Nghiên cứu xử lý nước rỉ rác bằng phương pháp keo tụ điện hóa kết hợp lọc sinh học

Nội dung tài liệu: Nghiên cứu xử lý nước rỉ rác bằng phương pháp keo tụ điện hóa kết hợp lọc sinh học

1. MINISTRY VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY OF EDUCATION AND TRAINING GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY Le Cao Khai RESEARCH ON THE LEACHATE TREATMENT BY ELECTROCOAGULATION METHOD COMBINED WITH BIOLOGICAL FILTRATION Major: Environmental Engineering Code: 9.52.03.20 SUMMARY OF ENVIRONMENTAL ENGINEERING DOCTORAL THESIS Hanoi - 2019
2. This thesis was done at: - Institute of Environmental Technology, Vietnam Academy of Science and Technology - Graduate University of Science and Technology - Vietnam Academy of Science and Technology. Supervisor 1: Assoc.Prof., Dr. Trinh Van Tuyen Supervisor 2: Dr. Le Thanh Sơn The dissertation will be defended at Graduate University of Science and Technology - Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet street, Hanoi. Time: , , 2019 This thesis could be found at: - National Library of Vietnam - Library of Graduate University of Science and Technology.
3. 1 INTTRODUCTION 1. Rationale of the study: Currently, along with the development of society, people lives are gradually improved and consume demand is increasing, leading to an increasing amount of waste, especially domestic waste (DW). The average annual increase is approximately 12%. The regular increase in domestic waste causes an increasing amount of leachate. Leachate is generated from both landfills and transfer stations containing high polluted levels with Chemical Oxygen Demand (COD) up to 70000 mg/l, Dissolved Solids (DS) up to 50000 mg/l, Total Suspended Solids (TSS) to 2000 mg/l and nitrogen content up to 3000 mg/l, Leachate with badly stink affects to surrounding areas and contaminate the groundwater as well as pollute surface water sources. Therefore, environmental pollution by leachate has always been a serious problem which get special attention in environmental protection. Although, according to regulations, each landfill must have a leachate treatment system, most of the current leachate treatment techniques in our country still reveals many weaknesses neither the quality of treated water often does not meet the effluent standards, especially the COD and nitrogen parameters (VN standards 25: 2009/MONRE column B), nor difficult operation and expensive cost. The reason comes from the leachate characteristics with the complex composition and the continuous change by the landfill operating time. The selection of inappropriate treatment technologies has resulted in non- responding to discharge standards, while the leachate in landfills increases continuously. Hence, it is necessary to find some appropriate technologies which are able to handle all the daily leachate, improve current leachate treatment systems and equip for the new landfills. The option of combining electro-coagulation (EC) with biological filtration (BF) is one of the promising solutions to increase the effectiveness of leachate treatment. Unlike chemical coagulation, a large amount of coagulants must be used, thus consuming a lot of chemicals as well as creating a great amount of generated sludge, the EC process has the ability to remove effectively heavy metals, phosphorus compounds, phenol compounds, hydrocarbons and several pathogenic microorganisms, which are difficult to decompose by biological methods. In addition, this process is also easy to automate and minimize the use of chemicals thus reducing the amount of generated sludge. Meanwhile, the BF process has the high treatment performance of suspended compounds (TSS), total nitrogen (TN) and BOD5. In particular, the BF process on inexpensive organic substrates such as peat, wood bark, and plastic have a higher treatment efficiency than conventional BF processes. The reason is that the porous organic substrates have a large specific surface area which is possible to absorb a large amount of microorganisms, together with other physicochemical processes, leading to very strong nitrate reduction. Combining two above
4. 2 technologies allows optimization of leachate treatment process and post- treatment water can reach VN standards 25: 2009/MONRE column B2. Facing this situation, successful research and application of EC technology combined with bio-filter is essential for leachate treatment. Because of this reason, the topic “Research on the leachate treatment by electrocoagulation method combined with biological filtration” is chosen. 2. Study object: This thesis aims to investigate advance techniques for leachate treatment, especially electrocoagulation, biological filtration, and their combination. Through research, the thesis wishes to achieve the following objectives: 1/ Determine suitable conditions for COD, ammonium, TSS and color treatment in leachate by EC. 2/ Determine suitable conditions for COD, ammonium, TSS and color treatment in leachate after EC treatment by BF. The task of the thesis is to study the EC process in combination with BF process to increase the effectiveness of leachate treatment, ensuring environmental standards VN standards 25: 2009/MONRE column B2. 3. Study content: Leachate treatment by EC 1/ Experiments to study the effect of several parameters namely current density, electrolysis time, pH, electrode distance on COD, ammonium, TSS and color treatment in leachate by iron and aluminum electrodes. Leachate treatment by BF after EC process 2/ Experiments to study the effect of aeration modes and input loads on COD, ammonium, TSS and color treatment in leachate after EC treatment by BF. CHAPTER 1. OVERVIEW 1.1 Leachate 1.1.1. Leachate characteristics and composition Leachate is defined as any type of polluted liquid in the rubbish that permeates through the garbage layers in landfills and entitles suspended solids, dissolved colloids from solid wastes discharged into or outside the landfills. The composition of the leachate varies widely depending on the composition of the landfill waste and the landfill time. The pollutant content in leachate of the new solid waste landfill is much higher than the old solid waste landfill. Because in the old landfills, the content of easily biodegradable organic matter has been mostly decomposed. Meanwhile, the leachate in the new landfills usually has a low pH but very high content of COD, BOD5, nutrients, TDS and heavy metals. In contrast to the new landfills, leachate in long-term landfills often has high pH (due to increased methaneization) and the content of COD, BOD5, nutrients, TDS and heavy metals decreases because most of the metals transfer to precipitate state as pH increases. In particular, leachate in long-term landfills contains many high-
