Nghiên cứu mô hình kết hợp giữa bãi lọc trồng cây và hồ sinh học để xử lý nước thải khu dân cư ven đô lưu vực sông cầu tt tieng anh

MINISTRY OF TRAINING AND EDUCATION NATIONAL UNIVERSITY OF CIVIL ENGINEERING VI THI MAI HUONG STUDY ON THE COMBINATION MODEL BETWEEN CONSTRUCTED WETLANDS AND STABILISATION PONDS TO TREAT WASTEWATER FROM SUBURBAN RESIDENTIAL AREAS IN CAU RIVER BASIN MAJOR: WATER AND WASTEWATER TECHNOLOGIES CODE: 9520320-2 SUMARY OF PHD THESIS Hanoi, 2019 The PhD thesis has been completed at the National University of Civil Engineering Supervisor: Assoc Prof Dr Tran Duc Ha Dr Nguyen Duc Toan TS Nguyễn Việt Anh Reviewer 1: ……………………………………………………………………… Reviewer 2: ………………………………………………………………………… Reviewer 3: ……….………………………………………………………………… The thesis will be defended at the level of the State Council of Dissertation Assessment’s meeting at National University of Civil Engineering At…… hour…….,day……….month………year 2019 The dissertation is available for reference at the libraries as follows: - National Library of Vietnam - Library of National University of Civil Engineering INTRODUCTION The reasons for choosing the research topic The problem of water polluted in river basins due to wastewater, especially domestic wastewater, which has not been treated or treated is not up to the standard before discharge, is becoming one of the pressing issues in Vietnam Although, the State has approved and implemented the project on environmental protection of large river basins such as Cau river basin (2006), Nhue-Day river basin (2008) and Dong Nai river basin (2007), but the water resource polluted (especially in river sections flowing through urban areas, industrial parks and traditional craft villages ) is still taking place seriously Cau river basin is one of the large river basins in our country It plays an important role in the socioeconomic development of the provinces in the basin The total area of the basin is 6.030 km2 including provinces of Bac Kan, Thai Nguyen, Bac Giang, Bac Ninh, Hai Duong and Vinh Phuc and districts of Hanoi (Me Linh, Dong Anh and Soc Son) The basin has diverse terrain including of high mountainous terrain, midland and plains In recent years, all provinces in the basin have achieved high economic growth rates compared to the national development, especially Bac Ninh, Vinh Phuc, Hai Duong and Hanoi The economic structure develops in the direction of increasing the proportion of industries and services and reducing the proportion of agriculture Along with the rapid economic development, the urbanization process in the provinces of the Cau River Basin is also taking place quickly By 2016, there were 1.8 million people living in urban areas, accounting for 22.22% of the basin population [28] Although infrastructure improves fast, it has not yet met the demand, especially drainage systems and wastewater treatment systems The drainage systems in the urban area of Cau river basin are mostly the general drainage systems built for urban centers, only collecting and treating about 40-70% of total domestic wastewater Currently, in the urban areas of the Cau river basin have been implementing projects on drainage systems and environmental sanitation to upgrade drainage systems and build centralized wastewater treatment plants for urban areas, but still not meeting the demand On the other hand, these projects implement mainly in urban centers, while suburban not pay adequate attention, due to difficult collection Domestic wastewater in these areas run through sewerage systems built by the residents spontaneously, not according to the plan and discharged directly to adjacent water sources such as rivers, streams, ponds, lakes, ditches and low-lying fields near their home Therefore, it becomes one of the main reasons making water in Cau river basin polluted, causing unsanitary environment, loss of beauty, landscapes and negatively affecting community health life Therefore, the organization of wastewater collection and treatment in suburban areas is extremely necessary According to the content of "Planning on drainage systems and wastewater treatment for residential areas and industrial parks in Cau river basin to 2030”, Decentralized drainage systems will be suitable for urban areas and suburban areas in Vietnam in general and Cau river basin in particular Wastewater treatment technologies applied to centralized wastewater treatment systems in urban areas (such as aerotank, oxidation ditches, SBR ) with high construction and operation costs, complicated management and operation will not be suitable to treat wastewater in urban areas and suburban residential areas Therefore, it is necessary to study and propose suitable wastewater treatment technology for these areas Stabilisation ponds and constructed wetlands that are ecological technologies to treat wastewater in natural conditions, low construction and operating costs, simple operation, suitable to available soil conditions of suburban areas will be the appropriate choices On the other hand, if urban areas develop to peri-urban areas, these constructions removed or changed use purposes without spending a lot of investment cost These technologies have been widely applied to treat domestic wastewater and municipal wastewater all over the world in European countries such as Germany, France, England, Poland, Netherlands, Australia, Asian countries such as China, Thailand, India, Indonesia , USA, Canada and African countries In Vietnam, in recent years, stabilisation ponds and constructed wetland are also interested in researching and applying to treat some types of wastewater such as domestic wastewater, municipal wastewater, leachate, livestock wastewater Stabilisation ponds applied for many municipal wastewater treatment plants in Da Nang, Ho Chi Minh City, Da Lat, Buon Ma Thuot, Thanh Hoa Constructed wetlands applied for municipal wastewater treatment in many provinces such as Hoa Binh, Bac Kan, Cao Bang, Tuyen Quang, Thai Binh, Hung Yen, Hai Phong, Thai Nguyen However, when use separately they will have certain disadvantages that limit the applicability Because of the organism composition in the ecosystems of them is relatively homogeneous, combination these technologies to removal wastewater to overcome the disadvantages of each technology and improve removal and the applicability Due to consuming a large area to construct, these technologies are not suitable for wastewater treatment in areas where construction land is lacking, such as urban central areas, but suitable for small and medium scale of suburban residential areas and other scattered drainage objects On the other hand, many surface water bodies (ponds, lakes) in suburban areas can use for wastewater treatment to reduce necessary construction