87.55% and from 50.52 to 99.9% for WHC and WHC-M800 respectively with increasing adsorbent dose from 0.5 to 5g/ 75 mL This can be explained that more adsorption sites were available at higher adsorbent dose (Molle et al (2002) The same trend was reported by Deng and Wheatley (2018)

In contrast, the P adsorption capacity of WHC was found to decline with increasing adsorbent dose P adsorption capacity of WHC decreased from 1.12 to 0.788 mg/ g with increasing adsorbent dose from to g/ 75mL and decline from 4.51 to 0.9 mg/ g with the rise of adsorbent dose from 0.5 to g/ 75mL for WHC-M800 It can be explained by the fact that the higher adsorbent dose resulted in a

0 20 40 60 80 100 120 0.2 0.4 0.6 0.8 1.2 1.4

0

P re m o v a l (%) P a ds o rpt io n c a pa cit y ( m g /g )

Adsorbent dosage (g)

P adsorption capacity (mg/g) % P removal

0 20 40 60 80 100 120

0

P re m o v a l (%) P a ds o rpt io n c a pa cit y ( m g /g )

Adsorbent dosage (g)

74

greater number of adsorption sites on the surface of materials However, the number of orthophosphate anions in the solution was limited When all phosphate anions in the solution were captured by some adsorption sites, the increase in adsorption sites as the result of adsorption dose could not enhance the P uptake anymore (Deng and Wheatley, 2018)

Effect of temperature on phosphorus removal

The P adsorption capacity of material also depends on the temperature In this study, four temperatures (27 0C; 30 0C; 35 0C; 40 0C) were performed for both

WHC and WHC-M800 The obtained results were shown in Figure 3.14 and Figure 3.15

Figure 3.14 Effect of temperature of WHC on phosphorus removal (Ci = 50 mg/ L, adsorbent dosage: 3g/75 mL 24h, 120 rpm)

Figure 3.15 Effect of temperature WHC-M800 on phosphorus removal (Ci = 50 mg/ L, adsorbent dosage: 0.5g/75 mL

0.5h, 120 rpm,)

It can be observed that temperature affected to the phosphorus removal efficiency of both WHC and WHC-M800 The eliminating phosphorus efficacy increased with increasing temperatures This result is similar to the report of Cucarella and Renman (2009) Additionly, Agyei et al (2002) also indicated that P

0.0 0.4 0.8 1.2 1.6 2.0 20 40 60 80 100

27 30 35 40

P a ds o rpt io n c a pa cit y ( m g /g ) P re m o v a l (%) Temperature (°C) %P removal q (mg/g) 0.0 0.5 1.0 1.5 20 40 60 80

27 30 35 40

75

sorption of fly ash and furnace slag were significantly increased with high temperatures Ramprasad et al (2017) also released that in the summer with high temperature, the phosphorus removal rate was higher than that in other seasons This trend is line with report of Ugurlu and Salman (1998)

The P removal efficiency increased with rise in temperatures, this can be explained by the high temperatures have created new active sites, results in the increasing phosphorus ions into micropores of WHC, WHC-M800 (Al-Degs et al., 2008) The results also indicate that this adsorption process had an endothermic nature

b. Adsorption isotherm test

In order to determine isotherm parameters and the most appropriate isotherm model, the experimental data were fitted with Langmuir, Freundlich model Langmuir model represents to monolayer adsorption, assuming that adsorption takes place at a specific number of adsorption sites, each site is occupied by one adsorbate molecule, all sites are the same, and there is no interaction between adsorbed molecules Langmuir isotherm model in the nonlinear form (Kumar et al., 2010) is given as follow:

qe =qmKLCe

1+ KLCe (3.1)

where qm (mg/ g) is the maximum mass of phosphates adsorbed per unit

weight of material when the surface of material is entirely covered by monolayer of phosphate ions, KL (L/ mg) is Langmuir constant associated with the affinity of

binding sites on material

The linear Langmuir adsorption isotherms are presented in Figure 3.18 and Figure 3.20 The values of qm and KL of linear expression of Langmuir adsorption

76

1 q𝑒 =

1 qm +

1

KLqmCe (3.2)

The Freundlich model represents non-ideal adsorption, with multi adsorption sites and heterogeneous surfaces It based on the assumption that active binding sites are occupied first, and the binding ability declines with an increase in the site occupation Freundlich isotherm model in the nonlinear form (Boujelben et al., 2008) is expressed by the equation (3.3) as follow:

qe = Kf(Ce)1/n (3.3)

where

Kf (L/ g), stand for indicating the adsorption capacity

N, stand for adsorption intensity

Equetion (3.3) can be rearranged to obtain a linear form by taking logarithms as follow:

lnqe = ln Kf +

1

𝑛 lnCe (3.4)

