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MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY 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 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 INTTRODUCTION 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 nonresponding 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 technologies allows optimization of leachate treatment process and posttreatment 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 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 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 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- 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+ + neThese metal cations combine with the OH- ions (present in the water) to form metal hydroxides according to the following reaction equations: Mn+ + 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 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 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 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 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 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 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 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 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: Thoi 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 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 From Table 3.2 shows, as the current density increases, the power consumption increases At current density J = 1,298 mA/cm (I = 1A), the electrical energy consumption is 1.05 KWh/m leachate As increasing to J = 5,194 mA/cm2 (I = 4A), the power consumption increases to 24,67 KWh/m 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/cm does not change significantly compared to J = 4,545 and 5,194 mA/cm The energy consumed to treat m3 of leachate at J = 5,194 mA/cm 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/cm Table 3.2 show that if the current density is smaller than 3,896 mA/cm 2, 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 Current intensity (A) 1,0 2,0 2,5 3,0 3,5 4,0 Current density (mA/cm2) Potential (V) treatment efficiencies COD Ammonium Power treatment treatment consumption efficiency efficiency (KWh/m ) (%) (%) TSS treatment efficiency (%) Color treatment efficiency (%) 1,298 1,9 1,05 53,33 14,03 6,85 42,2 2,597 4,4 4,89 62,50 15,03 20,79 56,5 3,246 5,5 7,64 69,64 18,32 26,57 59,6 3,896 7,7 12,83 76,79 23,64 38,61 71,67 4,545 9,3 18,08 78,71 24,32 39,04 74,27 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) Figure 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 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 cm) Treatment efficiency (%) pH COD Ammonium TSS Color 50,00 14,33 16,65 24,11 69,62 22,02 18,95 40,99 73,91 22,63 30,55 67,1 72,00 24,88 39,93 72,2 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 to 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 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 cm) Treaatment efficiency (%) Electrolysis time (mins) 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 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 cm) Treatment efficiency (%) COD Amoni TSS Color pH Fe Al Fe Al Fe Al Fe Al 50,00 18.72 14.33 15.87 16.65 13.8 24.11 22.5 69.62 35.9 22.02 23.57 18.95 15.24 40.99 35.7 73.92 44.83 22.63 25,56 30.55 22.97 67.04 60.2 72,00 43.58 24.88 26.46 39.93 35.83 72.19 65.13 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 = - and Al: pH = - 6) This result is the basis for selecting the input pH value of the leachate and the appropriate electrode type The initial pH - 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 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 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) Treatment efficiency (%) Electrodes distance COD Amoni TSS Color (cm) Fe Al Fe Al Fe Al Fe Al 76,79 44,83 23,64 26,46 38,61 27,1 71,67 67,32 63,71 30,00 20,38 20,80 27,21 25,71 64,25 55,46 50,00 26,70 14,85 15,60 21,10 18,93 44,42 37,29 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/cm 2, initial pH = - 8, the electrode distance of 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 < 30%, ammonium > 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 COD Amonium TSS Color Thesis 71 - 77 24 - 25 38 - 40 71 - 72 Enery/m3 leachate (KWh) 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) Shivayogimath C.B et al (2014) 65,85 - - - - 53,3 - - 65 - Study Treatment efficiency (%) 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 pH 8,7 – 9,1 COD mg/l 717 - 870 BOD5 mg/l 312 - 337 + NH4 -N mg/l 410 - 484 NO3 -N mg/l