land area Therefore, it is essential to study the applicability of combination of low-cost wastewater treatment technologies in Vietnam, especially for domestic wastewater from dispersed drainage objects such as independent urban areas or suburban residential areas such as suburban residential areas in Cau river basin The research goals - Evaluate domestic wastewater removal of the models combining constructed wetlands with stabilisation ponds - Determining the decomposition coefficients of some typical pollutants in domestic wastewater of constructed wetlands and stabilisation ponds with the natural conditions of Cau river basin - Proposing the technology models combining constructed wetlands with stabilisation ponds to treat domestic wastewater from suburban residential areas of Cau River basin met the standard of Column A of QCVN 14:2008/BTNMT Objects and scopes of research - The objects of research are the models combining constructed wetlands with stabilisation ponds to treat domestic wastewater -Scope of research is domestic wastewater from suburban residential areas in Cau river basin Scientific basis of research Stabilisation ponds and constructed wetlands are ecological technologies; treat wastewater in natural, environment-friendly conditions with low construction and operating costs, simple operation, high removal to pollutants in domestic wastewater such as organic matter, suspended matter, nitrogen, phosphorus and pathogenic microorganisms However, when using these technologies separately in wastewater treatment, there are still certain disadvantages that limit the applicability Therefore, study combination these technologies in a wastewater treatment system will increase removing efficiency and the applicability of them Contents of research - Researching domestic wastewater characteristics from the typical suburban residential areas in Cau river basin are study objects of the experimental model - Research removing pollutants in domestic wastewater from the suburban residential areas in Cau river basin by the models combining constructed wetlands with stabilisation ponds - Assessing the adaptability and selection of plant species grown in constructed wetlands that are suitable to the natural conditions of the Cau River Basin - Determine the organic matter decomposition coefficients of stabilisation ponds used in the experimental model with natural conditions of the study area - Determine the decomposition coefficients to typical pollutants in domestic wastewater of constructed wetlands used in the experimental model with natural conditions of the study area - The study proposes models combined constructed wetlands with stabilisation ponds to treat domestic wastewater that are suitable to natural and socio-economic conditions in the suburban areas in Cau river basin Methodology Based on the objectives, the thesis applied many methods such as overview document, field survey, experimental research and analysis, statistical analysis, compare and consultation of the experts Scientific and practical significances of the research a Scientific significances of the research - Evaluated pollutants removal of domestic wastewater that incur to suburban residential areas in Cau river basin by models combining constructed wetlands with stabilisation ponds - Determined the removal rate coefficients to typical pollutants in stabilisation ponds and constructed wetlands that serve as the basis for designing and operating wastewater treatment systems using the technology combined constructed wetlands with stabilisation ponds - Proposed the technology models combining constructed wetlands with stabilisation ponds to treat domestic wastewater from suburban residential areas of Cau River basin met the standard of Column A of QCVN 14:2008/BTNMT b Practical significances of the research - The research results are important to improve applicability the technology models combining constructed wetlands with stabilisation ponds to treat domestic wastewater from suburban residential areas of Cau River basin met the standard of Column A of QCVN 14:2008/BTNMT - The research results are the reference sources for researchers and managers to select solutions to treat treat domestic wastewater by technology models combining constructed wetlands with stabilisation ponds for suburban residential areas of Cau river basin and for training specialized engineers and masters in university New research contributions - Determined the organic matter decomposition coefficients of facultative and maturation ponds in treating domestic wastewater from suburban residential areas of Cau River basin - Determined the decomposition coefficients to organic matter, compounds of nitrogen, phosphorus of HF and FWS constructed wetlands in treating domestic wastewater from suburban residential areas of Cau River basin - Proposed the technology models combining constructed wetlands with stabilisation ponds to treat domestic wastewater from suburban residential areas of Cau River basin met the standard of Column A of QCVN 14:2008/BTNMT and scope of their application Structure of the thesis The thesis consists of 149 pages of A inserted numbers as follows: Introduction (5 pages); Chapter 1: Overview on domestic wastewater and application of stabilisation ponds and constructed wetlands to treat it (25 pages); Chapter 2: Theoretical basis of stabilisation ponds and constructed wetlands to treat domestic wastewater (30 pages); Chapter 3: Experimental research (21 pages); Chapter 4: Research results and discussion (53 pages); Conclusions, Recommendations (2 pages); List of published papers (1 page); References (12 pages) In addition, the thesis also has a number of non-numbered sections including: The thesis cover (2 pages); Pledge (1 page); Table of contents (4 pages); List of symbols and abbreviations (2 pages); List of tables (2 pages); List of drawings (4 pages) and Appendix (22 pages) CHAPTER 1: OVERVIEW ON DOMESTIC WASTEWATER AND APPLICATION OF STABILISATION PONDS AND CONSTRUCTED WETLANDS TO REMOVE DOMESTIC WASTEWATER 1.1 Overview on domestic wastewater 1.1.1 Characteristics of domestic wastewater Domestic wastewater is water that used for the purposes of eating, living, bathing, cleaning houses, etc from residential areas, public areas, service facilities, etc It contains many pollutants such as biodegradation, suspended matter, N, P nutrients and pathogenic microorganisms If it is not collected and treated meeting standards before discharged into receiving water sources it will become a polluting source to surface water sources, groundwater, causing unsanitary and adversely affecting public health 1.1.2 Collecting and treating domestic wastewater Domestic wastewater collected and treated in two main forms: centralized and decentralized treatment In Vietnam at present, domestic wastewater in urban areas mainly collected and treated in the form of centralized treatment Black water, after preliminary treatment through septic tanks, collected into the sewer collection system along with gray water into the urban drainage system of the city, and then flows to centralized wastewater treatment systems or discharges directly into receiving waters In the past years, the developing urbanization, the population density has increased rapidly while the infrastructure has not been able to meet, especially the drainage system, so the centralized collection and treatment systems have only served for urban areas For areas with low population density that the wastewater collection system is not synchronized, incapable or unable to connect to centralized drainage systems such as suburban residential areas, newly formed residential areas, etc, the most suitable solution is decentralized wastewater treatment 1.1.3 Status of domestic wastewater collected and treated in suburban residential areas in Cau river basin *Urban drainage system in Cau river basin: The process of urbanization has led to the development of urban areas, the rapid increase of urban population and increasingly improved infrastructure, but not met, special urban drainage systems Recently, most of these systems in Cau river basin are general drainage system Rainwater and wastewater are usually collected to a centralized treatment system and discharged into natural canals, canals, ditches and streams, and then to Cau river The main cities in this basin have been implementing projects to upgrade centralized collection and treatment systems However, these projects have implemented only in urban areas and have collected about 40-70% of total domestic wastewater The remaining wastewater did not collected and treated will be naturally permeated and discharged into canals, ditches, streams and Cau River Therefore, it becomes a pollution source of Cau river water * Status of domestic wastewater collected and treated in suburban residential areas in Cau river basin: Due to the impact of urbanization and the results of the "National Target Program on New Rural Construction", the coastal communes have rapid changes in infrastructure and economy, cultural and spiritual life However, domestic wastewater in suburban residential areas and rural areas of Cau river basin has no collection and treatment system met standards before discharging into receiving water sources Environmental pollution is still a pressing issue to residents, especially the drainage systems and wastewater treatment systems 1.2 Overview on research on application of stabilisation ponds to treat domestic wastewater in the world and Vietnam * In the world: Stabilisation ponds have applied to treat wastewater since the beginning of the twentieth century in developed and developing countries The first building in the world built in 1901, in San Antonio, Tex, USA By 1962, there were 1674 stabilisation ponds used in the USA for urban, industrial and agricultural sewage treatment Successful experiences have been published in Australia; New Zealand; Israel, Brazil, South Africa, India and Canada Currently, in the USA, France, Germany and New Zealand, there are 8,000, 2,500, 3,000 and 100 urban wastewater treatment plants using stabilisation ponds respectively * In Vietnam: Until 1985, only some researches on wastewater treatment by stabilisation ponds of Tran Hieu Nhue and Tran Duc Ha proposed urban wastewater treatment technology to protect some water sources in Hanoi and surrounding areas using technologies coagulation - sedimentation and stabilisation ponds Currently, there are 17 urban wastewater treatment systems using stabilisation ponds in wastewater treatment systems built in provinces and cities In addition, the Institute of Water Resources Research of Vietnam has implemented some models applied stabilisation ponds to treat residential wastewater with quite high removal The model combining anaerobic baffle reactor (ABR) with stabilisation ponds to treat wastewater from rural resident area in Tan Hoa - Quoc Oai - Hanoi in 2003; model combining ABR and facultative ponds with plants in ponds to treat domestic wastewater and slaughterhouse wastewater for residential areas in Lim - Tien Du - Bac Ninh, capacity of 30 m3/day from 2006 to 2007 1.3 Overview on research on application of constructed wetlands to treat domestic wastewater in the world and Vietnam * In the world: Studies using constructed wetlands for wastewater treatment first conducted in Germany in the 1950s, in the US in the 1960s and 1970s and subsequently became popular worldwide The first constructed wetland type was free water surface (FWS) systems In Europe, sub-surface flow (SSF) systems through soil and gravel have used very commonly with more than 500 systems for secondary treatment of domestic wastewater from rural areas with a population of about 4400 people In North America this system is often used as a tertiary treatment for biotechnology from areas with crowded population The first SSF type built is the horizontal flow (HF) developed by Kathe Seidel (1965) in Germany Until the 1990s, HF became widespread throughout Europe HF was introduced to North America and Australia in the late 1980s After that, HF were used commonly through out the world such as Germany: 50,000 systems, North America: 8000; United Kingdom: 1000; Italy: 300; Denmark: 200; Czech Republic: 160; Netherlands, Portugal: 120, Slovenia, France, Estonia, Norway, Switzerland Pollutant removal of HF from empirical data of many countries such as Australia, Brazil, Canada, Czech Republic, Denmark, Germany, India, Mexico, New Zealand, Netherlands, Slovenia , Switzerland, USA and UK show that HF has a high removal for BOD, COD, SS and Coliforms reaching 85, 75, 83 and 92%, respectively, but it has a low removal for nutrient about 41, 42, 48 and 35% with TN, TP, NH4+-N and NO3 N respectively Vertical flow (VF) systems were first introduced by Seidel in 1965 in Germany to oxidize effluent from septic tanks However, VF was not as widely developed as HF because of higher cost for operation and maintenance due to the need to pump sewage to distribute on the surface The main advantage of VF was the improvement oxygen exchange in the filter layer which allows higher nitrification and organic matter treatment than HF The transition from HF to VF occurred in Europe in the 1990s due to the need for nitrification and the role of improving oxygen exchange rates VF is used commonly in Europe and the USA Over 250 VF systems had been installed since 1994 in the Netherlands and Belgium * In Vietnam: According to the research by Nguyen Viet Anh