Study on leachate treatment after electrocoagulation process by Bio-Filter system: A case study in Nam Son landfill, Ha noi - Le Cao Khai

Vietnam Journal of Science and Technology 55 (4C) (2017) 251-257 251 STUDY ON LEACHATE TREATMENT AFTER ELECTROCOAGULATION PROCESS BY BIO-FILTER SYSTEM: A CASE STUDY IN NAM SON LANDFILL, HA NOI Le Cao Khai 1, * , Le Thanh Son 2 , Trinh Van Tuyen 2 , Doan Thi Anh 2 1 Department of Chemistry, Hanoi Pedagogical University Number 2, 32 Nguyen Van Linh, Phuc Yen, Vinh Phuc 2 Institute of Environmental Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi * Email: lecaokhaimt@gmail.com Received: 30 June 2017; Accepted for publication: 17 October 2017 ABSTRACT One of the major pollution issues caused by the municipal solid waste landfill is leachate, which creates a huge risks to contaminate groundwater, surface water as well as surrounding land quality. The leachate of Nam Son landfill contains high concentrations of pollutants such as COD, BOD5, NH4 + -N. Hence, this study focused on setting up a bio-filter system and investigating its performance on Nam Son landfill leachate after pre-treatment by electrocoagulation (EC). The characteristics of raw leachate for bio-treatment were as following: pH = 8.7 - 8.9, COD = 1391 – 1492 mg/L, NH4 + -N = 661 - 818 mg/L. The experimental system was set up with use volume of 20 lit (dimension: l = 0.15 m, w = 0.28 m and h = 0.52 m) in conditions: room temperature (25-32 o C) flow rate from 2 – 6 L/day, bio-media had a specific surface of 200 m 2 /m 3 . The experimental results were found that COD treatment efficiency from 78–96 % with input COD load from 0.12 – 0.45 kg/m3/day. The NH4 + -N treatment efficiency from 98–99.9 % with input NH4 + -N load from 0.08 ÷ 0.25 kg/m 3 /day. The research results indicated that the leachate treatment by combination of electrocoagulation and bio-filter system can promise as a potential method in practice. Keywords: bio-filter, leachate, NH4 + -N treatment, COD treatment. 1. INTRODUCTION Landfilling is one of the most popular methods of municipal solid waste disposal because of its relative simplicity and low cost [1]. However, one of the most serious issues existing in all most landfill site is leachate which is made up of rain that passes through a land-fill site and liquids that are generated by the breakdown of the waste within the landfill [2]. The leachates are a mixture of high concentration organic and inorganic contaminants including humic acids, ammonia nitrogen, heavy metals, xenobiotics and inorganic salts, and need to be removed due to their toxicity or unfavourable effect on the environment. Conventional leachate treatment methods, such as air stripping, coagulation, flocculation and settling, are often not achieved the desired effect. Other methods such as reverse osmosis, active carbon adsorption only transfer the Le Cao Khai, Le Thanh Son, Trinh Van Tuyen, Doan Thi Anh 252 pollution and do not solve the environmental problem [3]. Taking in to account the changing nature and composition of leachates depending on age, season, climatic conditions as well as more stringent regulation criteria for leachate discharge, leachate treatment plants are forced to integrate chemical–physical and biological stages [2]. Therefore, this research proposed a bio- filter technique as a secondary leachate treatment method. This landfill leachate was pre-treated by electrocoagulation process before biological treatment. Bio-filtration being a biological treatment process occurs when the polluted water passes through porous media which contain microorganisms being able to treat pollutants. This method has many advantages compared to traditional biological processes such as: takes up less installation area, can adapt well to both load and temperature changes, without