Research on the leachate treatment by electrocoagulation method combined with biological filtration

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 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 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 electrolysis time on COD treatment efficiency Figure 3.2. Effect of current density and electrolysis time on ammonium treatment efficiency 6Figure 3.3. Effect of current density and electrolysis time on TSS treatment efficiency Figure 3.4. Effect of current density and electrolysis time on 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 time (mins) Treatment efficiency (%) 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 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. Thoi 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. Current intensity (A) Current density (mA/cm2) Potential (V) Power consumption (KWh/m3) COD treatment efficiency (%) Ammonium treatment efficiency (%) TSS treatment efficiency (%) Color treatment efficiency (%) 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). 8Figure 3.6. Effect of initial pH on COD treatment efficiency Figure 3.7. Effect of initial pH on ammonium treatment efficiency Figure 3.8. Effect of initial pH on TSS treatment efficiency Figure 3.9. Effect of initial pH on 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) pH Treatment efficiency (%)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 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 distance on COD treatment efficiency Figure 3.11. Effect of electrodes distance on ammonium treatment efficiency Figure 3.12. Effect of electrodes distance on TSS treatment efficiency Figure 3.13. Effect of electrodes distance 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 distance (cm) Treatment efficiency (%) 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 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 on COD treatment efficiency by iron electrodes in comparison with aluminum electrodes Figure 3.15. Effect of electrolysis time on ammonium treatment efficiency by iron electrodes in comparison with aluminum electrodes Figure 3.16. Effect of electrolysis time on TSS treatment efficiency by iron electrodes in comparison with aluminum electrodes Figure 3.17. Effect of electrolysis time on color treatment efficiency by iron electrodes in comparison with 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. 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) Electrolysis time (mins) Treaatment efficiency (%) COD Amoni TSS Color 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 treatment efficiency with iron and aluminum electrodes Figure 3.19. Effect of pH on ammonium treatment efficiency with iron and aluminum electrodes 12 Figure 3.20. Effect of pH on TSS treatment efficiency with iron and aluminum electrodes Figure 3.21. Effect of pH on color treatment efficiency with iron and 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) pH Treatment efficiency (%) 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 < 7) and alkaline (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 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 distance on COD treatment efficiency in comparison iron with aluminum electrodes Figure 3.23. Effect of electrodes distance on ammonium treatment efficiency in comparison iron with aluminum electrodes Figure 3.24. Effect of electrodes distance on TSS treatment efficiency in comparison iron with aluminum electrodes Figure 3.25. Effect of electrodes distance on color treatment efficiency in comparison iron with aluminum 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 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 distance (cm) Treatment efficiency (%) COD Amoni TSS Color 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. 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 Study Treatment efficiency (%) Enery/m3 leachate (KWh)COD Amonium TSS Color 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. (2014) 53,3 - - 65 - 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 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 Figure 3.26. Effect of aeration modes on COD treatment efficiency 3.2.1.2. Effect of aeration modes on ammonium treatment efficiency Figure 3.27. Effect of aeration modes on ammonium treatment efficiency 3.2.1.3. Effect of aeration modes on nitrate treatment efficiency Mode 1: 60/60 Mode 2: 45/75 Mode 3: 30/90 Mode 4: 15/105 Mode 2: 45/75 Mode 1: 60/60 Mode 3: 30/90 Mode 4: 15/105 17 Figure 3.28. Effect of aeration modes on nitrate treatment efficiency 3.2.1.4. Effect of aeration modes on TSS treatment efficiency Figure 3.29. Effect of aeration modes on TSS treatment efficiency 3.2.1.5. Effect of aeration modes on color treatment efficiency Mode 1: 60/60 Mode 2: 45/75 Mode 3: 30/90 Mode 4: 15/105 Mode 1: 60/60 Mode 2: 45/75 Mode 3: 30/90 Mode 4: 15/105 18 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 Aeration/non- aeration mode (mins) Treatment efficiency COD (%) Amonium (%) Outlet nitrate (mg/l) TSS (%) Color (%) Mode 1 (60/60) 90,64 ±0,88 99,88 ± 0,04 371,87 ± 9,13 84,36 ± 0,66 55,13 ± 1,81 Mode 2 (45/75) 84,91 ±1,17 99,62 ± 0,03 254,5 ± 14,70 87,39 ± 0,52 46,03 ± 1,14 Mode 3 (30/90) 79,54 ±1,00 99,52 ± 0,03 160,32 ± 8,44 89,20 ± 0,57 39,09 ± 1,61 Mode 4 (15/105) 77,45 ±1,31 99,21 ± 0,03 43,64 ± 1,16 91,07 ± 0,52 34,75 ± 1,30 Mode 2: 45/75 Mode 3: 30/90 Mode 1: 30/90 Mode 4: 15/105 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. 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 Mode 4: 3 lít Mode 5: 4 lít Mode 6: 5 lít Mode 7: 6 lít Mode 8: 7 lít 20 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 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 Mode 4: 3 lít Mode 5: 4 lít Mode 6: 5 lít Mode 7: 6 lít Mode 8: 7 lít Mode 4: 3 lít Mode 5: 4 lít Mode 6: 5 lít Mode 7: 6 lít Mode 8: 7 lít 21 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 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 standard