et al (2006) in National University of Civil Engineering with the topic: "Domestic wastewater treatment using VF system in Vietnam conditions” from 8/2004 to 12/2005 showed that: VF using gravel or brick materials to treat waste water after septic tanks, planted aquatic plants such as cyperus, reed, and lucky bamboo , treated wastewater met discharge standards and could reuse This technology is suitable to the Vietnam conditions, especially for the scale of households, household groups, tourist destinations, services, farms and craft villages In 2010, Vietnam Water and Environment Investment Corporation (VIWASEEN) implemented some models combining BASTAF tanks with HF to treat domestic wastewater in many provinces in Vietnam such as Hoa Binh, Hung Yen and Thai Binh The treated wastewater quality met the standards column B of QCVN 14:2008/BTNMT, created landscape and reduced pollution for the locality In the Water and Sanitation Program for Small Towns in Vietnam using the ODA fund of the Government of Finland, Phase I and II (2004-2013), some small scale wastewater treatment systems with capacity from 100 to 500 m3/day had been implemented in provinces: Cao Bang, Ha Giang, Tuyen Quang, Yen Bai, Thai Binh, Hung Yen, Hai Phong and Bac Kan The technology was mainly based on the BASTAF – HF implemented in Cho Ra (Ba Be); Yen Lac (Na Ri) and Cho Moi in Bac Kan province In phase III, the Prime Minister approved the list of the Project: "Water and Sanitation Program for Small Towns in Vietnam Phase III" using the ODA fund of the Finland Government However, due to the difficulty of collecting wastewater and funding to operate, these systems are not effective 1.4 Overview on researches on application of models combining constructed wetlands with stabilisation ponds to treat domestic wastewater in the world and Vietnam * In the world: Constructed wetlands applied to improve the water quality out of stabilisation ponds have been used since the early 1990s, from a simple form such as using floating water plants to grow on the surface of a part of outlet water of ponds Currently, FWS and SSF are more commonly used, highly effective with SS loads in the range of 10-48 kg/ha/day with the vegetative cover is fully maintained, especially in the outlet waters of constructed wetlands HF combined with maturation ponds to treat tertiary treatment in Decentralised Wastewater Treatment Systems (DEWATS) researched and transferred by BORDA organization (Germany) since 1993 in many countries around the world Currently, there are more than 500 DEWATS in such countries as Indonesia, India, Philippines, China, Vietnam and South Africa DEWATS considered an effective solution for dispersed sewage from population clusters, hospitals, hotels, farms, slaughterhouses in developing countries The systems usually apply to treat organic wastewater with scale of less than 1000 m3/day They have high removal, adapt to fluctuations in flow rates They are environmentally friendly, simple operation and low costs However, the systems have some disadvantages such as: the design must be suitable to local conditions; use a lot of construction land; stable ground; unable to treat wastewater containing inorganic pollutants such as metals, chemicals, etc The research on domestic wastewater by technology combining stabilisation ponds and constructed wetlands had implemented for a residential area of 825 people in Vermontville, Michigan, USA The system was built on a hill since 1972 including two stabilisation ponds of 4.4 and fourth FWS of 4.6 ha, with a capacity of 3,785 m3/day (0.1MGD) Wastewater characteristics were shown by parameters, such as: BOD5 = 280 mg/L; TKN = 81 mg/L; NO3 N = 1.3 mg/L; TP = 5.3 mg/L The effluent had average parameters concentration as BOD5 = 3.5 mg/L; TSS = 4.2 mg/L; TP = 0.24 mg/L; NH4+-N = 0.86 mg/L; pH = 6.6-7.2; DO = mg/L (5.4-9.4 mg/L) and Fecal Coliforms number per 100 mL under 1000 * In Vietnam: In 2008, the Department of Natural Resources and Environment of Bac Ninh province, funded by the Ministry of Foreign Affairs of the Republic of Sec and the Netherlands Embassy, implemented the project: "Improve the wastewater treatment system in Dao Xa village", built a domestic wastewater treatment system with capacity of 200 m3/day using constructed wetlands and stabilisation ponds The systems operated on 29/4/2009 However, recently the system is overload and stops working The DEWATS introduced by BORDA in Vietnam since 2004 Now, the DEWATS has applied to treat domestic wastewater, industrial wastewater and hospital wastewater in some localities such as Vinh Phuc, Bac Ninh, Hanoi and Ha Nam The results of wastewater quality testing after treated by DEWATS at Kim Bang General Hospital, Ha Nam showed that Coliforms removal was from 95 to 97% and treated wastewater had concentration BOD5 and COD as and 16 mg/L respectively Center for Environmental Consultancy and Technology - Vietnam Environment Administration had implemented two projects on domestic wastewater treatment using technology combining stabilisation ponds and constructed wetlands in 2011 and 2013 In 11/2011, the first project was "Building a model domestic wastewater treatment system with filter technology for residential and urban areas along Nhue - Day river basin” with 950 m3/day capacity The system consists of sand settling tanks, conditioning tanks, pumping stations, vertical sedimentation tanks, stairs overflow, water collection tanks, constructed wetland and stabilisation pond Currently, because the amount of wastewater collected is very small, the plant only operates perfunctorily The second project was "Building a test system to treat domestic wastewater by anaerobic technology combined with HF system", in Bach Quang Ward, Song Cong, Thai Nguyen, with 750 m3/day capacity It checked in 12/2013 The system consists of manhole, screen, sand settling tank, anaerobic filtration tank, pumping station, distribution tank, stairs overflow, distribution manholes, HF system and stabilisation pond Analysis results of concentration pollutants to input and output wastewater after operation for nearly one year had reached the limit column B of QCVN 14:2008/BTNMT Up to now, the system has remained but due to the small amount of wastewater collected, the operation has interrupted Stabilisation pond stocked with dense fish, reducing the role of treatment Therefore, evaluating the efficiency of the system is difficult In 2017, the Institute of Environmental Science and Technology (IESE), National University of Civil Engineering implemented the system that combining stabilisation ponds with constructed wetlands, at 36,000 m3/day capacity The system had the function of incident control, biomarkers and additional treatment for two wastewater