Co-Degestion of food waste and domestic wastewater by using upflow anaerobic sludge blanket (uasb) couped with a microfiltration membrane (mf)

Vietnam Journal of Science and Technology 56 (2C) (2018) 118-125 CO-DEGESTION OF FOOD WASTE AND DOMESTIC WASTEWATER BY USING UPFLOW ANAEROBIC SLUDGE BLANKET (UASB) COUPED WITH A MICROFILTRATION MEMBRANE (MF) Bui Hong Ha1, The Tien Nguyen1, Thanh Tri Nguyen1, Lan Huong Nguyen2, *, Phuoc Dan Nguyen3 1Institute for Tropicalization and Environment (ITE), 57A Truong Quoc Dung Street, Ward 10, Phu Nhuan District, HCMC 2Faculty of Environment – Natural Resources and Climate Change, Ho Chi Minh City University of Food Industry (HUFI), 140 Le Trong Tan, , Tan Phu District, HCMC 3Faculty of Environment and Natural Resources, Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet St., District 10, HCMC *Email: lanhuongba@gmail.com Received: 09 May 2018; Accepted for publication: 21 August 2018 ABSTRACT This study investigated anaerobic co-digestion of food waste (FW) and domestic wastewater (DWW) by upflow anaerobic sludge blanket (UASB) combined with an external microfiltration membrane (MF) - AnMBR. The model was conducted with varying of hydraulic resident time of 72 h, 48 h, 36 h and 24 h in corresponding with varying of flux, respectively, were 47, 70, 94 and 141 L/m2.h. Removal efficiencies of TSS, tCOD, nitrogen and phosphorus were evaluated. The potential of biogas production also was determined. The results showed that removal efficiency of TSS and tCOD at above mentioned fluxes, respectively, reached 96.81 %, 97.04 %, 97.29 % and 98.08 % for TSS and 91.47 %, 89.31 %, 88.70 % and 87.0 % for COD. Also, the yield of biogas production was 0.083 L/gCODremoved, 0.085 L/gCODremoved, 0.105 L/gCODremoved and 0.103 L/gCODremoved, respectively, in corresponding with above mentioned fluxes. This study indicated that application of the lab-scale model of anaerobic membrane bioreactor for co-digestion the mixture of WF and DWW utilized the concentrated stream of membrane module to increase the biogas yield and to reduce amount of waste solid in landfill. Keywords: anaerobic co-digestion, food waste, domestic wastewater, biogas yield, anaerobic membrane bioreactor. 1. INTRODUCTION Nowadays, almost municipal wastewater are treated by aerobic processes resulting in high energy consumption and produced waste sludge as well as unpossibility of recovering nutrients Co-digestion of food waste and domestic wastewater by using up-flow anaerobic sludge blanket 119 (N, P). Meanwhile, anaerobic treatment is preferred because of lower sludge production and energy demand, and the possibility of recovering nutrients from wastewater which can be reused for agricultural purposes [1]. Moreover, anaerobic treatment are considered as an advanced technology for recovery of resources from wastes. However, the main difficulty in anaerobic process is biomass loss and maintain long solids retention times (SRT) to overcome the low growth rates of anaerobic biomass [2]. To overcome above challenges of anaerobic process, Anaerobic Membrane Bioreactor (AnMBR) is applied to maintain high SRT [3,4]. However, the studies about AnMBR for domestic wastewater (DWW) showed that DWW in most developing countries contained low organic matter concentration [5], so that the energy recovery potential through anaerobic processes is not high. Thus, to improve biogas recovery, some researchers found that it can increase the organic load content by mixing wastewater with the organic solid waste which cause many environmental problems, such as contamination of soil, water and air during collection, transportation and landfill [6]. The studies included the co-digestion of food waste with wastewater treatment plant (WWTP) sludge [7], with other organic wastes [8], manure and other agricultural residues [9]. But, to date, only a few studies on co-treating food waste with wastewater used AnMBR were performed, which is considered as an advanced technology. While the present study involved a continuous operation of an AnMBR at lab-scale, treating the wastewater from septic tank and food waste (FW) from the kitchen of Institute for Tropicalization and Environment (ITE). The importance of the joint treatment of WW and FW is the significant reduction of the transport cost and greenhouse gas emissions of the FW from the production site (households) to the final treatment site and reduced CO2 emissions due to transportation of SW as well as maximum biogas yields recovery from organic matters in concentrated stream of membrane module thanks to the anaerobic treatment like investigated in this work. Thus, the aim of this work was to investigate co-digestion of the kitchen FW jointly with domestic wastewater (DWW) on a lab-scale through anaerobic membrane bioreactor technology to maximize the biogas recovery and evaluate removal efficiency of tCOD, TSS, nitrogen and phosphorus of AnMBR system. 2. MATARIALS AND METHODS 2.1. The laboratory-scale AnMBR model Flow diagram of the lab-scale AnMBR in this study was presented in Fig. 1, which is located in Institute for Tropicalization and Environment (ITE). The lab-scale AnMBR is fed with the influent of mixture DWW (after grinding) and FW at ratio of 1L:5g. After pretreatment by filtration through a 0.5 mm space screen rotofilter and homogenization in the containing tank, the wastewater is pumped to the anaerobic reactor (UASB). The lab-scale model mainly consists of a UASB of 10 L total volume (3 L head-space volume) connected to a membrane tank of 9 L total volume each (3L head-space volume) with one flat membrane module (0.05 mm pore size). In order to improve the stirring conditions of the anaerobic reactor, a fraction of the produced biogas from UASB is recycled to membrane reactor. The sludge is continuously recycled through the external membrane tanks, where the effluent is obtained by vacuum filtration and stored in a effluent containing tank. In order to control the solids retention time in the system, a fraction of the sludge is intermittently wasted from the anaerobic reactor throughout the day. The AnMBR membrane operation consists of a combination of different stages based on a filtration– relaxation (F–R) cycle with 8 min of filtration time and 2 min of relaxation time. The anaerobic Bui Hong Ha, The Tien Nguyen, Thanh Tri Nguyen, Lan Huong Nguyen, Phuoc Dan Nguyen 120 reactor is only fed when the filtration phase of the membranes is taking place, in order to maintain the same reactor volume and according to the set HRT. Therefore, the WW containing tank with a pump is necessary to guarantee the AnMBR feed requirements. The stirrer in this tank helps to ensure a homogenized sample when feeding the reactor. It is necessary to homogenize the wastewater to avoid solid sedimentation in the influent containing tank. Figure 1. Flow scheme of AnMBR for co-digestion of DWW and FW. 2.2. Inoculum, feed wastewater, food waste and FW feeding procedure Table 1. The main characterization of mixture of FW and DWW fed to UASB. Parameter Units Mixture of FW and DWW (n=15) HRT = 72 h HRT = 48 h HRT=36 h HRT=24 h pH - 7.41 ± 0.15 7.36 ± 0.08 7.34 ± 0.11 7.35 ± 0.12 COD mg/L 2031.9 ± 48.7 1989.5 ± 37.6 1882.1 ± 62.9 2064.9 ± 61.6 TSS mg/L 603.5 ± 80.0 623.8 ± 102.8 667.6 ± 82.3 606.0 ± 65.9 TN mg/L 242.1 ± 23.0 235.6 ± 21.4 239.1 ± 22.1 201.3 ± 9.3 TKN mg/L 201.7 ± 19.2 196.3 ± 17.8 200.6 ± 18.3 167.8 ± 7.7 N-NH4+ mg/L 161.4 ± 15.4 157.0 ± 14.3 159.4 ± 14.8 134.2 ± 6.2 P-PO43- mg/L 8.9 ± 0.15 8.8 ± 0.17 8.8 ± 0.10 8.8 ± 0.14 Primary anaerobic sludge was collected from Anaerobic Bioreactor of the wastewater treatment plan of Thien Huong Food Joint Stock Company in Tan Thoi Hiep ward, District 12, HCMC, Viet Nam. Feed wastewater was taken from collection tank of ITE. Food waste was also collected from kitchen of ITE. Then, FW was ground into small particles and mixed with DWW at ratio of 5g:1L of FW and DWW that was determined by considering that an inhabitant equivalent generated 100 L of WW and 0.5 kg of FW per day in Viet Nam before being fed to the reactor (data from investigation in practical about discharge of army billet in Viet Nam). Co-digestion of food waste and domestic wastewater by using up-flow anaerobic sludge blanket 121 In order to prevent damage to the membranes, the FW was filtered through a 0.5 mm sieve-size rotofilter. The filtered FW was stored in the containing tank, which was equipped with a stirrer and membrane diffusers for homogenization and fat removal, respectively. The influent parameters of AnMBR were presented in Table 1. 