The objective of research is to build CNST using TVTS to treat pig waste water after microbiological treatment, to minimize environmental pollution. Technology is feasible when applied in practice.
MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY - VU THI NGUYET RESEARCH ON THE APPLICATION OF AQUATIC PLANTS IN THE TREATMENT OF SWINE WASTEWATER Major: Environmental technology Code : 62 52 03 20 SUMMARY OF DOCTORAL THESIS OF ENVIRONMENTAL TECHNIQUE Ha Noi - 2018 The work was completed at the Academy of Science and Technology, Vietnam Academy of Science and Technology Supervisors: Dr Trần Văn Tựa – Environmental technology academy Prof Dr Đặng Đình Kim - Environmental technology academy Counter-argument 1: Counter-argument 2: Counter-argument 3: The dissertation will be defended at the Academic Review Board of the Institute, meeting at the Academy of Science and Technology - Vietnam Academy of Science and Technology at on …’, The dissertation can be reached at: - Library of the Academy of Science and Technology - Vietnam national library INTRODUCTION The necessary of the project In recent years, with the vigorous development of our nation, the economy of rural area has also increased significantly; in which livestock activities have contributed major income for many farmers However, the negative side of this quick development is environmental pollution caused by the waste of livestock activities It is estimated that only 40-50% of total livestock waste is properly treated before discharging to environment, the rest is directly released into ponds, lakes and canals To solve the environmental problem, several technologies have been proposed and conducted to treat livestock waste like physical methods which separate solid and liquid waste, or biological methods based on anaerobic or aerobic condition Among biological methods, biogas technique has been proved to be an appropriate method to treat livestock waste, and it has been widely used nowadays However, some limitations of biogas technique such as high P and N in outlet water that does not meet the permitted standards lead to the necessary to construct an extra-treatment step before discharging into the environment The extra-treatment step aims to reduce the remained P, N and organic matters in effluent to meet standards before discharging One of the potential methods that are suitable for such a goal is eco-technology that uses aquatic plants as a factor to treat the pollutants This method has been reported to have several advantages compared to regular wastewater treatment system Eco-technology is environmentally friendly, low cost, easy to operate, and has a high and stable treatment efficiency Many countries in the world have studied to apply this method Vietnam is a promising country for applying Eco-tech to use aquatic plants in water pollution treatment However, the research and application of this technology in Vietnam remains limited and/or unsystematic, only in small experimental scale and lack of practical research to put the technology into practice Therefore, we conduct the study entitled: "Research on the application of aquatic plants in the treatment of pig waste water" aiming to propose an effective technology for livestock waste treatment, suitable for Vietnam technological conditions, contributing to minimize environmental pollution in residential areas This is a promising strategy to develop sustainable livestock farming along with environmental protection and life quality improvement Study objectives To propose Eco-tech model using aquatic plants to treat pig wastewater after microbial treatment process in order to reduce environmental pollution The technology is feasible and practical Research content Content 1: Overview of the current status of pig wastewater pollution and the treatment technologies; overview of Eco-tech using aquatic plants in wastewater treatment in general, including waste water from pig farms Content 2: Evaluate the tolerance of some selected aquatic plants to COD, NH4+, NO3-, pH, and their ability to treat COD, nitrogen, phosphorus in pig wastewater after microbial treatment Content 3: Evaluate the efficiency of the treatment in different technological types using aquatic plants with different wastewater loads Content 4: Establish and evaluate the treatment efficiency of the aquatic plant system in reducing nitrogen (N), phosphorus (P) and organic matters