flows, which discharged from the biochemical and industrial wastewater treatment system of Formosa Ha Tinh Company Currently, the system operates with high efficiency and ensures the effluent of Formosa Ha Tinh Company meets standards before discharged into the sea 1.5 General comments chapter (1) Domestic wastewater contains high amounts of easily biodegradable organic substances, pathogenic microorganisms, nitrogen and phosphorus, so it should be collected and treated before being discharged into receiving water sources (2) Domestic wastewater can collect and treat by two main forms: centralized wastewater management system and decentralized wastewater management system Today, in Vietnam, the centralized wastewater management system is only suitable for urban areas with crowed population For suburban areas, newly built residential areas, rural residential areas the decentralized wastewater management system is the most appropriate solution (3).Recently the provinces in Cau river basin have fast socio-economic development In suburban areas, there are not the completely technical systems, especially drainage systems Most of the residents discharge wastewater directly into canals, ditches, ponds, lakes, low-lying fields and surrounding lowlands So it become one of the pollution sources for Cau river basin Therefore, it is necessary to organize the decentralized wastewater management system using technologies with low investment, construction and operation costs are extremely urgent (4) Today, stabilisation ponds and constructed wetlands are technologies to treat wastewater in natural conditions, low cost, suitable for small and medium scale of suburban residential areas today However, when used separately in the wastewater treatment system, they will have certain disadvantages that limit the applicability Research on the possibility of combining these two types of technologies to treat wastewater will bring higher efficiency, increase the applicability of them, and contribute to improve the landscape and environment status in these areas (5) In Vietnam recently, there are few studies on the model combined constructed wetlands and stabilisation ponds to treat domestic wastewater met to limit Column A of QCVN 14: 2008/BTNMT Some researches on models combining constructed wetlands and stabilisation ponds to treat domestic wastewater have shown initial results However, there have not been researched to assess and monitor the the actual effectiveness of the systems, not yet showing the combined technology diagrams, design and operation parameters of stabilisation ponds and constructed wetlands when used in combination in a system for wastewater treatment CHAPTER 2: THEORETICAL BASIS OF WASTE STABILISATION PONDS AND CONSTRUCTED WETLANDS TO TREAT DOMESTIC WASTEWATER 2.1 Theoretical basis to treat domestic wastewater by waste stabilisation ponds *Concepts and classification WSPs: WSPs are natural or artificial water bodies, not large When raw sewage directs into the ponds, there will be the processes to metabolism main pollutants due to bacteria and algae living in ponds These processes are similar to the self-cleaning processes in natural rivers and lakes WSPs usually divide into main types: anaerobic ponds, facultative ponds and maturation ponds WSPs often apply to treat municipal wastewater and domestic wastewater with high effectively to organic matter, N, P, and pathogenic microorganisms * Mechanisms of removing typical pollutants in domestic wastewater by WSPs - Mechanisms of removing easily biodegradable organic substances: When wastewater enters ponds with small flow velocity, the sediments will deposit to the bottom The remaining organic substances will absorb and oxidize by bacteria to create products such as biomass, CO2, nitrate, nitrite The decomposition of organic matter carries out mainly by bacteria and Protozoa Bacteria will create CO2 and water in aerobic conditions; create organic acids in anaerobic conditions CO2, phosphorus and nitrogen compounds are used by algae in photosynthesis In this stage, it will release oxygen to oxidation of organic substances by bacteria The activity of algae creates favorable conditions for the metabolism of bacteria - Mechanisms of nitrogen and phosphorus removal: N-organic compounds mineralize into ammonium in anaerobic ponds or in sludge layers Ammonium nitrification process mainly takes place on the surface of facultative ponds and in maturation ponds This process takes place more strongly in the summer than in the winter There are three mechanisms for ammonium removal: evaporation of ammonia, nitrification by Nitrosomonas and Nitrobacter bacteria, and denitrification and synthesis of N in algae biomass Phosphorus removes due to be absorbed into the algae biomass, respiration and deposition Nutrition processes play an important role in N, P removal in WSPs -Mechanisms of pathogenic microorganisms and helminth eggs removal + Pathogenic microorganism removal: The main factors that influence pathogenic microorganism removal in WSPs are light intensity, temperature, pH and HRT Fecal removal increases in high temperature conditions (pH> 9), long HRT and high intensity of light radiation + Helminth eggs removal: Helminth eggs usually remove by deposition in anaerobic ponds and primary facultative ponds * Factors affecting on the pollutant removal by WSPs: The main factors affecting on the pollutant removal by WSPs include temperature, light intensity, concentration and load of organic matter, nutrient, pH and dissolved oxygen concentration * Dynamic model of decomposing organic matter by WSPs It has found that BOD removal often approximates first-order kinetics; that is, the rate of BOD removal (rate of oxidation of organic matter) at any time is proportional to the quantity of BOD (organic matter) present in the system at that time This expresses in Equation as: dL/dt = -kL (2-6) Where L is the quantity of BOD remaining at time “t”, mg/L and k is first-order rate constant for BOD removal, day-1 k ranges from 0.05 to day-1 At T0C: k = kT = k20 (1,06)T-20 (2-7) k depends on temperature, characteristics of wastewater, nutrient concentration, load of organic matter and other biological factors Therefore, k must be determined experimentally according to local conditions and each type of wastewater 2.2 Theoretical basis to treat domestic wastewater by constructed wetlands * Concept: CWs are technical systems that design and build using natural processes involving plants in wetlands, soils and organisms in a system to treat wastewater * Types of CWs: CWs can classify by many different factors but the two most important ones are the flow regime and the type of plants that grow on CWs classify into two main types: Free Water