The behavior of humic substance in iron electrolysis process and its influence on phosphorus removal

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY HA THI DIEP ANH THE BEHAVIOR OF HUMIC SUBSTANCE IN IRON ELECTROLYSIS PROCESS AND ITS INFLUENCE ON PHOSPHORUS REMOVAL MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY HA THI DIEP ANH THE BEHAVIOR OF HUMIC SUBSTANCE IN IRON ELECTROLYSIS PROCESS AND ITS INFLUENCE ON PHOSPHORUS REMOVAL MAJOR: ENVIRONMENTAL ENGINEERING CODE: 8520320.01 RESEARCH SUPERVISOR: Prof Dr JUN NAKAJIMA Associate Prof Dr LE VAN CHIEU Hanoi, 2020 ACKNOWLEDGMENT First and foremost, I would like to sincerely thank my instructor, Prof Jun Nakajima for helping and always encouraging me, because of his patience, motivation, and immense knowledge His generosity and devoted guidance contributed greatly to my dissertation completion and developed myself There is no unmatched honor to work with him Second, I would like to thank my co-supervisor, Associate Prof Dr Le Van Chieu a lot because of his thoughtfulness and kindness He is always enthusiastic about reading and revising my research carefully Third, I would like to express my sincere thanks to all MEE Department for your valuable support in the process of implementing the thesis as well as my stay at VJU And I would also like to thank JICA for its support Thanks for all that we have been through together I would like to express my appreciation to all Ritsumeikan University professors, staff, and doctors, for their warm and enthusiastic welcome during my internship They gave me access to labs and research facilities Without their valuable support, it would not be possible to this research Finally, I would like to thank my family and friends who have supported me spiritually throughout the process of writing this thesis in particular, and my life in general Hanoi, August 7th, 2020 Ha Thi Diep Anh i TABLE OF CONTENT ACKNOWLEDGMENT i INTRODUCTION .1 Background .1 Objectives 3 Structure of thesis CHAPTER LITERATURE REVIEW 1.1 Phosphorus removal technologies 1.1.1 Phosphorus (P) pollution 1.1.2 Phosphorus removal technologies 1.2 Electrocoagulation/Iron electrolysis .15 1.2.1 Definition 16 1.2.2 Advantages and drawbacks of EC 17 1.2.3 The principle of electrocoagulation 18 1.3.4 Application of EC 19 1.3 Iron electrolysis application for phosphorus removal in Johkasou systems 19 1.3.1 Johkasou systems for decentralized domestic wastewater treatment 19 1.3.2 Phosphorus removal in Johkasou and application of iron electrolysis 20 1.3.3 Interference of phosphorus removal using iron electrolysis 23 1.4 Humic substance 24 1.4.1 General description 24 1.4.2 Chemical characteristic 26 CHAPTER MATERIALS AND METHODOLOGY 28 2.1 Materials .28 2.1.1 Synthetic test liquor (phosphate solution) .28 2.1.2 Humic substance sample liquor 28 2.1.3 Humic acid sample liquor .29 2.2 Iron electrolysis experiment set-up .30 2.3 Operational condition of experiment 31 2.3.1 Iron electrolysis with or without oxygen supply 31 2.3.2 Iron electrolysis with HS addition 32 2.3.3 Iron electrolysis with humic acid addition 33 2.4 Chemical analysis .34 2.4.1 Suspended solid (SS) .34 2.4.2 Iron analysis .35 2.4.3 Phosphorus analysis (PO4-P) 36 2.5 Fluorescence spectroscopy analyses by three-dimensional excitation-emission matrix 36 CHAPTER RESULTS AND DISCUSSION .38 3.1 Iron electrolysis without oxygen supply .38 ii 3.1.1 Iron electrolysis with aeration 38 3.1.2 Iron electrolysis without aeration .39 3.1.3 Discussion .41 3.2 The effect of humic substance on iron electrolysis 43 3.2.1 Iron coagulation decrease by humic substance addition 43 3.2.2 Decrease of phosphorus insolubilization by iron coagulation decrease 44 3.2.3 Discussion 45 3.3 The effect of fulvic acid to iron electrolysis 47 3.3.1 Iron electrolysis with humic acid addition 47 3.3.3 Discussion .50 CONCLUSION 