separated modules in front of treatment system, can able to resistant to xenobiotic compounds and effective cost. Due to the porous nature of media, the biomass density on the media is very high, leading to a high treatment efficiency. The bio-media can be inorganic compounds (such as glass beads, plastic, clay ...) or organic compounds (peat, peel, compost, activated carbon ...). Bio- filtration systems can be either aerobic or anaerobic, the flow regime being either downstream or upstream. Different types of biofilm reactors have been used for the biological treatment of wastewater. Of which, the submerged filter is a novel system in which total submerged fixed media is used to support biomass growth as a thin biofilm on their surfaces (Shakerkhatibi M. et al., 2010 [4]). There have been several reports on the application of submerged bio-filer system for both municipal and industrial wastewater treatment namely Hamoda et al., 1999 [5]; Nabizadeh et al., 2006 [6] and Izanloo et al., 2006 [7]. In particular, some significant researches concerning the treatment efficiency of landfill leachate by submerged bio-filter reactor has been conducted in the world (A. Matarán et al, 2002 [8]; Gálvez A et al, 2006 [9]; Wang Guen Shim et al., 2012 [10]).This study focused on assessing the bio-filter performance on leachate treatment throughout investigating effect of some operating factors namely aeration mode and loading rate on organic compounds (COD) and ammonium treatment efficiencies. 2. METHODS AND MATERIALS 2.1. Landfill leachate The leachate sample used in this study was taken from Nam Son landfill being one of the most modern and famous landfill in Vietnam and located in Soc Son district, Hanoi city. After collecting from Nam Son leachate reservoir, the samples were pre-treated by electrocoagulation reactor before treatment by bio-filter system. The leachate characteristics were shown in Table 1 2.2. Experimental system The experimental system is shown in Fig. 1. The laboratory bio-filter tank was made by transparent mica with several technical parameters as shown in Table 2. The bio-media was made by polyethylene (PE) with the specific surface area of 200 m 2 /m 3 and was cultured with microorganism. Wastewater was flowed to AO tank. At the bottom of the oxic tank there was a continuous air supply unit to increase the amount of oxygen in the wastewater and create circulation to the anoxictank and simultaneously drag and circulate the sludge in the settling tank. Wastewater after passing the settling tank flowed out into storage devices. Sludge in the settling tank at the time of aeration was automatically pulled back to oxic then anoxic tank. pH, DO parameters Study on leachate treatment after electrocoagulation process by bio-filter system 253 were displayed on the control panel and stored on the computer. Experimental modes were shown in Table 3. Table 1. The characteristics of leachate sample used in the experiment. No Parameter Unit Raw leachate Leachate after EC 1 pH - 8,0 – 8,1 8,7 – 8,9 2 COD mg/L 3374- 3812 1391-1492 3 BOD5 mg/L 1106 - 1317 312 - 410 4 NH4 +-N mg/L 844-1138 661 - 818 5 NO3 - mg/L 2.56- 3.88 0 - 2.0 6 TSS mg/L 3375 - 3827 258 - 310 8 Conductivity mδ/cm 8.6 - 9.4 7.9 - 9.1 9 Color 3595 890 Table 2. Technical parameters of bio-filter system. Technical parameters Unit Anoxic + oxic tanks (AO tank) Settling tank Length m 0.15 0.15 Width m 0.28 0.05 Height m 0.52 0.52 Use volume L 20 3.8 Table 3. Operational modes **, A: Aeration time (min), N: Non-aeration time (min) Mode Operation details Inflow (L/d) DO (mg/L) Aeration mode (min) (A/N**) Temperature (oC) 1 2.0 6.0 – 7.0 60/60 25 – 32 2 3.0 6.0 – 7.0 60/60 25 – 32 3 3.0 6.0 – 7.0 45/75 25 – 32 4 3.0 6.0 – 7.0 30/90 25 – 32 5 4.0 6.0 – 7.0 60/60 25 – 32 6 5.0 6.0 – 7.0 60/60 25 – 32 7 6.0 6.0 – 7.0 