Surface (FWS) constructed wetland and Subsurface Flow (SSF) constructed wetland There are two types of SSF systems: horizontal flow (HF) and vertical flow (VF) * Mechanisms of removing typical pollutants in domestic wastewater by CWs - Mechanisms of removing easily biodegradable organic substances: In CWs, biodegradation plays the most important role in removing dissolved or colloidal organic matter of wastewater The remaining BOD and sediments removes by sedimentation - Mechanisms of nitrogen removal: Nitrogen compounds in wastewater remove in CWs mainly through three mechanisms: nitrification/denitrification, evaporation of ammonia (NH3) and absorption of plants -Mechanisms of phosphorus removal: In CWs phosphorus compounds in wastewater remove by the following mechanisms: adsorption and precipitation on the surface of the filter material, storage in biomass and accumulation in sediment/soil - Mechanisms of pathogenic microorganism removal: Pathogenic microorganism removed by the following mechanisms: Physical processes such as cohesion, sedimentation, filtration, adsorption; unfavorable environmental conditions for a long time such as pH conditions, temperature, solar radiation, nutrient deficiencies eaten by other organisms; Antagonistic relationship between heterotrophic bacteria and the pathogenic bacteria present in wastewater - The mechanism of removing suspended solids: The settled solids easily remove by gravity sedimentation and filtration Non-settling solids, colloids can remove through filtration (if sand filters are used), sedimentation and biodegradation (due to bacterial growth) and adsorption on other solids (plants, soil, sand, gravel, etc.) due to Van der Waals gravity and Brown motion * Dynamic model of decomposing pollutants by CWs - Dynamic model of Reed et al (1995) Reed et al (1995) considers CWs to be the bioreactors in which microorganisms growing adhesion According to Reed, the treatment process of BOD, NH4+-N, NO3 N, in CWs, follow the first-order kinetics with push flow Reed (1995) separates the formulas for TSS and TP The process of removing pathogenic microorganisms in CWs occurs similar to that in WSPs The processes of BOD, NH4+-N and NO3 N removals in CWs describe according to the formula following: (2-23) C  ln  i   KT t  Ce  KT  K R  RTW TR (2-26) Where Ce = outlet effluent pollutant concentration (mg/l), Ci = influent pollutant concentration (mg/l), KR = rate constant at reference temperature (day-1), KT = Rate constant at temperature TW (day-1), t = hydraulic residence time (day-1), TW = water temperature (oC), TR = reference temperature (oC), θR = temperature coefficient for rate constant * Dynamic model of Kadlec and Knight (1996) Kadlec and Knight (1996) also consider CWs as adhesion bioreactors Kadlec and Knight offered a the first-order model with push flow for all pollutants, including BOD, TSS, TP, TN, N-organic, NH4+-N, NOxN, Faecal Coliform Their model relies on first-order reaction rate constants, independent on temperature So the Kadlec and Knight model may be less sensitive to different climatic conditions (2-31) (2-32) q = Q/As (2-33) Where As is treatment area of CWs (m2), Xe is target effluent concentration (mg/l), Xi is target influent concentration (mg/l), X* is background pollutant concentration (mg/l), k is first order aerial rate constant (m/day), q is hydraulic loading rate (m/ngày), and Q is average flow rate through the constructed wetland (m3/day) Kadlec and Knight (1996) support the use of global parameters that they have determined from analyzing the available data of push flows to update the North American database of other systems Specific parameters should be determined locally before investing in the full-scale system, to ensure the fit of the design Therefore, the expressions (2-31) and (2-32) are included in TCVN 7957: 2008 on guidelines for designing CWs *Factors affecting on pollutant removal of CWs: Pollutant removal of CWs depends heavily on environmental and operational factors However, the main environmental and operational factors affecting the treatment efficiency of CWs are pH, temperature, dissolved oxygen, hydraulic load rate/ hydraulic retention time, pollutant load, water supply regime, recirculation flow and biomass harvest 2.3 General comments chapter (1) WSPs are not large natural or artificial water bodies The processes of removing pollutants in the wastewater by WSPs are mainly due to the activity of bacteria and algae The pollutant removal is highly dependent on natural conditions and operational factors WSPs have many advantages such as low cost, easy to build, high stability and high removing efficiency with organic matter and pathogenic orangnism However, WSPs also have some disadvantages such as low suspended solids removal, consuming a large area to construct and odor generation In WSPs, the kinetics of organic matter decomposition is approximate to first-order reaction kinetics k depends on temperature, wastewater characteristics, nutrient concentration, organic matter loading and other biological factors Therefore, k must be determined experimentally according to local conditions and each type of wastewater (2).CWs are technical systems that combine wetland plants, soil/filter materials and microorangnisms to form a system in natural conditions to treat wastewater The processes of removing pollutants in the CWs thank to the physical, chemical and biological mechanisms taking place in the CWs The pollutant removal is highly dependent on natural conditions and operational factors CWs have many advantages such as low cost, easy to operate, environmentally friendly, high treatment efficiency with organic matter, suspended matter and pathogenic microorangnisms, increasing biodiversity and creating landscapes CWs also have disadvantages such as not high efficiency of nitrogen treatment, consuming a large area to construct, high cost for filtration materials, arising odor and harmful organisms The kinetics of the removing pollutants in the CWs are described according to the model of first-order reaction with plug flow, the reaction rate constant (k) should be determined by local experiments to ensure fit of design 12 HRT HLR Day m /m2/day 26/9/201513/12/2015 L/h 5,09 0,125 Canna generalis Day 13,44 4,24 3,05 3,05 13,33 - 0,15 0,075 0,075 - Canna generalis Cyperus alternifolius 3,5 Canna generalis 3,5 3,64 0,175 Canna generalis 2,61 0,0875 Cyperus alternifolius 2,61 0,0875 Canna generalis 11,43 3,18 0,2 Canna generalis 2,29 0,1 Cyperus alternifolius 2,29 0,1 Canna generalis 10 16,12 - Tree species Q HRT HLR Period 3: 13/12/2015m /m /day 21/2/2016 Tree species Q L/h HRT HLR Day m /m2/day Tree species Q L/h HRT HLR Day m /m2/day Tree species Period 4: 21/2/20163/4/2016 11,52 