5. 3 molecular compounds with many toxic chemicals that both cause dark color and unpleasant odor, which are difficult to decompose by biological methods. 1.1.2. Impact of leachate on the environment and people Leachate has high concentrations of pollutants such as: COD = 2000 - 70000 mg/l, BOD = 1200 - 27000 mg/l and many other toxics which can permeate through the soil and contaminate the underground water sources as well as surface water system. Bad odor in leachate can pollute the air environment. Therefore, when leachate is discharged into the environment, it will cause severe environmental pollution and affect public health. 1.2. Electrocoagulation overview Mechanism of electrocoagulation process “Electrocoagulation is an electrolysis method to treat contaminated water, using direct current (DC) to corrode anode (usually aluminum or iron) and then release coagulants (usually aluminum or iron ions) into the solution”. When metal electrolysis occurs, the following processes occur: M → Mn+ + ne- These metal cations combine with the OH- ions (present in the water) to form metal hydroxides according to the following reaction equations: n+ - M + nOH → M(OH)n 1.3. Bio-filter overview 1.3.1. Mechanism of bio-filter process BF is a technique that uses biofilms formed on a solid carrier. The carrier may have a fixed position in a reaction device and the fluid flow forms a thin film that flows over the surface of the microbiological membrane in trickling filtration technology; microbiological membranes alternately intermittently contact with the gas and liquid phases through a rotating shaft such as in a biological rotating disc. The carrier has a fixed position in a submerged layer and water containing impurities flows through the material layer in the BF column. 1.3.2. Theoretical basis of nitrogen treatment in wastewater by biological processes Nitrogen treatment in wastewater is usually carried out in two stages. Stage 1 is the process of converting ammonium to nitrate (nitrification). The second stage is the process of nitrate denitrifying to evaporate (de-nitrification). 1.3.3. Combining methods in leachate treatment Wiszniowski et al. (2006) have shown that in order to treat the leachate to meet the effluent standards, several methods are needed to combine to treat effectively the leachate. The primary is a combination of 3 methods: physics, chemistry and biology. There have been many studies showing the effectiveness of a combination of methods in leachate treatment. The following is just a combination of EC and BF in leachate treatment. Currently, there are only 2 studies combining EC with BF in leachate treatment. One is to combine BF first, then magnesium - electrode EC. Other is the combination of aluminum electrodes EC before BF process. Both of these results show the
6. 4 effectiveness of EC and BF combination in leachate treatment. However, further studies with other electrodes are needed to find the optimum conditions for leachate treatment with high efficiency and low operating costs. Therefore, the new direction that the thesis focuses on is study on leachate treatment by the combination of iron electrode EC and BF. The dissertation also compares the effectiveness of leachate treatment by iron electrode EC process with aluminum electrode EC process. Therefore, the study of leachate treatment by EC with BF is the direction chosen in this thesis. CHAPTER 2. STUDY OBJECT, SCOPE AND METHODS Figure 2.1. Diagram of leachate treatment by EC combined with BF 2.1. Study object and scope 2.1.1. Study object The pollutants in leachate (evaluated thoroughly several parameters namely COD, ammonium, TSS, color). Leachate used in the study was taken at the biological lake of the Nam Son solid waste treatment complex - Soc Son - Hanoi and stored at 4oC. 2.1.2. Study scope Study on contaminants treatment in leachate by EC method combined with BF at laboratory scale. The block diagram of the research system for leachate treatment in the laboratory is shown in Figure 2.1. 2.2. Study Methods
7. 5 2.2.2. Experimental method of electrocoagulation. Experiments were conducted to find suitable conditions of current density, electrolysis time, pH, electrode distance for leachate treatment. 2.2.3. Experimental methods of bio-filter The experiments were conducted to find suitable conditions for aeration mode, input load for leachate treatment after EC treatment (assessed through COD, ammonium, nitrate, TSS, color). CHAPTER 3. RESULTS AND DISCUSSIONS 3.1. Study on leachate treatment by electrocoagulation Currently, EC is used to treat wastewater. With leachate having high concentration of COD, BOD, ammonium, TSS and color, EC is a new and effective method. - For COD, TSS and pigments are basically treated according to the electrocoagulation mechanism that flocculants are generated from electrolysis. - For ammonium treated basically by the mechanism of electrochemical, adsorption In order to increase the of EC treatment efficiency, such as current density, electrolysis time, electrode distance, electrode material and pH of leachate need to be investigated and found the optimal condition. 3.1.1. Effect of current density and electrolysis time to COD, ammonium, TSS and color treatment efficiency with iron electrodes. Figure 3.1. Effect of current density and Figure 3.2. Effect of current electrolysis time on COD treatment density and electrolysis time on efficiency ammonium treatment efficiency
8. 6 Figure 3.3. Effect of current density and Figure 3.4. Effect of current electrolysis time on TSS treatment density and electrolysis time on efficiency color treatment efficiency The variation of pH during EC process is shown in Figure 3.5: Figure 3.5. The variation of pH in leachate during EC process by electrolysis time Table 3.1. Impact of electrolysis time on COD, ammonium, TSS and color treatment efficiency. (J= 3,896 mA/cm2) Reaction Treatment efficiency (%) time (mins) COD Ammonium TSS Color 10 42,86 8,75 9,83 27,90 20 58,93 12,29 15,95 46,75 30 69,64 17,50 23,98 54,56 40 73,21 19,36 30,46 59,10 Thoi 60 76,79 23,64 38,61 71,67 80 79,29 24,38 38,97 79,39 Impact of electrolysis time from 10 - 80 míns to pollutants treatment efficiency with J= 3,896 mA/cm2 was shown in Table 3.1. When J = 3,896 mA/cm2, according to Table 3.1 we can choose 60 minutes of electrolysis time for the next studies although the efficiency is not the highest at his time, treatment efficiency does not change much after 60 minutes.