60/60 25 - 32 Figure 1. Diagram of bio-filter system ①: Anoxic tank②: Oxictank③: Settling tank④: Sludge vale ⑤: Air blower⑥: Bio-media 2.3. Chemicals and analytical methods Chemicals Equipment Natrisalixylat, Trinatrixytrat, Natridiclorosoxyanurat Natrinitrosopentaxyano iron (III), Mercury sulfate Natrihydroxit, Sulfuric acid, Silver sulfate, EDTA Potassium dichromate solution, Mohr’s salt solution - pH meter, DO (HANNA HI 991001) - Spectrophotometer PD-303S Apel (Japan) - Thermoreactor reactor TR 320 (Merck) Analytical standard: NH4 + -N: TCVN 6179-1:1996, COD: TCVN 6491:1999. Le Cao Khai, Le Thanh Son, Trinh Van Tuyen, Doan Thi Anh 254 3. RESULTS AND DISCUSION 3.1. Effect of aeration modes on COD and NH4 + -N treatment efficiency In order to assess the impact of aeration mode on COD and ammonium treatment efficiency, a series of continuous experiments was carried with flow rate of 3L/day at 3 different aeration modes (mode 2, 3, 4). The volume of this bio-filter system always was fixed at 20 L. The results of the effect of aeration mode on COD treatment efficiency was indicated in Fig. 2. Form Fig. 2, with the average influent COD of approximately 1350 mg/L, at mode 2, the COD treatment efficiency reached about 95 % and the average COD effluent remained around 74 mg/L meeting the limited concentration in category QCVN 25:2009/BTNMT column B1. However, both mode 3 and 4 experienced a small drop in COD treatment efficiency, stayed on approximately 88.4 and 80.5 %, respectively. This result indicated that together with the increase in pause time and decrease in aeration time as well as in DO, the amount of COD removed also reduced, which is on the same trend with the research by Le Cao Khai et al. [11]. In spite of during the same period of sampling time, there was a change in treatment efficiency, the more aeration time, the better organic treatment efficiency. The reason can be that there were not only aerobic and anaerobic microorganisms but also arbitrarily microorganisms. When the aeration time increases, the amount of oxygen in tanks also increases, which is a good condition for aerobic microorganism development. These microorganisms tend to digest organic matter in leachate, hence the COD treatment process reach high efficiency. Besides, the effect of aeration modes on ammonium removal efficiency was indicated in Fig. 3. Figure 3 illustrated that the aeration modes did not have much influence on ammonium treatment efficiency. Although in any aeration mode, with the influent ammonium concentration of around 631 mg/L, after one day treatment, approximately 99 % NH4 + -N removed and the effluent NH4 + -N remained around 1.65 mg/L, totally met the NH4 + -N accepted value in category QCVN 25:2009/BTNMT column A. However, it can be seen clearly that at mode 4, the ammonium treatment efficiency seem to be more stable. So, submerged bio-filter system promised an effective method in NH4 + -N treatment in practice. From the results of aeration mode influence on COD and NH4 + -N removal efficiency, it can be concluded that mode 2 (60 min aeration/60 min pause) would be the best choice for the subsequent experiments. 3.2. Effect of COD and NH4 + -N loading rate on treatment efficiency The series of experiments studying on effect of COD and NH4 + -N loading rate on COD and NH4 + -N treatment efficiency were set up under the conditions: aeration/non-aeration mode = 60/60; pH of influent solution = 8.7 - 8.9; input flow varied from 2 to 6L/day. From Figure 4, when the average COD loading values increased from 0.12 to 0.45 kg/m 3 /day, the COD treatment efficiency reduced gradually by more than 15 %. In particular, with 2L of input leachate per day corresponding to approximately 0.12 kg COD/m 3 /day, nearly 96 % of COD was treated after one day. When the input COD load rose to 