from pig farm wastewater after the microbial treatment Novel contributions of the study - Selection of suitable aquatic plants for pig wastewater treatment after microbial process based on the efficiency of COD, N, P removal - Selection of the suitable Eco-tech type using aquatic plants to treat swine wastewater - Integration of the selected Eco-tech type into a treatment system of 30 m3 per day- night, effectively additional treating COD, N and P in effluent from pig farms with low cost, simple operation, potential enlargement and adaptation for farm conditions of Vietnam Thesis structure The thesis is presented in 131 pages with 25 tables, 54 figures, and 166 references, including: 3-page introduction, 41-page literature review, 11-page experimental and research methods, 74-page result and discussion, 2-page conclusion and recommendation CONTENTS OF THE THESIS Chapter 1: Literature overview 1.1 The situation of pig farm Livestock farming is the development orientation of the stock-raising sector According to statistic number stated in 2016, there have been total 29 millions pigs in Vietnam, in which the Red River Delta reaches the largest number with 7.4 million pigs (~26%), and this number has been increasing over the years This quick development, however, leads to many problems to our environment caused by the increasing livestock waste 1.2 Survey results of waste from pig farming and treatment technology 1.2.1 Environmental pollution caused by pig farming A total of 20 pig farms were surveyed in five provinces: Hanoi, Vinh Phuc, Hung Yen, Thai Binh and Hoa Binh Water consumption in the farms differs significantly from one to another, varying from 15 to 60 liters/pig/day.night, leading to the amount of waste water is a considerable high number In terms of pollutant composition and level in pig wastewater before biogas treatment; the COD, TN and TP in wastewater were very high reaching to 3587 mg/l, 343 mg/l and 92 mg/l, respectively After biogas treatment, the parameters were reduced to 800 mg/l, 307 mg/l and 62 mg/l, respectively The amount of dissolved oxygen in wastewater before and after biogas treatment was almost zero Coliform index was multiple times higher than the permitted standards Therefore, the pollution caused by piggery farm waste is an urgent situation and needs to be solved 1.2.2 Current status of wastewater treatment technology There are four typical types of technology applied by farms to treat animal wastewater - The wastewater is treated with anaerobic ponds and then through facultative ponds and then discharged into the environment (8.3%) - Livestock wastewater is treated through biogas digester and then discharged into canals (50%) - Livestock wastewater is treated with biogas, followed by biological ponds (25%) - Livestock wastewater is treated by anaerobic stabilization, then treated by anaerobic biological filter or aerotanks, finally through aquatic plant ponds and then discharged (8.3%) The remaining 8.3% of the farms not apply any treatments but directly discharge into the canals, causing serious pollution to the surrounding environment 1.3 Ecological technology in livestock wastewater treatment - Types of aquatic plants in wetlands can be divided into three main groups: semi-submerged aquatic plants, floating aquatic plants and submerged aquatic plants - Types of technology used in Eco-tech for wastewater treatment: surface flow technology, submerged flow technology, and floating aquatic plant system - Pollutant removing mechanism: Nitrogen is removed by mechanisms, nitrification/denitrification, ammonia evaporation and absorption Regarding P, the removal includes: absorption, via bacterial metabolism, adsorption, precipitation and deposition with Ca, Mg ions The treatment process starts with microbial activities to form biofilms on the surface of the aquatic plant shoots and roots; then the microbes digest organic matters in water, releasing nutrient elements like N and P for plant utilization 1.4 Application of aquatic plants in wastewater and pig wastewater treatment - Situation of research in the world: Research and application of Eco-tech with aquatic plants for livestock wastewater treatment in the world has developed for a long time by extensive and intensive researches, not only in small experimental scale, but in large practical scale (from 200 m2 to 15 ha) Common types of technology are surface flow technology