9. 7 From Table 3.2 shows, as the current density increases, the power consumption increases. At current density J = 1,298 mA/cm2 (I = 1A), the electrical energy consumption is 1.05 KWh/m3 leachate. As increasing to J = 5,194 mA/cm2 (I = 4A), the power consumption increases to 24,67 KWh/m3 leachate. At current density J = 3,896 mA/cm2 (I = 3A), power consumption is 12,83 KWh/m3 leachate, when increasing current density to 4,545 and 5,194 mA/cm2, power consumption increases considerably, respectively to 18.08 and 24.67 KWh/m3 leachate. The results from Table 3.2 also show that COD, ammonium, TSS and color performance at current density of J = 3,896 mA/cm2 does not change significantly compared to J = 4,545 and 5,194 mA/cm2. The energy consumed to treat 1 m3 of leachate at J = 5,194 mA/cm2 is almost double that of J = 3,896 mA/cm2. Therefore, selecting the current density of J = 3,896 mA/cm2 is energy-efficient while the COD, ammonium, TSS and color performance are not much lower than J = 4,545 and 5,194 mA/cm2. Table 3.2 show that if the current density is smaller than 3,896 mA/cm2, neither the power consumption is low nor COD, ammonium, TSS and color treatment efficiencies are small. Therefore, current density of J = 3,896 mA/cm2 is applied to the next studies. Table 3.2. Power consumption and COD, ammonium, TSS and color treatment efficiencies. COD Ammonium TSS Color Current Current Power Potential treatment treatment treatment treatment intensity density consumption (V) efficiency efficiency efficiency efficiency (A) (mA/cm2) (KWh/m3) (%) (%) (%) (%) 1,0 1,298 1,9 1,05 53,33 14,03 6,85 42,2 2,0 2,597 4,4 4,89 62,50 15,03 20,79 56,5 2,5 3,246 5,5 7,64 69,64 18,32 26,57 59,6 3,0 3,896 7,7 12,83 76,79 23,64 38,61 71,67 3,5 4,545 9,3 18,08 78,71 24,32 39,04 74,27 4,0 5,194 11,1 24,67 80,36 24,99 40,16 74,91 Combining the treatment efficiencies in Table 3.1 and the power consumption in Table 3.2, it is convincing to choose electrolysis time of 60 minutes for further studies. 3.1.2. Effects of initial pH in leachate on COD, ammonium, TSS and color treatment efficiencies with iron electrodes. The pH value is one of the main factors affecting the treatment efficiency of the EC process. The results also show that, in neutral environment (pH = 7-8), COD, ammonium, TSS and color removal efficiency are highest (specifically in Table 3.3).