They were shown that the plot of ln qe and ln Ce yields two straight lines (Figure

77 Figure 3.16 The fitting of isotherm

models to P adsorption onto WHC

Figure 3.17 The fitting of isotherm models to P adsorption onto WHC-M800

Figure 3.18 Linear form of adsorption isotherm following Langmuir of WHC

Figure 3.19 Linear form of adsorption isotherm following Freundlich of WHC

3 12

0 200 400 600 800 1000

qe( m g /g ) Ce (mg/L) Experimental data Langmuir model Freundlich model 15 30 45

0 200 400 600 800 1000

qe( m g /g ) Ce(mg/L) Experimental data Langmuir model Freunlich model 0.07 0.22 0.37 0.52

0 0.02 0.04 0.06

1 /qe 1/Ce 2.5 5.5

0.9 1.4 1.9 2.4

ln

(q

e

)

78

Table 3.10 Langmuir and Freundlich adsorption isotherm constants

Sample

Langmuir model Freundlich model

qm (mg/ g) KL (L/ mg) R2 n Kf R2

WHC 11.6 0.014 0.9976 2.59 0.88 0.8843

WHC-M800 39.04 0.02 0.9983 3.68 6.4 0.927

As can be seen in the Table 3.10, the correlation coefficients (R2) of WHC for Langmuir, Freundlich models were 0.997 and 0.8843 respectively And the correlation coefficients (R2) of WHC-M800 were and 0.998 and 0.927 respectively

Through the correlation coefficient values R2, it can be concluded that the

experimental data of both WHC and WHC-M800 better fitted the Langmuir model than the Freundlich model as the R2 values of Langmuir model tend to be much

closer to than those obtained from the Freundlich isotherm Therefore, the adsorption can be described as monolayer and the Langmuir theoretical monolayer sorption capacity for WHC and WHC-M800 were 11.6 (mg/ g) and 39.04 (mg/ g) respectively

Figure 3.20 Linear form of adsorption isotherm following Langmuir of

WHC-M800

Figure 3.21 Linear form of adsorption isotherm following Freundlich of

WHC-M800 0.025

0.035 0.045

0.001 0.005 0.009 0.013

1

/qe

1/Ce

4.4 5.4 6.4 7.4

3.06 3.26 3.46 3.66 3.86

lnqe

79

The high correlation coefficient values (R2) also shown that the WHC and

WHC-M800 are potential adsorbents for P removal from wastewater

c. Kinetic test

Kinetic study plays a key role in adsorption, due to it can provide information about adsorption rate as well as indicate adsorption mechanism (Nguyen et al, 2012)

Figure 3.22 Kinetic test of WHC Figure 3.23 Kinetic test of WHC-M800 As can be observed from the Figure 3.22 and Figure 3.23, the P adsorption rate and eliminating P efficacy increased till equilibrium of WHC and WHC-M800 For WHC, the P removal efficiency was reached at 80 % after 12 h and 90 % at 26 h with adsorbent dosage of g/ 75 mL For WHC-M800, it was reached at 95 % after 1.5 h and 99 % at 2.5 h only with small adsorbent dosage of 0.5 g/ 75 mL

BET results shown that after calcination both surface area and pore volume and size of WHC are reduced However, the kinetic results indicated that WHC-M800 has high speed of adsorption Therefore, physisorption plays a very small role in WHC-M800, whereas chemisorption is dominant

0.0 0.5 1.0 1.5 2.0 2.5 20 40 60 80 100

2 12 16 20 26

q ( m g /g ) P re m o v a l (%) Time (h) P removal q 12 20 40 60 80 100

0.1 0.2 0.5 0.8 1.5 2.5 3.5 4.5

80

This result was implemented with P initial concentrations of 50 mg/ L With the adsorption rate were presented in Figure 3.22, WHC demonstrated that it can reached likely adsorption rate as in CWs system With high adsorption rate, WHC-M800 can be used to enhance P removal as an adsorption unit after CWs system

3.2.4 Column experiment

For batch experiment, only the amount of small wastewater can be treated (Damte, 2006) Although P adsorption capacity might be gotten from batch equilibrium isotherm tests, this result could not be applied in continuous flow fixed-bed, because the continuous flow in column usually have shorter contact time than the equilibrium time as discussed by Nguyen et al, 2015 Whereas, the column experiment is benefit, the large volume of wastewater can be treated by the dynamic adsorption systems Besides, the column breakthrough curve may provide dynamic adsorption capacity (Nguyen et al, 2015)