Period 5: 3/4/201729/5/2016 10,08 4,572 0,05 Cyperus alternifolius 3,05 0,075 Canna generalis 16 - * Operating the pilot models + Phase (period 1): From 7/12/2014 to 29/8/2015, model and model operated through the following steps: step 1: preparing materials; step 2: plant trees; Step 3: Load wastewater into the model; step 4: operating the model, monitoring plants growth and sampling + Phase (periods 2, 3, and 5): From 26/9/2015 to 29/5/2016 - Model is operated through the following steps: Step 1: Adjusting the influent flow rate into the model according to the plan shown in Table 3.5 respectively for periods 2, 3, 4, Step 2: Maintaining the models and monitoring the plants growth and taking samples in the respective periods - Model operated through the following steps:  Phase 2: From 26/12/2015 to 13/12/2016: Step is restarting model The model restarted on the September 26, 2015 First taking all the filter gravel out of the non-tree filtration area (HF1) to wash, dry and rearrange filter material layers in the HF1 These layers include one filter gravel layer of 0.6 m thick below and one sand planting layer 0.15 m thick on the top Pump all the wastewater in the maturation pond and clean it Step is planting Cyperus alternifolius planted in HF1 from 4/10/2015 Cyperus alternifolius cut all the leaves Then they split into clusters of 3-5 trees and planted on HF with a distance of 20 cm between the clusters Step is supplying wastewater to the pilot model Supplying wastewater to HF plants to Cyperus alternifolius (HF1') with the flow rate of liters per hour (q = L/h Then adjusting the influent flow rate to the HF to grown Canna generalis (HF2) with flow rate of liters per hour (q = L/h) Step are maintaining the model, monitoring the plants growth and taking samples  Period 3, and 5: From 13/12/2016 to 29/5/2016: Step 1: Adjust the influent flow rate into the model according to the plan shown in Table 3.5, respectively for periods 3, and 5; Step 2: Maintain the model, monitor the growth of plants and take samples of the respective periods * Sampling and analysis plan Table 3.6 Sampling plan during the experiment periods Content Experiment Frequency of Number of Number of Total period Sampling interval sampling (one sampling cycle samples per cycle samples time per week) Period 8/3/2015 -29/8/2015 12 84 Period 8/11/2015 - 13/12/2015 42 13 Period 27/12/2015 -31/1/2016 42 Period 28/2/2016 - 3/4/2016 42 Period 17/4/2016 - 29/5/2016 42 + Sampling locations: Sampling locations follow as: (1).The influent sample- M1; (2) Effluent sample of facultative pond - M2; (3) Effluent sample of FWS - M3; (4) Effluent sample of HF without plant - HF1 (period 1) or HF with plants - HF1' (periods 2, 3, and 5) n- M4; (5) Effluent sample of HF with Canna generalis (HF2) - M5; (6).Influent sample of maturation pond - M6; (7) Effluent sample of maturation pond - M7 * Analytical parameters: pH, TSS, COD, BOD5, TN, N-NH4+, N-NO3-, PO43-, Coliform, biomass and plant height 3.3.3 Research Methods Research Methods include sampling methods, analytical methods in the laboratory, methods of measuring and controlling the wastewater flow rate, Data processing methods and methods of determining kinetic coefficients CHAPTER 4: RESULTS AND DISCUSSIONS 4.1 Removal of domestic wastewater from Bach Quang ward by the conbined facultative pond and FWS (The model 1) 4.1.1 Wastewater characteristics into the model Table 4.1 The results of analyzing the average concentration of the characteristic parameters of wastewater into model QCVN 14:2008 Periods Average /BTNMT Parameters Unit concentration Column A Period Period Period Period Period 7,1 7,1 7,6 7,1 6,9 5÷9 pH 6,9 ÷ 8,5 ÷ 8,5 ÷7,5 ÷8,9 ÷7,3 ÷7,4 83,45 84,83 83,38 83,27 81,95 30 BOD5 mg/L 83,39 ±13,62 ±22,63 ±6,44 ±8,05 ±5,60 ±8,14 70,21 39,83 48,33 47,33 43,33 50 TSS mg/L 53,21 ±16,49 ±19,29 ±4,40 ±10,17 ±4,93 ±7,71 26,00 34,00 35,33 47,33 36,33 TN(*) mg/L 35,19 ± 8,84 ±2,85 ±4,36 ±3,51 ±9,81 ±7,37 23,53 33,18 34,58 40,55 43,67 NH4+ -N mg/L 33,17 ±10,71 ±8,87 ±5,01 ±3,06 ±7,65 ±14,35 2,51 1,30 1,43 2,25 30 NO3- -N mg/L 2,43 ±0,30 2,07 ±0,70 ±0,88 ±0,27 ±0,16 ±0,33 0,35 1,73 1,33 2,42 3PO4 -P mg/L 2,84 ±0,61 1,51 ±0,98 ±0,31 ±0,31 ±0,05 ±0,62 Coliform (**) (MPN/ 100mL) 92.125 ±8.107 - - - - 92.125 ±8.107 3000 The influent is low pollution; there is not much variation between periods, with a neutral pH ranging from 6.90 to 8.50 The parameters NO3 N, PO43 P are all lower than the limit Column A of QCVN 14:2008/BTNMT Wastewater is mainly polluted by TSS, BOD5, NH4+-N and Coliforms The average value of these parameters exceeds limit Column A of QCVN14: 2008/BTNMT, respectively 1.06; 2.78; 6.63 and 30.71 times 4.1.2 Pollutants removal in facultative pond The pollutants load into the facultative pond and pollutants removal during the experiment periods are summarized in Table 4.2 and Figure 4.1 14 Table 4.2 The average pollutants load into the facultative pond during the experiment periods (kg/ha/day) Periods Ordinal Parameters number Period Period Period Period Period BOD5 53,83±14,60 68,38±5,19 80,67±7,79 93,99±6,33 105,72±10,50 TN 16,77±1,67 27,41±3,51 34,18±3,40 53,43±11,08 46,87±9,51 + NH4 -N 15,17±5,72 26,75±4,04 33,45±2,96 45,77±8,64 56,33±18,51 NO3- -N 1,62±0,57 1,05±0,22 1,39±0,16 2,54±0,38 3,44±0,39 PO43 P 0,23±0,20 1,40±30,77 1,29±0,04 2,73±0,70 3,67±0,78 - pH change in the effluent: The pH in the effluent is in the neutral and slightly alkaline range, ranging from 7.6 to 10.6 - Biodegradable organics removal: The removal of biodegradable organics was average, quite stable between experiment periods and ranged from 43.80% to 68.44% When increased the influent flow rates in the range from to L/h (also reduced HRT from 20.16 to 10.08 day) has negligible impact on biodegradable organics removal of this pond Figure 4.1 The average removal in facultative pond to - TSS removal: The TSS concentration in the characteristic parameters of domestic wastewater influent has high volatility and decreases gradually through periods The mean average concentration of TSS is the highest in period and lowest in period as 22.67 mg/L and 11.50 mg/L respectively The TSS average removal ranges from 45.54% to 75.70%, with the lowest in period and the highest in period When increased the influent flow rates from to L/h and reduced HRT from 20.16 to 10.08 days has negligible impact on the algae growth - Nitrogen removal: The average TN loads in the influent vary from 16.77 to 53.43 kg/ha/day The average TN concentration in the effluent tends to increase gradually in the experiments, ranging from 8.00 to 27.00 mg/L, reaching the highest treatment efficiency in period (69.23%) and the lowest in period (32.11%) The average NH4+-N concentration of effluent from period to period 