10. 8 Figure 3.6. Effect of initial pH on Figure 3.7. Effect of initial pH on COD treatment efficiency ammonium treatment efficiency Figure 3.8. Effect of initial pH on Figure 3.9. Effect of initial pH on TSS treatment efficiency color treatment efficiency Table 3.3. The COD, ammonium, TSS and color treatment efficiencies at different pH (J = 3,896 mA/cm2, 60 mins electrolysis, electrodes distance of 1 cm) Treatment efficiency (%) pH COD Ammonium TSS Color 5 50,00 14,33 16,65 24,11 6 69,62 22,02 18,95 40,99 7 73,91 22,63 30,55 67,1 8 72,00 24,88 39,93 72,2 9 62,90 19,22 19,26 50,71 Form Table 3.3, it can be seen that the treatment efficiency reaches the highest at pH from 7 to 8. Studying the effect of the input pH also shows that when pH is larger than 8, COD, ammonium, TSS and color treatment efficiencies decrease. The more the electrolysis time increases, the more the pH increases (according to Figure 3.5), resulting in a reduction in treatment efficiency. This is also the basis to explain when the electrolysis time is greater than 60 minutes, the
11. 9 treatment efficiency increases lightly or no increase. On the other hand, the input pH of Nam Son landfill leachate is around 8, then the input pH (about 7-8) is chosen for the further studies to save pH adjustment chemicals and cost. 3.1.3. Effects of iron electrodes distance to COD, ammonium, TSS and color treatment efficiencies Figure 3.10. Effect of electrodes Figure 3.11. Effect of electrodes distance distance on COD treatment efficiency on ammonium treatment efficiency Figure 3.12. Effect of electrodes Figure 3.13. Effect of electrodes distance distance on TSS treatment efficiency on color treatment efficiency Table 3.4. COD, ammonium, TSS and color treatment efficiencies at different electrodes distances (J = 3,896 mA/cm2, electrolysis time of 60 mins) Electrodes Treatment efficiency (%) distance (cm) COD Ammonium TSS Color 1 76,79 23,64 38,61 71,67 3 63,71 20,38 27,21 64,2 5 50,00 14,85 21,1 44,1 7 45,65 10,54 8,02 28,5 Table 3.4 shows that at the electrode distance of 1 cm, the highest treatment efficiency is achieved with COD, ammonium, TSS and color efficiency respectively: 76.79; 23.64; 38.61 and 71.67%. When the distance between the plates increases, the pollutants removal performance decreases. In this study, it is not possible to reduce the electrode distance to less than 1 cm because the characteristics of Nam Son landfill leachate has high TSS content
12. 10 causing instability in the electrolysis process. Therefore, the electrode gap of 1 cm is selected to apply for the study. The results of the study showed that in the current density of J = 3,896 mA/ cm2, the input pH from 7 - 8 and the electrode gap of 1 cm are an optimum condition for EC process. 3.1.4. Comparison the COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes. Comparison the COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes at different electrolysis times. Figure 3.14. Effect of electrolysis time Figure 3.15. Effect of electrolysis time on COD treatment efficiency by iron on ammonium treatment efficiency by electrodes in comparison with iron electrodes in comparison with aluminum electrodes aluminum electrodes Figure 3.16. Effect of electrolysis time Figure 3.17. Effect of electrolysis time on TSS treatment efficiency by iron on color treatment efficiency by iron electrodes in comparison with electrodes in comparison with aluminum electrodes aluminum electrodes Electrode material is one of the parameters that directly affects the electrolysis reactions taking place inside the solution. In each EC reaction, dissolved anodes and flocculants play an important role to assess the method effectiveness.
13. 11 The effect of electrolysis time on COD, ammonium, TSS and color treatment efficiencies of iron and aluminum electrodes are shown in Table 3.5. Table 3.5 shows that the COD, TSS and color treatment efficiencies of iron electrodes are much higher than aluminum electrodes at all electrolysis time. Whereas the ammonium removal efficiency of iron and aluminum electrodes depends on the electrolysis time. Thus, it is clearly to choose the iron electrodes for research on leachate treatment by EC. Table 3.5. COD, ammonium, TSS and color treatment efficiencies with iron and aluminum electrodes at different electrolysis time. (J = 3,896 mA/cm2, electrodes distance of 1 cm) Treaatment efficiency (%) Electrolysis COD Amoni TSS Color time (mins) Fe Al Fe Al Fe Al Fe Al 10 42,86 6,90 6,64 5,46 9,83 6,71 27,90 19,90 20 58,93 17,24 11,71 8,19 15,95 9,12 46,75 32,91 30 69,64 22,41 14,06 11,34 23,98 14,2 54,56 41,24 40 73,21 37,93 17,770 18,48 30,46 23,4 59,10 45,85 60 76,79 44,83 23,64 26,46 38,61 27,1 71,67 58,98 80 79,29 44,83 24,79 30,24 38,97 29,1 79,39 66,64 Comparison the COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes at different input pH of leachate. Figure 3.18. Effect of pH on COD Figure 3.19. Effect of pH on treatment efficiency with iron and ammonium treatment efficiency with aluminum electrodes iron and aluminum electrodes