and submerged flow technology In Europe, it is popular to combine surface and submerged flows Commonly used aquatic plants are Phragmites australis, Miscanthus sacchariflorus, Vetiveria zizanioides, Cyperus alternifolius, Eichhornia crassipes, Typha latifolia, Schoenoplectus californicus This system is environmentally friendly, low cost, easy to operate, with high efficiency, and stability (COD removing efficiency: 30 - 68.1%, TN: 20 98%, 13 - 95%) - Situation of VN research: Research and application of Eco-tech with aquatic plants for livestock wastewater treatment in Vietnam is still limited, only in small scale from few liters to less than m3, short-term trials, and without a reliable model to put the technology into practice For the reasons above, it is necessary to set up Eco-tech using aquatic plants for pig wastewater treatment to higher levels such as: - Evaluating the tolerance and treatment ability of different aquatic plant species (Eichhornia crassipes, Pistia stratiotes stratiotes, Ipomoea aquatica, Enydra fluctuans, Rorippa nasturtium aquaticum, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius), the selected plants will be used for pilot scale test - Selection of technology types (surface flow technology, submurged flow technology, combined technology), that is suitable for the field treatment model of pig farms in Vietnam - Based on the specific conditions of the farm, construction and evaluation of treatment efficiency of the aquatic plant system will be calculated to effectively reduce N, P and COD from effluent after the microbial treatment at 30 m3/day scale, in Hoa Binh Green Farm, Luong Son, Hoa Binh - Orientate to apply and extend the ecological model in practice Chapter Materials and Methods 2.1 Research subjects Swine wastewater: The wastewater collected from the outlet of microbial treatment process Some aquatic plants have been reported to have ability to treat piggery wastewater: Eichhornia crassipes, Pistia stratiotes stratiotes, Ipomoea aquatica, Enydra fluctuans, Rorippa nasturtium aquaticum, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius 2.2 Research methods 2.2.1 Evaluation of plant tolerance to pollutants and their ability treatment a Evaluation of tolerance to COD, NH4+, NO3-, pH Tolerance of aquatic plants to COD, NH4+, NO3- and pH levels was assessed by plant growth The experimental plants were placed in liters pots containing liters of hydroponic growth medium b Evaluating the plant ability in eliminating some pollutants in the pig wastewater + Batching experiment: The experimental plants were placed in 6-liter pots containing liters of pig wastewater with approx 250 mg/l of COD The experiment was repeated three times with the control (without plants) + Semi-continuous experiment: The experiment was set up as in batching experiment Daily, one liter from the pots is replaced by one liter of new wastewater with the same concentration COD is maintained at about 250 mg/l with glucose supplement c Evaluate the growth of aquatic plants Fresh biomass of plants before and after experiments was measured by Sartorius balance (Germany) For weighing, the plant was removed from the pots, let it drained 2.2.2 Evaluate the capability of pig wastewater treatment of various types of technology - Experiment with floating aquatic plant systems: The experiment was conducted in a tank of the following sizes: High x Long x Width = 60 cm x 200 cm x 50 cm with two compartments: distributing compartment with volume of 10 liters of water; treating compartment with volume of 360 liters The Eichhornia crassipes was deployed on 4/5 of the water surface area Experiment with loading flows: 50 liters/day and 100 liters/day - Experiment with surface flow technology: The experiment was conducted in a tank with size: Height x length x Width = 60 cm x 200 cm x 50 cm with 20 cm soil layer for planting Water level is 20 cm with Phragmites australis, cm with Ipomoea aquatica with water capacity is 180 liters and 45 liters, respectively Phragmites australis density at 15 cm x 20 cm and Ipomoea aquatica at cm x cm Wastewater load was 50 l/day and 100 l/day for Phragmites australis and 25 l/day and 50 l/day for Ipomoea aquatica - Experiment with submerged flow system: The experiment was conducted in a tank with size: Height x length x Width = 60 cm x 200 cm x 50 cm, total water capacity 160 liters Plating substrates included the first