Tóm tắt Luận án Research on the application of aquatic plants in the treatment of swine wastewater

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 MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY --------------------------- The work was completed at the Academy of Science and Technology, Vietnam Academy of Science and Technology Supervisors: 1. Dr. Trần Văn Tựa – Environmental technology academy 2. 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 1 INTRODUCTION 1. 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. 2. 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. 2 3. 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. 4. 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. 5. 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 3 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. 1 - The wastewater is treated with anaerobic ponds and then through facultative ponds and then discharged into the environment (8.3%). 2 - Livestock wastewater is treated through biogas digester and then discharged into canals (50%). 3 - Livestock wastewater is treated with biogas, followed by biological ponds (25%). 4 - 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 do 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 3 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. 4 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 1 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 2. 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, 5 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 4 liters pots containing 3 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 4 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 2 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, 5 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 5 cm x 5 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 6 layer: crab 4-5 cm (25 cm), second layer: gravel 2 to 3 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 1 with Eichhornia crassipes (360 liters), tank 2 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 3 compartments, built on flat ground. Wastewater flows into compartment 1, through compartment 2 and compartment 3, the outlet at the end of compartment 3 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 - 3 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) multi- indicator water meter, Japan's Shimadzu UV-2450 spectrometer. 7 Chapter 3. 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 8 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+ <150 mg/l. Enydra fluctuans and Ipomoea aquatica can resist NH4+ < 100 mg/l, all of which is corresponding to the research of Korner (2001), Liao X (2000) and Piyush Gupta et al., 2012. - Tolerance to NO3-: NO3- is an essential compound for the growth and development of plants. With appropriate levels, NO3- along with PO4-3 promotes the development of plants. Compared with ammonium, nitrate is considered less toxic but does not mean that the plants can tolerate any levels Figure 3.3.Effect of different NO3- levels on the growth of aquatic plants Figure 3.4. The effect of different pH levels on the growth of aquatic plants The results of evaluating the effect of NO3- on the growth of aquatic plants in Figure 3.3 showed that the NO3- tolerance of the experimental aquatic plants was higher than the NH4+. Based on growth data, the tolerant order of the plants to NO3- is descripted as follows: Eichhornia crassipes,