0.21 kg COD/m 3 /day, this treatment efficiency dropped to around 93 %. When the input COD loading increased continuously to 0.25, 0.36 and 0.45 kg COD/m 3 /day, the average COD treatment efficiency decreased to about 91.3, 89.5 and 80.2 %, respectively. Study on leachate treatment after electrocoagulation process by bio-filter system 255 Figure 2. Effect of aeration mode on COD treatment efficiency Figure 3. Effect of aeration mode on NH4 + -N treatment efficiency Figure 4. Effect of COD loading rate on COD treatment efficiency Figure 5. Effect of ammonium loading rate on NH4 + - N treatment efficiency Figure 5 showed clearly that the ammonium treatment efficiency by this bio-filter system reached very high, above 98 %. Moreover, the input loading of solution is inversely proportional to ammonium treatment efficiency. This trend can be explained that when the higher load increased, the amount of pollutants also increased, meanwhile the biological productivity of this experimental system didn’t change, then the COD and NH4 + -N treatment efficiencies went down with the increase in loading rate. This result is in line with the research by Ngoc Thuy (2010) [12] that the higher load, the lower nitrification efficiency (occurring in the aerobic compartment). However, when the NH4 + -N input load varied from 0.08 to 0.25 kg /m 3 /day, the NH4 + -N treatment efficiency didn’t change considerably, just from approximately 98.4 to 99.9 %. The research results showed that it can have the ability to remove ammonium effectively at higher loads. It can be concluded from Fig. 4 and 5 that the optimum flow for this bio-filter system was 5 L of leachate per day, corresponding to the COD and NH4 + -N input loads of 0.36 and 0.17 kg/m 3 /day, the COD and NH4 + -N treatment efficiency reached approximately 90 and 99 %, respectively. 10 60 0 500 1000 1500 2000 0 10 20 30 C O D t re at m en t ef fi ci en cy , % C O D , m g /L Time, d COD influent COD effluent COD treatment efficiency Mode 2 ηCOD = 95 % Mode 3 ηCOD = 88.4 % Mode 4 ηCOD = 80.7 % 96.5 97.5 98.5 99.5 0 200 400 600 800 0 10 20 30 N H 4 + -N t re at m en t ef fi ci e n c y , % N H 4 + -N , m g /L Time, d NH4+-N influent NH4+-N effluent NH4+-N treatment efficiency Mode 2 ηNH4+-N = 99.6 % Mode 3 ηNH4+-N = 99.7% Mode 4 ηNH4+-N = 99.9 % 70 75 80 85 90 95 100 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0 10 20 30 40 50 C O D t re at m en t ef fi ci en cy , % C O D l o ad in g r at e, k g /m 3 /d ay Time, d COD loading rate COD treatment efficiency M. 1 M. 2 M. 5 M. 6 M. 7 98.0 98.4 98.8 99.2 99.6 100.0 0 0.05 0.1 0.15 0.2 0.25 0.3 -10 10 30 50 N H 3 -N t re at m en t ef fi ci en cy , % N H 3 -N l o ad in g r at e, k g /m 3 /d ay Time, d NH4+-N loading rate NH4+-N treatment efficiency M 2 M 1 M 5 M. 6 M.7 Le Cao Khai, Le Thanh Son, Trinh Van Tuyen, Doan Thi Anh 256 4. CONCLUSIONS Study on effect of operating modes on COD and ammonium treatment efficiency in pre- treated leachate by submerged bio-filter system showed several results. Firstly, aeration mode was directly proportional to COD removal efficiency whereas it seems to be inverse proportional to NH4 + -N treatment efficiency. When the time ratio in aeration/pause mode changed from 60 min/60 min to 30 min/90 min, the average COD treatment efficiency reduced from 95 to 80.5 %, although the NH4 + -N treatment efficiency didn’t vary significantly, remaining above 99 %. Secondly, an increase in input loads lead to a decrease in treatment performance. The results indicated that the COD removal efficiency was from 78.8 to 96.7 % with COD input load from 0.12 to 0.45 kg/m 3 /day and the NH4 + -N treatment efficiency was found in range of 98.3 to 99.9 % with NH4 + -N input load from 0.08 to 0.25 kg/m 3 /day. Acknowledgements. 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