14. 12 Figure 3.20. Effect of pH on TSS Figure 3.21. Effect of pH on color treatment efficiency with iron and treatment efficiency with iron and aluminum electrodes aluminum electrodes Table 3.6. COD, ammonium, TSS and color treatment efficiencies with iron and aluminum electrodes at different input pH. (electrolysis time of 60 mins, electrodes distance of 1 cm) Treatment efficiency (%) pH COD Amoni TSS Color Fe Al Fe Al Fe Al Fe Al 5 50,00 18.72 14.33 15.87 16.65 13.8 24.11 22.5 6 69.62 35.9 22.02 23.57 18.95 15.24 40.99 35.7 7 73.92 44.83 22.63 25,56 30.55 22.97 67.04 60.2 8 72,00 43.58 24.88 26.46 39.93 35.83 72.19 65.13 9 62.90 30.76 19.22 22.48 19.26 13.05 50.70 45.63 10 43.75 14.2 11.23 15.76 15.74 11.38 34.58 30.32 Table 3.6 shows that the COD, TSS and color treatment performance using iron electrode treatment efficiency are much higher than the aluminum electrode at all pH values. Meanwhile, the ammonium removal efficiency of aluminum electrode is higher than iron electrode. In acidic (pH 8) environments, COD, ammonium, TSS and color treatment efficiency of both aluminum and iron electrodes are low. This phenomenon was explained by Park et al. (2002): each type of metal ion in solution can create different coagulants leading to different performance of pollutant treatment. For example, the high alkali conditions in aluminum hydroxide and iron hydroxide - - solutions exist in the form of Al(OH)4 and Fe(OH)4 respectively. These hydroxides have poor flocculation activity, then, usually (except for some polyaluminum products) the coagulant process is difficult to perform in an acidic environment (Fe: pH = 4 - 5 and Al: pH = 5 - 6). This result is the basis for selecting the input pH value of the leachate and the appropriate electrode type. The initial pH 7 - 8 is chosen for both types of
15. 13 electrodes because this is the pH range for the highest COD, ammonium, TSS and color performance. Comparison the COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes at different electrodes distances Figure 3.22. Effect of electrodes Figure 3.23. Effect of electrodes distance on COD treatment efficiency distance on ammonium treatment in comparison iron with aluminum efficiency in comparison iron with electrodes aluminum electrodes Figure 3.24. Effect of electrodes Figure 3.25. Effect of electrodes distance on TSS treatment efficiency distance on color treatment efficiency in comparison iron with aluminum in comparison iron with aluminum electrodes electrodes Table 3.7 shows that the COD, TSS and color treatment performance using iron electrodes are much higher than aluminum electrodes at all electrode distances. Meanwhile, the ammonium removal efficiency of aluminum electrode is higher than iron electrode but not much. This result is the basis for selecting suitable electrode distances and electrode types. The results from the research on leachate treatment performance between aluminum and iron electrodes in the same conditions showed that iron electrodes are proved to be superior in COD, TSS and color removal
16. 14 performance. Although the ammonium removal efficiency of the aluminum electrode is higher than the iron electrode, it is not considerable. With the same amount of removed pollutants, the consumed energy using iron electrodes can be calculated to be smaller than that of aluminum electrode. The cost of the electrodes is also an issue, as the iron electrodes is lower than the aluminum electrodes. Therefore, iron electrodes were chosen for this study. Comparing the results of study on COD, ammonium, TSS and color treatment performance in leachate at appropriate conditions with previous studies is shown in Table 3.8: Comparing the results of the thesis with other studies shows that some leachate indicators in this study have higher treatment efficiency and lower energy consumption. Table 3.7. COD, ammonium, TSS and color treatment efficiencies between iron and aluminum electrodes in different electrodes distances (J = 3,896 mA/cm2, electrolysis time of 60 mins) Electrodes Treatment efficiency (%) distance COD Amoni TSS Color (cm) Fe Al Fe Al Fe Al Fe Al 1 76,79 44,83 23,64 26,46 38,61 27,1 71,67 67,32 3 63,71 30,00 20,38 20,80 27,21 25,71 64,25 55,46 5 50,00 26,70 14,85 15,60 21,10 18,93 44,42 37,29 7 45,65 22,60 10,54 11,24 8,02 6,95 28,44 20,87 Some comments on the leachate treatment by EC The study results show that COD, TSS and color treatment efficiencies by EC process using aluminum electrodes are lower than iron electrodes whereas the ammonium removal performance of aluminum electrodes is higher than iron electrodes after more than 40 minutes reaction. This is the basic for selecting electrode types in further application. Most of the previous studies have demonstrated that the COD removal efficiency of iron electrodes is higher than that of aluminum electrodes, but Ilhan et al. (2008) showed the opposite results of COD removal efficiency of electrodes. Aluminum is higher than iron electrode. The research results also show that the EC process is effective for COD and color treatment because COD and color can be basically removed by the electrolytic flocculation processes combined with the electrolytic processes such as oxidation, adsorption. . The EC process is ineffective in the treatment of ammonium because, unlike the COD, TSS and color processes, ammonium is treated primarily by electrolysis and chemical processes. When studying the EC process in the leachate treatment, the suitable conditions for the treatment are found: iron electrodes, J = 3,896 mA/cm2, initial pH = 7 - 8, the electrode distance of 1 cm, electrolysis time of 60 minutes.