layer: crab 4-5 cm (25 cm), second layer: gravel to cm (25 cm), third layer: gravel and small stones ø 0.5 cm (20 cm) Plant density was 15 cm x 20 cm, test loading flow was 25 l/day, 50 l/day and 100 l/day - Experiment with combined flow technology Combination system of Phragmites australis & Eichhornia crassipes: Size of the system: Height x Length x Width = 60 cm x 200 cm x 50 cm comprise two tanks Tank with Eichhornia crassipes (360 liters), tank with Phragmites australis (360 liters including the 20 cm-soil layer and 180 liters of wastewater), the loading flow was 100 l/day Combination system of Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides: The experiment system comprises four compartments: one for Phragmites australis (surface system), one for Cyperus alternifolius and Vetiveria zizanioides (floating plant system), one for Eichhornia crassipes (floating plant system), the last one for Vetiveria zizanioides (submerged flow system) The size of each compartment: Height x Length x Width = 30 cm x 44 cm x 30 cm Test loading flow: 25 liters/day (equivalent to 47.35 liters/m2.day) 2.2.3 Evaluate the efficiency of pig wastewater treatment The ecological system consists of: - Surface flow using Phragmites australis - Floating plant systems include Cyperus alternifolius, Vetiveria zizanioides and Eichhornia crassipes - Submerged flow with Vetiveria zizanioides The ecological model has a total area of 600 m2 divided into compartments, built on flat ground Wastewater flows into compartment 1, through compartment and compartment 3, the outlet at the end of compartment after submerged flow 2.2.4 Analytical methods The pollutants (NH4+, NO3-, T-N, PO4-3, T-P, COD, TSS ) were analyzed according to ISO standard methods by UV-Vis 2450, Shimadzu Japan 2.2.5 Data processing methods Analyzed data were processed by Origin Pro and Excel software 2.2.6 Equipment used in research Equipments used in the study were dosing pump: 2.5 - m3/h, water distillation machine, nitrogen distillation Keldahl, technical and analytical balances, portable device Oxi 330 WTW - Germany, pH 320 WTWW Germany, HACH COD Reactor (United States), TOA (Japan) multiindicator water meter, Japan's Shimadzu UV-2450 spectrometer Chapter Results and discussion 3.1 Tolerance and treatment ability of the aquatic plants 3.1.1 Plant tolerance to the pollutants In order to have a basis for the selection and application of aquatic plants for pig wastewater treatment, it is necessary to assess the tolerance of the aquatic plants Pig farm wastewater is usually characterized by a high organic content while plants in general or aquatic plants in particular are able to tolerate to a certain level Therefore, we conducted an experiment to evaluate the tolerance of selected aquatic plants to COD, NH4+, NO3- and pH in different levels via monitoring plant growth - COD tolerance: COD parameter indicates the level of organic matter pollution of wastewater In pig wastewater, COD is usually very high value Results of the assessment of COD tolerance (Figure 3.1) showed a difference among eight plants, ranking from highest to lowest: Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius > Vetiveria zizanioides > Phragmites australis, Ipomoea aquatica, Pistia stratiotes stratiotes > Rorippa nasturtium aquaticum Figure 3.1 Effect of different COD levels on the growth of aquatic plants Figure 3.2 Effect of different NH4+ levels on the growth of aquatic plants The results indicated that COD was an important factor that influenced on the growth of the plants When the COD level was increased, the plant growth was gradually decreased The higher the COD was, the worse the plants developed The first group including Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius was able to tolerate to 250-750 mg/l COD The second group of Phragmites australis, Vetiveria zizanioides, Pistia stratiotes could tolerate to COD a bit lower, from 250 - 500 mg/l The third group of Ipomoea aquatica and Rorippa nasturtium was able to tolerate at COD < 500 mg/l The results of this study are in consistent with those of Liao X (2000), Jingtao Xu et al (2010) and Tran Van Tua (2011) - NH4+ tolerance: Nitrogen is an important nutrient for plants growth Although NH4+ can be assimilated by plants, NH4+ turns to toxic if the amount is high due to part of ammonia will convert into NH3 Based on the results of the NH4+ tolerance assessment (Figure 