5, ranges from 5.24 to 20.75 mg/L The average NO3 N concentration of effluent was quite variable, ranging from 2.75 to 5.3 mg/L The average NH4+-N removal ranges from 49.24% to 77.72%, reaching the highest value in period and the lowest value in period This range is lower than the NH4+-N removal in facultative pond can reach up to 90% When increasing the influent flow rates from to L/h and reduced HRT from 20.16 to 10.08 days, the NH4+-N removal reduced not much This demonstrates the stability of facultative pond when changing the influent flow rates - PO43 P removal: The average PO43 P loads in the influent vary from 0.23 to 3.67 kg/ha/day The average PO43 P concentration in the effluent is increasing gradually from period to period 5, ranging from 0.18 to 1.89 mg/L The average PO43 P removal has a fluctuation in the experiments, increases slightly in period and gradually decreases in period 3, and increases in period The highest PO43 P removal is 52.30% in period and the lowest PO43 P removal is 21.68% in period When increasing the influent flow rates in period 2, 3, and and reduced HRT from 20.16 days to 10.08 days, the PO43 P removal reduced - Coliforms removal: The average Coliforms number in the influent and effluent are 9.21 x 104 and 8.5 x 10 MPN/100 mL (4.91 and 3.70 logs respectively) Thus, the average Coliforms removal is 1.03 logs This result fit to the synthesis of Ansa E D O et al (2015) about that in facultative pond to domestic wastewater That is in the range of from to logs 4.1.3 Pollutants removal in FWS The influent pollutants loads and pollutants removal in FWS summarize in Table 4.4, Table 4.5 and Figure 4.2 15 Talble 4.4 The average pollutants loads in the influent into FWS through experiment periods (kg/ha/day) Periods Ordinal Parameters number Period Period Period Period Period BOD5 46,91±24,09 41,11±11,67 39,47±12,68 57,14±2,86 60,80±11,50 TN 8,00±2,71 20,42±5,05 24,50±6,24 47,25±3,03 49,33±4,16 NH4+ -N 5,24±2,00 18,51±6,23 16,72±5,18 36,02±4,91 41,50±6,05 NO3- -N 5,3±1,21 3,44±0,63 4,80±1,01 7,38±1,91 8,07±1,03 0,18±0,16 0,88±0,21 1,33±0,11 3,32±0,45 3,55±0,59 3- PO4 -P Talble 4.5 The average concentration of characteristic parameters in the effluent from FWS through experiment periods Parameters Parameters Periods Period Period Period Period Period pH - 6,7 ÷ 7,8 6,5 ÷ 6,8 6,6 ÷ 6,9 6,5 ÷ 6,7 6,5 ÷ 6,9 BOD5 mg/L 8,43±4,24 10,95±2,88 10,35±3,05 15,49±0,68 15,07±2,57 TSS mg/L 4,5±1,13 1,5±0,55 3,33±1,03 6,67±2,73 5,33±2,58 TN(*) mg/L 1,5±0,58 4,33±1,53 8,67±1,53 14,67±2,31 15,67±0,58 NH4 -N mg/L 0,81±0,24 4,10±1,60 5,79±1,54 12,1±1,57 13,08±2,14 NO3- -N mg/L 1,35±1,09 0,72±0,10 1,13±0,21 1,87±0,28 2,17±0,17 PO43 P mg/L 0,12±0,13 0,56±0,24 0,63±0,06 1,39±0,18 1,36±0,23 MPN/100 mL 1.750± 1.269 + Coliform (**) Note: The number of samples in period is 12 (n = 12) The number of samples in periods 2, 3, and are (n = 6); (*): The number of samples in period is (n = 4) The number of samples in periods 2, 3, 4, are (n = 3); (**): The number of Coliform analysis samples in period is (n = 4) The number of Coliform analysis samples in periods 2, 3, 4, are (n = 0) - pH change in the effluent: pH of the effluent has neutral values and be quite stable during experiments, ranging from 6.50 to 7.80 - Biodegradable organics removal: The average BOD5 loads in the influent range from Figure 4.2 The average removal in FWS for characterisic 46.91 to 106.46 kg/ha/day The average BOD5 parameters of domestic wastewater concentrations in the influent increase gradually from period to period with the corresponding values of 8.43, 10.95, 10.35, 15.49 and 15.07 mg/L Average BOD5 removals decrease from period to period with the corresponding levels of 82.04, 66.72, 60.67, 52.55 and 50.43% Thus, when increased HLR into the FWS and reduced HRT corresponding to the experiments are (0.10, 0.125, 0.15, 0.175, 0.20) m3/m2/day and (6.36, 5.09, 4.24, 3.64, 3.18) days, the BOD5 removals reduce negligibly The BOD5 removals in FWS in periods 2, 3, and decreases compared to the period are 15.32, 21.37, 29.48 and 31.60% respectively - TSS removal: The TSS concentrations in the effluent increase gradually through experiments The average TSS concentrations range from 1.50 to 6.67 mg/L, the lowest in period and the highest in period Average TSS removals from period to period are 80.13, 92.68, 84.50, 42.03 and 60.98% respectively When increasing HLR from 0.125 to 0.15 m3/m2/day, the TSS removals in FWS negligibly impacted on 16 However, when increased HLR from 0.175 to 0.20 m3/m2/day, the TSS removals in FWS reduce significantly - Nitrogen removal: The average loads of TN, NH4+-N and NO3 N in the influent vary in the respective intervals as 8.00-49.33, 5.24 - 41.50 and 5.30 - 8.07 kg/ha/day The average concentrations of TN, NH4+-N and NO3 N in the influent into FWS increase gradually in the experiments, with the corresponding ranges of 1.50 - 15.67, 0.81-13.08 and 1.35-2.17 mg/L The average removals of TN, NH4+-N and NO3 N in FWS decrease from period to period When increased HLR to 0.125 m3/m2/day (simultaneously reduced HRT down to 5.09 days), the TN, NH4+-N and NO3 N removals in FWS is negligibly reduced However, when increasing HLR to 0.15, 0.175 and 0.20 m3/m2/day (simultaneously HRT down to 4.24, 3.64 and 3.18 days, respectively), the TN, NH4+-N and NO3 N removals in FWS has reduced much The average removal of TN, NH4+-N and NO3 N of period and period were 81.25, 84.56, 74.63% and 36.49, 36.97, 46.15% respectively This shows that Nitrogen removal in FWS greatly influenced by HLR and HRT - PO43 P removal: The average PO43 P loads in the influent range from 0.18 to 3.55 kg/ha/day The PO43 P concentrations in the effluent increase gradually from period and period 5, from 0.12 to 1.39 mg/L, the lowest in the period and highest in the period The average PO43 P removals decrease from 33.49% (period 1) to 23.41% (period 5) Thus, when increasing HLR into the FWS in the period 2, 3, and the PO43 P removals decrease negligibly - Coliforms removal: The average Coliforms number in the influent and effluent are quite low, respectively 8,500 and 1,750 MPN/100 mL (equivalent to 3.93 and 3.24 logs) Thus, the average Coliforms removal in FWS is 0.69 logs of Coliforms number in the effluent from the facultative pond 4.1.4 Efficiency of domestic wastewater treatment in the model The effluent from the model is the one from the FWS with the concentration of parameters shown in Table 4.5 and wastewater removal in the model is shown in Figure 4.3 - pH change in the effluent: The effluent from the model has a neutral pH, ranging from 6.5 to 7.8 - Biodegradable organics removal: The average BOD5 concentrations in the effluent from model increase gradually from period to period However, they are still low (