17. 15 Study results show that the EC process is a promising method for to treat leachate. However, if only EC process is used, some parameters of the effluent discharges have not met the discharge requirements. Further processing is required. In this thesis, after EC process, treated water continues to be studied by BF treatment. After the EC process, some of the pollutants remaining in leachate were: COD 75%, TSS > 60% and color < 30% compared to the original. Thus, ammonium and TSS are subject to treatment in the next biological process. Table 3.8. Comparison the COD, ammonium, TSS and color treatment efficiencies in different studies at selected conditions Treatment efficiency (%) Enery/m3 Study leachate COD Amonium TSS Color (KWh) Thesis 71 - 77 24 - 25 38 - 40 71 - 72 12,83 Bouhezila F. et al (2011) 68 15 (TN) - 28 19 Ilhan F. et al (2008) 59 14 - - 12,5 – 19,6 Li X. et al (2011) 49,8 38,6 - - - Catherine R. et al (2014) - - - 80* - Top S. et al (2011) 45 - - 60 - Orkun M. O.et al. (2012) 65,85 - - - - Shivayogimath C.B. et al. 53,3 - - 65 - (2014) 1.2 Study on leachate treatment by bio-filter method Table 3.9. Some characteristics of NRR after EC process used for input of BF process No. Parameters Unit After EC 1 pH - 8,7 – 9,1 2 COD mg/l 717 - 870 3 BOD5 mg/l 312 - 337 + 4 NH4 -N mg/l 410 - 484 - 5 NO3 -N mg/l < 1 6 TSS mg/l 471 - 578 7 Color Pt-Co 316 - 402 In order to treat thoroughly COD, ammonium, TSS and color, the thesis has combined two methods namely EC method and followed by BF system. Similar to the EC method, the biological treatment need to optimize the treatment conditions such as aerobic and anerobic treatment processes, aeration rates, dissolved oxygen, input loads to find the optimal conditions. 3.2.1. Effect of aeration modes on COD, ammonium, TSS and color treatment efficiencies by bio-filter process
18. 16 To evaluate the effect of aeration modes on COD, ammonium, nitrate, TSS and color performance, a series of experiments is performed with an inlet flow of 3 liters/day in 4 other aeration modes from 1 to 4. The volume of this bio-filter is always fixed. 3.2.1.1. Effect of aeration modes on COD treatment efficiency Mode 1: Mode 2: Mode 3: Mode 4: 60/60 45/75 30/90 15/105 Figure 3.26. Effect of aeration modes on COD treatment efficiency 3.2.1.2. Effect of aeration modes on ammonium treatment efficiency Mode 1: Mode 2: Mode 3: Mode 4: 60/60 45/75 30/90 15/105 Figure 3.27. Effect of aeration modes on ammonium treatment efficiency 3.2.1.3. Effect of aeration modes on nitrate treatment efficiency
19. 17 Mode 3: Mode 4: 30/90 15/105 Mode 1: 60/60 Mode 2: 45/75 Figure 3.28. Effect of aeration modes on nitrate treatment efficiency 3.2.1.4. Effect of aeration modes on TSS treatment efficiency Mode 1: Mode 2: Mode 3: Mode 4: 60/60 45/75 30/90 15/105 Figure 3.29. Effect of aeration modes on TSS treatment efficiency 3.2.1.5. Effect of aeration modes on color treatment efficiency
20. 18 Mode 1: Mode 4: 30/90 15/105 Mode 2: Mode 3: 45/75 30/90 Figure 3.30. Effect of aeration modes on color treatment efficiency Table 3.10 shows that, when reducing aeration time, COD, ammonium and color treatment efficiencies decrease, however, TSS treatment efficiency increases. Thus, mode 1 aeration/non-aeration time = 60/60 minutes has the highest treatment efficiency for COD, ammonium and color, but the output nitrate concentration is too large compared to the prescribed standards. Whereas at mode 4 aeration/non-aeration time = 15/105 minutes, the nitrate concentration is around 44 mg/l. If aeration time continues to reduce in one cycle, it is a rule that the system's ability to handle nitrogen is better but the COD, ammonium and color removal performance are low. The operating cost of anaerobic - aerobic BF system mostly comes from the cost of aeration. Therefore, the shorter aeration time in a cycle, the lower energy cost. In terms of treatment efficiency in modes (especially with nitrogen treatment) and aeration cost, aeration/non-aeration mode = 15/105 minutes is chosen for further studies. Table 3.10. COD, ammonium, nitrate, TSS and color treatment efficiencies under different aeration modes Treatment efficiency Aeration/non- aeration mode Outlet Amonium (mins) COD (%) nitrate TSS (%) Color (%) (%) (mg/l) 90,64 ± 371,87 ± 84,36 ± 55,13 ± Mode 1 (60/60) 99,88 ± 0,04 0,88 9,13 0,66 1,81 84,91 ± 254,5 ± 87,39 ± 46,03 ± Mode 2 (45/75) 99,62 ± 0,03 1,17 14,70 0,52 1,14 79,54 ± 160,32 ± 89,20 ± 39,09 ± Mode 3 (30/90) 99,52 ± 0,03 1,00 8,44 0,57 1,61 77,45 ± 91,07 ± 34,75 ± Mode 4 (15/105) 99,21 ± 0,03 43,64 ± 1,16 1,31 0,52 1,30