The column test aims to evaluate the effect of different operating variables (flowrate, the amount of materials, initial concentration) on P treatment performace, to estimate the dynamic adsorption capacity of WHC-M800, and to scale-up the WHC-M800 packed bed column adsorption system

81 Figure 3.24 Breakthrough curve of WHC-M800 for P removal under the different flowrate (Ci=50mg/ L, 187g)

Figure 3.25 Breakthrough curve of WHC-M800 for P removal under the different initial concentration (Q=10mL/ min, 187g)

Table 3.10 P adsorption capacity at different conditions

Q (mL/min) P adsorption capacity

(mg/g)

10 11.4

15 10

Dosage(g)

100 11

50

Ci (mg/L)

50 12

100 6.4

Figure 3.26 Breakthrough curve of WHC-M800 for P removal under the different

weight of material (Ci=50 mgP/L, Q=10mL/ min) 0.2 0.4 0.6 0.8

0 2000 4000 6000 8000

Ct /Co Time (min) Q=10mL/min Q=15mL/min 0.2 0.4 0.6 0.8

0 2000 4000 6000 8000

Ct /Co Time (min) Ci=100mg/L Ci=50mg/L 0.2 0.4 0.6 0.8

0 1000 2000 3000 4000

Ct

/Co

Time (min)

82

The breakthrough curve of each column was identified by plotting the Ct/

C0 (C0 and Ct are the P concentration of influent and effluent respectively)

When Ct/ C0= 0.95, the column can be considered to reaching saturation state

(Suksabye et al., 2008)

It can be observed from the Figure 3.25, 3.26 and Figure 3.27 The shape of the breakthrough curve is saturated earlier at lower volume of material, higher flow rates and P initial concentration It may be explained by the fact that the bigger volume of materials, and lower flowrate, and lower initial concentration results in longer contact time, more the phosphorus ions were kept in the column Consequently, the P removal efficiency is better This result agreed with findings of Nguyen et al (2015) and Zhang et al (2014)

In addition, the maximum P adsorption capacities of WHC-M800 for three different conditions are shown in the Table 3.10 The maximum P adsorption capacity in column test reached around 12 (mg/ g), it is lower than the maximum P adsorption capacity in isotherm test (39.04 mg/ g) Therefore, it concluded that the isotherm studies overestimated the P removal capacity of WHC-M800, and column studies demonstrated P adsorption capacities with the reasonable values Column experiments might better simulate the condition of actual CWs (e.g substrate layer, soil–water ratio, and feeding mode influent ) (Zang et al., 2014)

3.2.5 Comparing the P removal efficiency of WHC-M800 in the synthetic and real

swine wastewater

83

only contained 53 mg/ L of phosphorus The obtained results were shown in the Figure 3.28

In this experiment, real swine wastewater is characterized by some parameters in Table 3.11

Table 3.11 Parameters of real post-biogas swine wastewater in Chuong My, Hanoi

Parameter TN (mg/L)

NH4+

(mg/L) ortho-P (mg/L) TP (mg/L) BOD5 (mg/L) COD

(mg/L) pH

Turbility (NTU)

Conc 729.75 571 52.9 151 299.3 1557.9 8.06 748

Figure 3.28 P adsorption capacity of WHC-M by real wastewater and synthetic wastewater

It can be observed in Figure 3.28 WHC-M800 obtained high P removal efficiency with real swine wastewater (80%) However it is still lower than P removal efficiency by synthetic wastewater (99%) at the same initial concentration This can be explained that in real swine wastewater exist other anions that can compete with phosphorus

3 11 13 20 40 60 80 100 120

Synthetic wastewater Real wastewater

pH % P removal

84

Although, P removal efficiency with real swine wastewater is lower than synthetic wastewater, but it has lower pH value (around 8) compared to that (around 12) in synthetic wastewater This may be explained by the fact that in real swine wastewater has buffer zone (NH4+/NH3; CH3COO-/CH3COOH) that keep stably pH

This is a key finding to prepare synthetic wastewater for using in CW system

3.3 The P treatment performance in the integrated CWs – adsorption system

The main purpose of this experiment was to compare P removal efficiency by CW with the substrate was WHC (adsorptive material) and yellow sand (conventional material) In addition, the contribution of CW unit (plant, substrate) and adsorption unit was also evaluated

In this study, the WHC was used at the range size of (0.6-2 mm) as main layer (23 cm) and the range size of (1.4 - mm) as small bottom layer (4.5 cm) Due to the producing material process, the range size of (0.6-2 mm) was dominant whereas the amount of volume at range size (1.4 - mm) was very small Moreover, the range size of (0.6-2 mm) could be ensured to minimize clogging

85

Figure 3.29 The change of phosphorus in the effluent over the time

Table 3.12 The phosphorus concentrations before and after treatment with horizontal flow lab-scale constructed wetlands