52 REFERENCES 53 iii LIST OF TABLES Table 1.1 Vietnam national technical regulations on effluent discharge Table 2.1 Preparation of synthetic test liquor 28 Table 2.2 Operational experiment condition 32 Table 2.3 Preparation chemicals to iron analysis 35 Table 2.4 Preparation chemicals to phosphorus analysis 36 Table 3.1 Effluent parameters after electrolysis performed in aeration condition 38 Table 3.2 Effluent parameters after electrolysis performed in humic substance addition experiment 43 Table 3.3 Effluent parameters after electrolysis performed in humic acid addition experiment 47 i LIST OF FIGUREURES Figure Iron electrolysis reactor (Fayad, N (n.d.)., 2017) .2 Figure Structure of thesis Figure 1.1 Changes in structure of phosphorus compounds in municipal wastewater between year 1971 and 1991 (Rybicki, n.d.) Figure 1.2 Phosphorus removal technologies Figure 1.3 One – point chemical addition 10 Figure 1.4 Two – point chemical addition 10 Figure 1.5 Metabolic pathway of PAO under aerobic and anaerobic conditions (Bunce et al., 2018) 14 Figure 1.6 Iron electrolysis principle 18 Figure 1.7 Combination process of BOD and nitrogen removal type Johkasou and phosphorus adsorption column (Ebie et al., 2008) 22 Figure 1.8 Johkasou for phosphorus – BOD – Nitrogen removal (Kumokawa, n.d.) 23 Figure 1.9 Hypothetical humic acid structure according to Stevenson (1982) .26 Figure 1.10 The hypothetical model structure of fulvic acid (Buffle's model) .26 Figure 1.11 Chelation of Cu and Zn in top examples with simple complexation of Zn by an amino acid (Hd, n.d.) 27 Figure 2.1 The map of Hanoi and Nam Son landfill .29 Figure 2.2 Humic acid, Nacalai Tesque, Japan 29 Figure 2.3 Schematic diagram of the laboratory-scale experiment 30 Figure 2.4 The types of equipment used to set-up experiments 30 Figure 2.5 Synthetic test wastewater preparation 31 Figure 2.6 Set – up experiments 32 Figure 2.7 Humic substance experiment set-up 33 Figure 2.8 Humic acids addition experiment set-up .34 Figure 2.9 Procedure iron calculate 34 Figure 10 Fluorescence Spectrophotometer F-7000 (Hitachi, Tokyo, Japan) 37 Figure 3.1 Phosphorus insolubilization 39 Figure 3.2 Iron coagulation ……………………………………………… 39 Figure 3.3 Iron coagulation (without aeration) .39 Figure 3.3 Iron coagulation (without aeration) .39 Figure 3.4 Iron coagulation (N2 gas bubbling) 39 Figure 3.5 Iron coagulation under aerobic condition (a) and anaerobic condition (b)………………………………………………………………………………… 37 Figure 3.6 Phosphorus insolubilization (without aeration)……………………… 41 Figure 3.7 Phosphorus insolubilization (N2 gas bubbling) 41 Figure 3.8 The existing pathway models 41 Figure 3.9 The new pathway model including ferrous compound coagulation 42 ii Figure 3.10 Iron coagulation (Humic substance addition) 44 Figure 3.11 Phosphorus insolubilization (HS addition) 45 Figure 3.12 Molar ratio of ΔFe / ΔP .46 Figure 3.13 Soluble complex formation of ferrous ion and HS 47 Figure 3.14 Iron coagulation (Humic acid addition) .48 Figure 3.15 Phosphorus insolubilization (HA addition) 49 Figure 3.16 EEMs Fluorescence spectra of humic substance sample (leachate sample) 49 Figure 3.17 EEMs Fluorescence spectra of humic acid sample .50 Figure 3.18 The effect of fulvic acid on iron electrolysis 51 iii LIST OF ABBREVIATIONS BOD Biochemical oxygen demand DC Direct current DOC Dissolved organic carbon EBPR Enhanced biological phosphorus removal EC Electrocoagulation EEM Excitation emission matrix FDOM Fluorescent dissolved organic matter HA Humic acid HS Humic substance MBR Membrane bioreactor PAO Phosphorus accumulation organisms SBR Small-scale wastewater treatment plants SWTPs Sequencing batch reactor SS Suspended solids TDS Total dissolved solid WWTP Wastewater treatment plant iv INTRODUCTION Background Some serious environmental problems such as eutrophication are due to the direct