21. 19 With the aeration/non-aeration mode = 15/105 minutes, if the total nitrogen is the sum of ammonium, nitrate and nitrite, the total output nitrogen reaches VN standards 25: 2009/MONRE column B2. 3.2.2. Effect of input loads on COD, ammonium, nitrate, TSS and color treatment efficiencies by biological filtration process The amount of pollutants load has a great influence on the performance of the BF method. Wijeyekoon et al. (2004) proved that pollutants load also affects biomass growth. Specifically, the internal microorganism structure is affected by the increase in load, increasing the concentration of internal sludge, consequently, the porosity of the microbiological membrane is reduced. Therefore, the input load is an important factor to assess the processing threshold of the BF system. A series of experiments investigating the effect of the input loads on COD, ammonium, nitrate, TSS and color removal performance are carried out according to modes 4-8, with the following conditions: aeration/non-aeration: 15/105 minutes gas; the pH of the leachate solution after EC treatment is about 8.7 - 9.1; the inlet flow varies from 3 to 7 liters/day, DO as aeration is 6-7 mg/l, room temperature (25 - 32oC). 3.2.2.1. Effect of input loads on COD treatment efficiency. Mode Mode Mode Mode Mode 4: 3 lít 5: 4 lít 6: 5 lít 7: 6 lít 8: 7 lít Figure 3.31. Effect of input loads on COD treatment efficiency (aeration/non-aeration mode: 15/105 mins) 3.2.2.2. Effect of input loads on ammonium treatment efficiency
22. 20 Mode Mode Mode Mode Mode 4: 3 lít 5: 4 lít 6: 5 lít 7: 6 lít 8: 7 lít Figure 3.32. Effect of input loads on ammonium treatment efficiency (aeration/ non-aeration mode: 15/105 mins) 3.2.2.3. Effect of input loads on nitrate treatment efficiency Mode Mode Mode Mode Mode 4: 3 lít 5: 4 lít 6: 5 lít 7: 6 lít 8: 7 lít Figure 3.33. Effect of input loads on nitrate treatment efficiency (aeration/ non-aeration mode: 15/105 mins) 3.2.2.4. Effect of input loads on TSS treatment efficiency
23. 21 Mode Mode Mode Mode Mode 4: 3 lít 5: 4 lít 6: 5 lít 7: 6 lít 8: 7 lít Figure 3.34. Effect of input loads on TSS treatment efficiency (aeration/ non-aeration mode: 15/105 mins) 3.2.2.5. Effect of input loads on color treatment efficiency Mode 5: Mode 4: Mode 6: 4 lít 3 lít 5 lít Mode 7: Mode 8: 6 lít 7 lít Figure 3.35. Effect of the input loads on the color treatment efficiency (aeration/ non-aeration mode: 15/105 mins) Table 3.11 shows that, when the input load increases, the treatment efficiencies of COD, ammonium, TSS, color all decrease. Mode 4 shows the lowest output nitrate concentration, when the load increase, the total concentration of output nitrogen increases to near the allowed level. If the load continues to increase, the nitrogen treatment capacity of the system does not reach VN standards 25: 2009/MONRE column B2 but the COD and ammonium performance is still reached. Therefore, it is no longer possible to increase the load. Therefore, the conditions being suitable for the further study are mode 4: 15 minutes aeration/105 minutes non-aeration and an input ammonium load does not exceed 0.16 kg/m3/day.
24. 22 Table 3.11. COD, ammonium, nitrate, TSS and color treatment efficiencies under different loading modes COD Amoni Nitrate TSS Color Input Amonium volume Load Treatment Load Inlet Load Treatment Treatment treatment Outlet (l/day) kg/m3 efficiency kg/m3 (mg/ kg/m3 efficiency efficiency efficiency (mg/l) day (%) ngày ngày (%) (%) (%) l) CĐ 4 0,120 ± 77,46 ± 0,066 ± 99,21 ± 43,64 0,077 ± 91,07 ± 34,75 ± (3) 0,004 1,22 0,0013 0,03 ± 1,16 0,0017 0,52 1,30 CĐ 5 0,162 ± 76,32 ± 0,089 ± 99,12 ± 44,84 0,103 ± 88,46 ± 31,00 ± (4) 0,004 0,59 0,0013 0,02 ± 0,74 0,0023 0,36 0,58 CĐ 6 0,202 ± 75,51 ± 0,112 ± 99,01 ± 46,92 0,129 ± 86,46 ± 28,32 ± 90 (BOD5) 94 - - 97 Amonium 24 - 25 98,88 ± 0.01 94 - - > 99 TSS 38 - 40 83,34 ± 0,53 - - - - Color 71 - 72 16,7 ± 0,75 85 60 ± 13 - Energy/m3 12,83 - - - 1,23 US$ - NRR (KWh) Figure 3.36 shows the total treatment efficiencies of COD, ammonium, TSS and color are about 91.7; 97.77; 87.65 and 75.89% respectively. Thus, COD, ammonium, TSS and color treatment efficiencies of bio-filter system are relatively high and there is a close combination of treatment efficiency between EC and BF process.
25. 23 Figure 3.36. COD, ammonium, TSS, color treatment efficiencies in leachate by EC combined with BF (EC: J = 3,896 mA/cm2; time = 60 mins; electrodes distance = 1 cm. BF: A/N-A= 15/105 mins; DO aeration = 6 -7 mg/l; the load = 7 l/d) Output parameters after EC and BF process under selection conditions are shown in table 3.13. Table 3.13. Output parameters after EC and BF process under selected condition After BF (A/N-A: 15/105 Parameters Unit Before EC After EC mins; input load: 7l/d) COD mg/l 2930 - 3065 717 - 870 182 - 245 BOD5 mg/l 958 - 1106 312 - 337 15 - 32 + NH4 -N mg/l 556 - 635 410 - 484 4,8 – 5,2 - NO3 -N mg/l 1,3 – 2,1 < 1 47 - 51 - NO2 -N mg/l < 1 < 1 2,4 – 5,1 TSS mg/l 822 - 895 471 - 578 76 - 90 Color Pt-Co 1178 - 1329 316 - 402 285 - 317 Comments on the research process of leachate treatment by BF method The BF process gives high ammonium and TSS treatment efficiencies in the study range. Although COD and color treatment efficiencies are not high, the output parameters reach VN standards 25: 2009/MONRE column B2. Hence, BF method can be an good option to treat leachate after EC treatment. Research results show that in order to remove COD and ammonium, we can choose an aeration/non-aeration mode is 60/60 minutes, however, under this mode the output concentration of high nitrate, total nitrogen exceeds the norm. To nitrogen concentration after BF process meets VN standards 25: 2009/MONRE column B2, the aeration/non-aeration mode must be 15/105 minutes and the input ammonium load can not exceeding 0.16 kg/m3.day. Comments on the research process of leachate treatment by EC method in combination with BF