3.2), NH4+ tolerance of the eight plants can be ranked as follows: Eichhornia crassipes > Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius > Pistia stratiotes, Rorippa nasturtium aquaticum > Enydra fluctuans >Ipomoea aquatica Eichhornia crassipes, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius can resist NH4+ < 250 mg/l Pistia stratiotes, Rorippa nasturtium aquaticum can tolerate to NH4+ Phragmites australis, Rorippa nasturtium aquaticum, Vetiveria zizanioides > Ipomoea aquatica, Pistia stratiotes Eichhornia crassipes, Enydra fluctuans, Cyperus alternifolius can be resistant to NO3- < 300 mg/l; Phragmites australis, Rorippa nasturtium aquaticum, Vetiveria zizanioides can tolerate to NO3- Rorippa nasturtium aquaticum, Vetiveria zizanioides (figure 3.9) The efficiency of PO43- removal by the plants was ranked in order: Eichhornia crassipes > Pistia stratiotes, Enydra fluctuans, Ipomoea aquatica, Phragmites australiss > Rorippa nasturtium aquaticum, Vetiveria zizanioides, Cyperus alternifolius (Figure 3.10) The optimal remaining time for the aquatic plants to remove pollutants was seven days, which is in accordance with the practical treatment systems Results of other researches using the same aquatic plant system to treat livestock wastewater have also reported a similar observation such as: Sooknah and cs (2004), Tran Van Tua (2007), Ho Bich Lien (2014), Vo Hoang Hoang and cs (2014), Nguyen Hong Son (2016) 3.1.2.2 The efficiency of pollutant removal in semi-continuous experiments The results presented COD and NH4+ removal by crassipes, Enydra fluctuans, Ipomoea aquatica, Pistia nasturtium aquaticum in Fig 3.12 and Fig.3.14, the efficiency of the plants was ranked in order: Eichhornia Phragmites australis>Vetiveria zizanioides, stratiotes, Cyperus alternifolius, Rorippa Figure 3.12: Efficiency of COD Figure 3.14: Efficiency of treatment (%) NH4+treatment (%) The efficiency of TN removal by the plants was ranked in order: Eichhornia crassipes> Ipomoea aquatica, Enydra fluctuans, Phragmites australis, Vetiveria zizanioides, Cyperus alternifolius>Pistia stratiotes, Rorippa nasturtium aquaticum (Figure 3.16) The efficiency of TP removal by the plants was ranked in order: Eichhornia crassipes > Enydra fluctuans, Phragmites australis, Ipomoea aquatica, Vetiveria zizanioides,Cyperus alternifolius > Pistia stratiotes, Rorippa nasturtium aquaticum (Figure 3.17) 12 Figure 3.17: Efficiency of TP Figure 3.16: Efficiency of TN treatment (%) treatment (%) For the all results above, it could be concluded that the COD, TN and TP removal efficiency of different plants was not the same This dissimilar efficiency might be caused from the different tolerance of those plants to the pollutants From the results of tolerant and treatment efficiency study, five plants of tested plants were selected for the further study to assess the ability of pig wastewater treatment after microbial process with different loadings The five plants are Eichhornia crassipes, Ipomoea aquatica, Phragmites australis, Cyperus alternifolius and Vetiveria zizanioides 3.2 Efficiency of pig wastewater treatment after microbial treatment stage by some types of Eco-tech using aquatic plants with different loading wastewater 3.2.1 Floating leaves technology - Eichhornia crassipes The floating leave system effectively remove COD, TN and TP, with COD removal efficiency: 61.5% - 84.9%; TN: 41% - 65.8% and TP: 43.3% - 55.2% (table 3.2) The loads added into the system were 5.1 - 11.6 g COD/m2.day; 4.5 - 10 g TN/m2.day; 0.8 - 1.3 g TP/m2.day The removal amounts from the system were 4.4 - 11.6 g COD/m2.day; 2.9 - 4.1 g TN/m2 day; 0.4 - 0.45 g TP/m2 Table 3.2 Efficiency of treatment system with Eichhornia crassipes Parame ters (mg/l) NO3NH4+ TN PO43- FLOW – 50l/day FLOW – 100l/day input output H% input output H% 41.19 ± 4.67 10.52 ± 2.01 89.79 ± 11.2 13.08 ± 3.24 10.92 ± 3.76 2.24 ± 1.09 30.71 ± 4.15 6.19± 0.63 73.5 78.7 65.8 52.7 47.89 ± 3.90 32.67 ± 4.12 100.3 ± 7.86 9.08 ± 3.92 13.86 ±3.73 14.78 ±3.76 60.53 ±8.04 5.59 ± 0.71 71.1 54.8 41 38.4 13 TP COD TSS pH DO 15.69 ± 1.13 102.5± 8.42 316.7± 61.9 7.26 ± 0.67 3.96 ± 0.39 7.03 ±0.71 15.51 ± 2.00 88.33 ± 29.3 7.37 ± 0.46 2.96 ± 0.29 55.2 84.9 71.2 73.5 78.7 12.52 ± 1.05 115.7± 22.27 338.3± 57.76 7.17 ± 0.28 4.07 ± 0.30 7.10 ± 1.57 44.5± 10.60 133.3± 0.65 7.58 ± 0.34 3.40 ± 0.15 43.3 61.5 60.6 3.2.2 Surface flow technology 3.2.2.1 Surface flow