discharge of phosphorus into the water source The abundance of these nutrients will spur the development of algae, mosses, and mollusks in the water and will ultimately affect the biological balance of water In addition, phosphorus is also a limited resource, so we need to remove and recover P effectively from wastewater before discharging it into the water source In order to remove phosphorus from wastewater sources, there are several methods being applied, including adsorption, chemical precipitation (using metal salts), biological processes, and ion-exchange methods ion (Omwene et al., 2018) Among the methods in the two most used methods are chemical precipitation and biological processes Chemical precipitation and adsorption are currently the best methods for efficiency By adding metal salts (aluminum salts or iron salts) most of the phosphorus is removed Biological methods can also eliminate up to 90% of total phosphorus but this method is only suitable for wastewater with low phosphorus concentrations And when there is a change in the chemical composition, high phosphorus concentration, and changes in the temperature of the wastewater, the treatment efficiency is not high Moreover, many of the above methods have long operating times, eliminating ineffective and costly (Wysocka and Sokolowska, 2016) Therefore, electrocoagulation (EC) to remove phosphorus has been used as an alternative process (especially chemical precipitation) Electrochemical (electrolysis + coagulation) combining coagulation, flotation, and electrolysis is a process of destabilizing suspended pollutants or dissolving in water environments using electric current (Fayad, N (n.d.)., 2017) Distinct mechanisms are involved in the removal of the various types of contaminants that exits in water and wastewater which include oxidation, reduction, coagulation, flotation, adsorption, precipitation, and others (Fayad, N (n.d.)., 2017) said that: “As pollutants in raw water and wastewater are mostly colloidal particles, Phosphorus insolubilization (%) Phosphorus insolubilization (%) 100% 80% 60% 40% 20% 0% insoluble Fe / P 100% 80% 60% 40% 20% 0% 2 soluble Figure 3.6 Phosphorus insolubilization (without aeration) 12 insoluble Fe / P 24 soluble Figure 3.7 Phosphorus insolubilization (N2 gas bubbling) 3.1.3 Discussion It has always been known that the process of removing phosphorus by iron electrolysis takes place in the order that iron ions are supplied from the anode and then oxidized by dissolved oxygen in the wastewater and becoming ferric ions These ferric ions combine with phosphate in wastewater to precipitate and settle to the bottom of the tank, as shown in Figure 3.8 Figure 3.8 The existing pathway models 41 However, another way of removing phosphorus by iron electrolysis has been found Based on the results presented above, we can clearly see that the precipitation and deposition process still take place in a different way This pathway is summarized as follows: ferrous ions liberate anodes that can precipitate Fe2(PO4)3 _ iron (II) phosphate and can settle to the bottom of the tank in the anaerobic condition In addition, one hypothesis is also given that the released ferrous ion will precipitate, and this precipitate continues to be oxidized by dissolved oxygen in the wastewater and takes place at the same time as ferrous oxidation into ferric ions Figure 3.9 The new pathway model including ferrous compound coagulation 42 3.2 The effect of humic substance on iron electrolysis 3.2.1 Iron coagulation decrease by humic substance addition Table 3.2 Effluent parameters after electrolysis performed in humic substance addition experiment (n=3) Humic substance addition (ml) Parameter (mg) 20 50 100 150 D-Fe2+ 0.064 ± 0.001 0.07 ±0.003 0.41 ± 0.03 0.66 ± 0.03 0.94 ± 0.03 D-Fe 0.072 ± 0.01 0.08 ± 0.07 0.43 ± 0.003 0.64 ± 0.08 0.93 ± 0.01 D-Fe3+