26. 24 Research results show that the possibility of leachate treatment by BF after the EC treatment process is undeniable. EC process gives a low ammonium and TSS treatment efficiencies. Meanwhile, research results show that BF process has high ammonium and TSS treatment efficiencies. Hence, the parameters with low removal efficiency in EC process are handled well by BF process. The combination of EC and BF processes in leachate treatment of Nam Son landfill is feasible because the several pollutants concentration after both processes meets VN standards 25: 2009/MONRE column B2. CONCLUSION AND RECOMMENDATIONS CONCLUSION The study results have achieved the objectives of the thesis as follows: 1. Determining suitable conditions for the electrocoagulation process by iron electrodes are: J = 3,896 mA / cm2, electrolysis time = 60 minutes, initial pH = 7 - 8, electrodes distance = 1 cm, then COD, ammonium, TSS and color treatment efficiencies reach 72-77%, 23 - 25%, 38 - 40% and 71 - 72% respectively. The electrocoagulation process improves the BOD5/COD ratio from about 0.32 to 0.42, which is a good condition for biological treatment. 2. COD, TSS and color treatment efficiencies in leachate by iron electrodes being higher than aluminum electrodes are 31.96; 11.51 and 4.35% respectively. Meanwhile, the ammonium removal efficiency by aluminum electrodes is 2.82% higher than that of iron electrodes. 3. Determine the energy consumption demand for the process of electrolytic flocculation for the leachate water of the Nam Son burial site at the above condition of 12.83 KWh/m3 (≈ 1 USD). 4. Determining suitable conditions for COD, ammonium, TSS and color treatment in leachate after the electrocoagulation process by bio- filter system are: aeration/non-aeration time is 15/105 minutes, the input ammonium load does not exceed 0.16 kg/m3.day. Treatment efficiencies of COD, ammonium, TSS and color are 73.77 ± 0.65; 98.88 ± 0.01; 83.34 ± 0.53 and 16.70 ± 0.75% correspondingly. 5. Studied and operated the model in the laboratory using a combination of electrocoagulation and submerged bio-filter system to treat leachate from Nam Son landfill and post-treated wastewater meets VN standards 25: 2009/MONRE column B2. The combination of electrocoagulation process and bio-filter system has the efficiencies of treating COD, ammonium, TSS and color is about 91.70; 97.77; 87.65 and 75.89% respectively. RECOMMENDATIONS Due to the limited research scope of the thesis, the results of the thesis are the basic studies applied combining electrocoagulation with bio-filter system in leachate treatment. In order to be able to apply this method in practice, further studies are needed to perfect the electrocoagulation and bio-filter techniques in leachate treatment. Some of the recommendations made by the author are as follows: 1) Further surveys with some other electrodes to treat leachate by electrocoagulation technique. 2) Building and operating a pilot model to initially evaluate the economic efficiency of this method.
27. 25 NEW CONTRIBUTIONS OF THE THESIS New contributions of the thesis on science and technology: 1/ Determine the effective of EC process by iron electrodes compared to aluminum electrodes to treat pollutants (COD, ammonium, TSS and color) in leachate in Vietnam. 2/ Successful combining the EC process with BF system for effective treatment of contaminants (COD, ammonium, TSS and color) in leachate at laboratory scale. LIST OF PUBLISHED WORKS RELATED TO THE THESIS 1. Le Cao Khai, Le Thanh Son, Trinh Van Tuyen, Doan Thi Anh, Study on leachate treatment after electrocoagulation by bio-filter system (Case study in Nam Son landfill, Hanoi), Journal of Science and Technology, Volume: 55, No. 4C (2017) 251-257. 2. Le Cao Khai, Trinh Van Tuyen, Le Thanh Son, Doan Tuan Linh, Dao Thi Dung, Study on removing color and TSS of Nam Son landfill leachate by electrococagulation process, Journal of Analytical Sciences, Volume: 24, No. 1 (2019) 197-201. 3. Le Cao Khai, Trinh Van Tuyen, Phan Do Hung, Effect of operating conditions on treatment efficiency of an improved anaerobic – anoxic – oxic bio-filter system, Proceedings of the first VAST-BAS workshop on science and technology, (2014) 587-596. 4. Le Thanh Son, Le Cao Khai, Nguyen Thi Ha, Đoan Tuan Linh, Đoan Thi Anh, Electrocoagulation for ammonium removal in Nam Son landfill leachat, VNU Journal of Science: Earth and Environmental Sciences, Vol. 33, No. 2 (2017) 71-77. 5. Le Thanh Son, Le Cao Khai, Doan Tuan Linh, Doan Thi Anh, Effect of some effective parametes on COD removal from Nam Son landfill leachate by electrocoagulation, Journal of Science and Technology, Volume: 55, No. 5 (2017) 540-547. 6. Le Thanh Son, Le Cao Khai, Study on applying advanced oxidation process for removing color of Nam Son landfill leachate after electro-coagulation pretreatment, TNU Journal of Science and Technology, (2019) 204(11) 199- 203. 7. Le Thanh Son, Le Cao Khai, Reduction of COD in Nam Son landfill leachate by electro-Fenton as secondary Pretreatment, Journal of Science and Technology (2019) (Accepted).