technology using Phragmites australis Surface flow system with Phragmites australis effectively removed COD, TN and TP The removal efficiency of COD was 56.8% - 72.9%; TN: 35% - 53.5%; TP: 33.0% - 42.8% (Table 3.3) The loads added into the system were 5.1 - 11.6 g COD/m2.day; 4.5 - g TN/m2.day and 0.79 - 1.25 g TP/m2.day The removal amounts from the system were 2.5 - 7.8 g COD/m2.day, 2.4 - 3.5 g TN/m2.day, 0.34 - 0.4 g TP/m2.day Table 3.3 Efficiency of treatment system with Phragmites australis Param eter (mg/l) NO3NH4+ TN PO43TP COD TSS pH DO Input FLOW – 50l/ day Output 41.2 ± 4.67 10.5 ± 2.01 89.8 ± 11.17 13.1 ±3.24 15.7 ±2.13 102.5±8.42 316.7±61.9 7.26±0.67 3.96±0.39 14.4 ± 3.73 4.04 ± 1.12 41.7 ± 2.99 7.56 ±0.56 8.97 ±1.69 21.7±3.19 121.7±33.1 7.28±0.58 3.06±0.24 H% 65 61.6 53.5 42.2 42.8 72.9 61.6 FLOW – 100l/day Input Output 47.9 ±3.90 32.7 ±4.12 100.3±7.86 8.58 ±3.26 12.5 ±1.05 115.6±22.2 338.3±57.8 7.17±0.27 4.02±0.34 19.1 ±3.07 16.5 ±3.76 65.2 ±12.8 6.17 ±1.34 8.35 ±2.56 50.0±13.3 163.3±21.6 7.47±0.34 3.05±0.11 H% 60.0 49.4 35.0 28.0 33.0 56.8 51.7 3.2.2.2 Surface flow technology with Ipomoea aquatica The efficiency of COD, TN and TP removal of Ipomoea aquatica system was lower than those with Phragmites australis The COD removal efficiency was 35.5% - 54.3%,; TN: 25.7% - 36.8%; TP: 28.6% - 42.2% (Table 3.4) Table 3.4 Efficiency of treatment system with ipomoea aquatica parameter (mg/l) NO3NH4+ TN FLOW – 25l/day Input Output 47.9 ±3.90 11.3 ±1.88 32.7 ±4.12 15.9 ±2.94 100.3 ±8.26 63.3 ±15.5 H% 76.4 51.5 36.8 FLOW – 50l/day Input Output 41.2 ±3.75 22.1 ±3.47 10.5 ±2.01 5.4 ±1.20 89.8 ±11.17 66.7 ±3.90 H% 46.4 49.2 25.7 14 PO43TP COD TSS pH DO 8.58 ±3.26 12.52 ±1.05 115.8±22.3 338.3±57.8 7.17±0.29 4.07±0.30 5.03 ±0.56 7.24 ±1.84 52.9 ±16.7 151.7 ±29.3 7.83 ±0.22 2.87 ±0.24 41.4 42.2 54.3 55.2 13.1 ±3.24 15.7 ±2.13 102.5 ±8.42 316.7 ±61.9 7.26 ±0.67 3.96 ±0.39 8.1 ±0.44 11.2 ±2.22 66.2 ±6.56 198.3 ±33.1 7.01 ±0.33 2.85 ±0.36 38.1 28.6 35.5 37.4 The loads added into the system were 2.3 - 5.1 g COD/m2.day; 2.5 4.5 g TN/m2.day; 0.31 - 0.75 g TP/m2.day The removal amounts from the system were 1.2 - 1.8 g COD/m2.day; 0.9 - 1.2 g TN/m2.day; 0.13 - 0.22 g TP/m2.day 3.2.3 Surmerged flow technology 3.2.3.1 Surmerged flow technology with Phragmites australis The system with Phragmites australis effectively removed COD, TN and TP, with COD removal efficiency was 30.2% - 79.4%; TN: 27.8% 83.7%; TP: 25.0% - 66.3% The loads added into the system were 2.7 - 12.1 g COD/m2.day; 2.3 - 10.7 g TN/m2.day; 0.3 - 1.2 g TP/m2.day The removal amounts from the system were 2.1 - 3.7 g COD/m2.day; 1.9 - 3.0 g TN/m2.day; 0.18 - 0.3 g TP/m2.day Figure 3.18: Efficiency of surmerged flow technology to treat COD, TN and TP using Phragmites australis 3.2.3.2 Surmerged flow technology with Vetiveria zizanioides The surmerged flow system with Vetiveria zizanioides effectively removed COD, TN and TP, with COD removal efficiency was 38.7% 81.5%; TN: 38.6% - 88.7%; TP: 27.6% - 65.4% The loads added into the system were 2.7 - 12.1 g COD/m2.day; 2.3 - 10.7 g TN/m2.day; 0.28 - 1.2 g TP/m2.day The removal amounts from the system were 2.2 - 4.68 g COD/m2.day; 2.05 - 4.13 g TN/m2.day; 0.18 - 0.33 g TP/m2.day 15 Figure 3.19: Efficiency to treat COD, TN and TP of the system using Vetiveria zizanioides 3.2.4 Combined system of aquatic plants 3.2.4.1 Eichhornia crassipes and Phragmites australis The COD removal efficiency of the system was 69.9%, TN: 76.8%, and TP: 68.8% (Table 3.7) The loads added into the system were 7.8 g COD/m2.day; 5.4 g TN/m2.day; 0.61 g TP/m2.day The removal amounts from the system were 5.4 g COD/m2.day; 4.1 g TN/m2.day; 0.42 g TP/m2.day Table 3.7 Efficiency of Eichhornia crassipes and Phragmites australis system Parameter (mg/l) NO3 NH4 TN PO4 TP COD TSS pH DO Input 79.5 ± 3.54 20.81 ±2.71 107.4 ±3.66 9.84 ±0.75 12.14 ±0.97 155.9±11.13 320.1±93.7 6.98±0.79 3.77±0.49 FLOW - 100 l/ngày ĐR-B1 HB1% ĐR-B2 30.56± 8.5 61.6 12.17± 7.44 11.55 ± 5.1 44.5 7.22 ±4.37 52.45 ±15.9 51.2 24.87 ± 11.9 4.47 ± 1.11 54.6 2.81 ±1.46 5.78 ± 1.76 57.8 3.79 ± 1.71 72.42±11.4 53.5 47.10±9.7 136.6±56.9 57.3 55.86±26 7.61±0.38 7.68±0.18 2.49±0.39 3.49±0.27 HB2 % 60.2 37.5 52.6 37.1 43.4 35 59.1 H% 84.9 65.3 76.8 71.4 68.8 69.8 82.6 Note: ĐR-B1: Output of the Eichhornia crassipes tank; HB1: Treatment efficiency of the Eichhornia crassipes tank; ĐR-B2: Output of the Phragmites australis tank; HB2: Treatment efficiency of the Phragmites australis tank; H: Treatment efficiency of the whole system 3.2.4.2 Combined system of Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides The application of the combined technology allows taking advantage of the each type, improving the efficiency of pollutant removal as well as reducing treatment area 16 The combination system of Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides effectively removed COD, TN and TP The COD removal efficiency was 71.7%; TN: 79.3%; TP: 69.7% The loads added into the system were 9.6 g COD/m2.day; 5.3 g TN/m2.day; 0.64 g TP/m2.day The removal amounts from the system were 6.89 g COD/m2.day, 4.2 g TN/m2.day; 0.45 g TP/m2.day For all the results above, it could be concluded that the combination of the surface system (Phragmites australis), the floating plant system (Cyperus alternifolius, Vetiveria zizanioides and Eichhornia crassipes) and the submerged flow system (Vetiveria zizanioides) showed the most effective treatment in comparison with other regular systems Figure 3.20 Efficiency to treat COD of the system 3.21 Efficiency to treat TN of the system 3.22 Efficiency to treat TP of the system 3.2.5 Comparison of the efficiency of TN, TP and COD treatment by different types of Eco-technology Table 3.8 Comparison of the efficiency of TN, TP and COD treatment of different technology types Technology aquatic plant % Surface flow Floating plant Combined system Ipomoea aquatica Phragmites australis Eichhornia crassipes Eichhornia crassipes Phragmites australis Phragmites australisCyperus TN g/m2.ng Treatment efficiency TP COD % g/m2.ng % g/m2.ng 25.7 1.15 28.6 0.22 35.5 1.8 53.5 2.40 42.8 0.34 72.9 3.7 65.8 2.95 55.2 0.43 84.9 4.4 76.8 4.13 68.8 0.42 69.8 5.4 79.3 4.20 69.7 0.45 71.7 6.9 17 Surmerged flow system alternifoliusWater papyrusVetiveria zizanioides Vetiveria zizanioides Phragmites australis 63.5 3.24 39.6 0.21 64.8 6.8 56.0 2.85 42.6 0.23 62.2 6.6 The results in Table 3.8 indicate that: + Three eco-tech types having the most effective removing TN, TP, and COD are the combination system, floating plant system - Eichhornia crassipes and Vetiveria zizanioides surmerged system + The surface system with Ipomoea aquatica is less effective when applied in the treatment of highly polluted wastewater in TN and TP + With the aim to construct an extra-treatment step for TN, TP and COD in pig wastewater after the microbial treatment in the most economical and effective way, we propose to use combination system including surface technology, floating plant systems and surmerged flow system with Phragmites australis, Cyperus alternifolius, Eichhornia crassipes and Vetiveria zizanioides 3.3 Installation, operation and evaluation of COD, N and P removal efficiency in ecological model (MHST) 3.3.1 Installation System design: The main specifications of ecological model to treat pig wastewater after aerobic treatment are shown in table 3.9 The model occupies a total area of 600 m2 with capacity 30 m3/day built at Hoa Binh Xanh farm, Luong Son district, Hoa Binh province Table 3.9 Specifications of the ecological model TT Parameter COD TN (including N-NH4) Capacity Time of flow Plants Depth of water: - Phragmites australis zone - Floating plants zone - Underground flow zone Standard designs ≤ 450 mg/l - 4500 kg/ha/day ≤ 200 mg/l – 2000 kg/ha/ day ( ≤150 mg/l - 1500 kg/ha/day ) 30 m3/day days Phragmites australis, Eichhornia crassipes , Vetiveria zizanioides, Cyperus alternifolius, 0,35 m 0,60 m 0,60 m 18 Model operation: Seedlings were previously prepared and cultivated in the spring After one month for rooting and stable growth, the system started with gradual increasing load flow: 0.3-0.6-0.9-1.3 m3/h 3.3.2 Evaluation of efficiency 3.3.2.1 COD removal efficiency After months of starting system, MHST was operated to increase the capacity from 0.6 m3/h to 0.9 - 1.3 m3/h to evaluate the treatment efficiency, stability and economic efficiency - 0.6 m3/h load: COD treatment efficiency of MHST in this period was not stable, around 52.1% in average (ranging from 42.7% to 58.5%) The COD load added into the system was about 5.5 g COD/m2.day, and the removal amount was 2.87 g COD/m2.day - 0.9 m3/h load: COD treatment efficiency of MHST in this period was 55.8% in average (ranging from 49.34% to 68.2%) The COD load added into the system was about 6.3 g COD/m2.day, and the removal amount was 3.5 