Wastewater

sampling point Tank Tank Tank Tank

Before treatment 12.1 (10.89-13.25) 12.1 (10.89-13.25) 12.1 (10.89-13.25) 12.1 (10.89-13.25) After the CWs 0.24

(008-0.46) 0.47 (0.11-0.85) 2.79 (0.84-5.25) 3.21 (0.84-6.6) After the adsorption unit 0.16

(0.09-0.18) -

0.6

(0.1-1.35) -

0 12

10-May 15-May 20-May 25-May 30-May 4-Jun 9-Jun

P c o n ce n tr ation (m g P/ L)

Date of sampling

Tank2 Tank1 Tank3 Tank4 Adsorption unit Adsorption unit

Average initial concentration (12.1mgP/ L)

86

Table 3.13 The phosphorus removal efficiency and pH after treatment with horizontal flow lab-scale constructed wetlands

Wastewater sampling

point

Tank Tank Tank Tank Adsorption unit

Adsorption unit P removal

efficiency (%)

98 96.1 77 73.6 98.7 95

pH 8.1 8.1 7.7 7.8 8.7 8.6

The CW system was operated during 29 days The basic difference between the phosphorus removal efficiency of WHC and yellow sand was found

In the small-scale, using WHC as substrate had the average phosphorus removal efficiency 21 % higher than using yellow sand as substrate In the initial stage, the difference in eliminating phosphorus efficiency of both WHC and sand was insignificant, but the longer time, the difference is obvious Because the P adsorption capacity of WHC (11.6 mg/ g) was much higher than P adsorption capacity (0.13 mg/ g) of sand (Ádám et al., 2007) resulted in the saturation of sand was faster

After one month operation, the P concentration in effluent of CW based on WHC (0.24 mgP/ L) was far below Vietnamese effluent discharge standards (6mgP/ L), and still represented a stable trend whereas the P concentration in effluent of CW based on yellow sand was increase rapidly, it reached over Vietnamese effluent discharge standards

87

The use of adsorption column with WHC-M800 as a polishing unit could keep P removal efficiency up to 98.7 % after tank and 95 % after tank

In addition, Ubon paspalum plant also contributed to the phosphorus removal processes in CW system by consuming nutrient for their growth (Cooke, 1992) However its contribution was low (1.9-3.5 %) because this was the adaptation stage of plants in CW system

In comparison at the tank and tank 3, the contribution of plant at tank (3.5 %) was slightly higher than tank (1.9 %), however the pH at the tank (7.7) was lower than that of tank (8.1) According to Cerozi and Fitzsimmons (2016), the plants has good uptake at the range pH 5.5 - 7.5 Therefore with the pH at the tank was higher than those of tank might be caused to this difference of plant uptake

88 CHAPER

CONCLUSION AND RECOMMENDATION

4.1 CONCLUSION

This study has selected potential filter material (WHC), intensively investigated the selected material, and evaluated the trial application of WHC for P removal in CWs The key findings can be summarized as follows

(1) WHC was superior to other investigated materials for use as substrate in CW (2) WHC and WHC-M800 possessed suitable physicochemical properties for use as substrate in CW The maximum P adsorption capacity of WHC-M800 (39.04 mg/g) was significantly higher than that of WHC (11.3 mg/g) Batch experiments indicated that WHC and WHC-M800 could work effectively in a wide range of pH (3-11) Isotherm data was best fitted by the Langmuir model with high R2 values (0.996 and 0.994 for WHC and WHC-M800) The kinetic and column test showed the high P removal efficiency for both WHC and WHC-M800 WHC-M800 obtained high removal efficiency with real swine wastewater (80%)

89

4.2 RECOMMENDATION

In this study, the hybrid CW-adsorption treatment system has been operated for a short period of time with only one hydraulic and P loading regime Thus, the optimal operation conditions and P mass balance should be the focus of the future work

This research was conducted mainly with synthetic wastewater In the future research, the treatment performance of the CW-adsorption system should be evaluated with real swine wastewater

This study focused only on P removal efficiency of WHC and WHC-M800 The additional study should perform to investigate the simultaneous removal of several pollutants (organic, TSS, P and N)

90

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Internet

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APPENDICES

a) CW system in Higashikagura,

Hokkaido b) CW system in Biei, Hokkaido

c) CW system in Mombetsu, Hokkaido

d) Pilot scale CW system in Koka, Shiga

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a) Dumping site of WHC shell b) Sampling swine wastewater

c) Collecting WHC shell d) Packing sample

110

a) Setting CWs b) CW after day of operation

c) Wastewater sampling d) CW after 17 days of operation

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