g COD/m2.day - 1.3 m3/h load: COD treatment efficiency of MHST in this period was 59.3% in average (ranging from 53.6% to 65.7%) The COD load added into the system was about 14.7 g COD/m2.day, and the removal amount was 8.7 g COD/m2.day Figure 3.23: MHST COD removal efficiency in Luong Son, Hoa Binh As shown in Figure 3.23, the COD treatment efficiency changed drastically in the initial time, but quickly gained the stability at the load of 1.3m3/h The COD removal amount increased accordingly with the increase of the COD load added into the system The COD removal amount by MHST system was 2.8 - 8.7 g COD/m2.day The similar results were also reported in previous studies conducted by Poach (2004), Kalipci (2011), Vymazal and Kröpfelová (2011), Luu Huy Manh and cs (2014), Nguyen Thanh Loc and cs (2015) 19 3.3.2.2 Nitrogen removal efficiency - Load flow 0.6 m3/h: The TN, NO3- and NH4+ removal efficiencies were 73.8%, 73.8%, and 44.6%, respectively The average TN load added into the system was 4.1 g TN/ m2.day The removal amount was 3.02 g TN/m2.day - Load flow 0.9 m3/h: The average treatment efficiency reached to 67.8%, with NO3- removal efficiency was 74.1%, and NH4+ was 59.2% The system effectively removed both TN and NO3- and NH4+ The average TN load added into the system was 2.4 g TN/ m2.day and the removal amount was 1.62 g TN/m2.day Figure 3.24: TN removal efficiency of MHST in Luong Son, Hoa Binh - Flow load 1.3 m3/h: The TN, NO3- and NH4+ removal efficiencies were 66.2%, 68.5% and 51.8%, respectively The average TN load added into the system was 5.5 g TN/m2.day, and the removal amount was 3.6 g TN/m2.day At this stage, despite the high variation of TN input, the efficiency and stability of the system remained in a high performance This proved that the system in this study well adapted to a high range of load flow and input content In summary, the load added into the system was 2.4-5.5 g TN/m2.day and the removal amount from the system was 1.6 - 3.6 g TN/m2.day The results of this study are in consistent with previous studies carried out by Sohsalam and cs (2008), Zhang (2016) and Le Tuan Anh (2013) The pollutant removal of the combined ecological system demonstrated a higher efficiency than those with only one plant species in a system which was reported by López and cs (2016) and Luu Huy Manh and cs (2014) These positive results were derived from the combination of different aquatic plants, which clearly improved the pollutant removal efficiency of the treatment system The diversity of plants in the system is 20 able to increase plant tolerance to changing environmental conditions as well as stability in biochemical processes (Eviner and Chapin, 2003), limiting the effects of seasonal factors, pests 3.3.2.3 Phosphorus removal efficiency - Load flow 0.6 m3/h: The TP removal efficiency was 50.7% in average (ranging from 47.9% to 54.4%) The average TP load added into the system was 0.8 g TP/m2.day, and the removal amount was 0.41 g TP/m2.day Figure 3.25 TP removal efficiency of MHST in Luong Son, Hoa Binh - Load flow 0.9 m3/h: The TP removal efficiency was 48.8% (ranging from 47.4% to 51.7%) The average TP load added into the system was 1.4 g TP/m2.day and the removal amount was 0.68 g TP/m2.day - Load flow 1.3 m3/h: The TP removal efficiency was 45.3% (ranging from 41.9% to 48.8%) Data from Figure 3.25 indicated that the efficiency in this load flow was relatively stable The average TP load added into the system was 1.9 g TP/m2.day, and the removal amount was 0.86 g TP/m2.day The TP load applied to the system ranged from 0.8 to 1.9 g TP/m2.day and the removal from the system ranged from 0.41 to 0.86 g TP/m2.day The results of this study are in consistent with González (2009), Zhang and cs (2016) Like N, the efficiency of MHST is much higher than that of one-type TVs by Zheng and cs (2016), Valipour and cs (2015) and Pham Khanh Huy (2012) 3.3.2.4 Changes of the hydrological parameters of the ecological model In general, the hydrological parameters of the wastewater were not significant different among the four loading inputs, the output of Phragmites australis, the floating system and the last output of the model except the EC, pH and temperature factors The average value of DO parameter was in between 2.99 ± 1.29 due to the air supply during treatment process 21 The pH values of MHST were significant different between the input and output points (P