2.3. Operational conditions of AnMBR The lab-scale model was operated for 120 days with varying of HRT at 72, 48, 36 and 24 h according to the operational conditions shown in Table 2. Operational time period of each HRT was 30 days. Table 2. The operational conditions of AnMBR. Operational parameters Operational conditions HRT (h) 72 48 36 24 Flux (L/m2.day) 47 70 94 141 Wastewater Flow (L/d) 5 7.5 10 15 Amount of Solid Waste (g/d) 25 37.5 50 75 Temperature (0C) 28-35 28-35 28-35 28-35 Organic Loading Rate (OLR-kg COD/m3.day) 0.66 1.02 1.38 2.06 2.4. Analysis To evaluate the performance of the biological process, the following parameters were analysed once 2 days for the mixture of DWW and FW in influent and effluent of AnMBR system: pH, Total Suspended Solids (TSS), Chemical oxygen demand (COD), Total Kjeldahl Nitrogen (TKN), ammonium (N-NH4+) and orthophosphate (P-PO43-). All parameters were determined according to Standard Methods [10]. Measurement of Biogas Yield Figure 2. Mariot equipment for measurement of generated biogas from AnMBR. Bui Hong Ha, The Tien Nguyen, Thanh Tri Nguyen, Lan Huong Nguyen, Phuoc Dan Nguyen 122 The biogas generated from AnMBR was measured by Mariot equipment (Fig. 2). The operational principle of Mariot was described as follows: Biogas from the glass tube increases the pressure when the pressure in the tank is greater than the atmospheric pressure. In order to equilibrium the pressure, the water in the jug starts to flow with an exactly amount same as the influent biogas. When the equilibrium water pressure is completely absent, the pressure of a layer of water equal to the width of the water hole can not escape. 3. RESULT AND DISCUSSION In this study, pH was measured everyday. The results showed that pH in the influent and effluent of the AnMBR were stable in range between 7.34-7.41. This pH was suitable for biological anaerobic treatment of mixture of FW and DWW. 3.1. Removal efficiency of COD The AnMBR was operated by gradually increasing the OLR via a decrease in the HRT of the UASB reactor from 72 h to 24 h. Fig. 3, 4 presented the tCOD of the influent and effluent of the AnMBR and the removal efficiency of tCOD. The HRT varied between 72 h and 24 h during the period with recirculation. The influent tCOD were 2031.9 ± 48.7 mg/L; 1989.5 ± 37.6 mg/L; 1882.1 ± 62.9 mg/L and 2064.9 ± 61.6 mg/L in corresponding with HRT of 72 h, 48 h, 36 h and 24 h, respectively. The removal efficiencies of tCOD reached, respectively, 91.47 %, 89.31 %, 88.7 % and 87 %. The results showed that the total removal efficiency of COD was similar at different HRT and OLR tested, this can be due to the presence of the membrane module [6]. The obtained total removal efficiences were nearly 90 %, with tCOD values in the permeate ranging between 173.7 mg/L, 213.0 mg/L, 233.4 mg/L and 269.9 mg/ in four study periods. The results agreed with results obtained by Gouveia et al. [6]. The obtained results in this study confirmed that AnMBR have high efficiencies in tCOD removal and tCOD removal efficiency nearly did not depend on HRT. Figure 3. tCOD in influent and effluent at varying of HRTs. Figure 4. The removal efficiency of tCOD at varying of HRTs. 3.2. Removal efficiency of TSS 0 100 200 300 400 500 600 1000 1200 1400 1600 1800 2000 2200 1 3 5 7 9 11131517192123252729 tC O D ef flu en t ( m g/ l) tC O D in flu en t ( m g/ L) Time (d) In-72h In-48h In-36h In-24h Out-72h Out-48h Out-36h Out-24h 75 77 79 81 83 85 87 89 91 93 95 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 tC O D re m o v a l (% ) Time (d) HRT 72h HRT 48h HRT 36h HRT 24h Co-digestion of food waste and domestic wastewater by using up-flow anaerobic sludge blanket 123 The changes of TSS over time and TSS removal efficiency were presented in Fig 5. From Fig. 5, TSS in permeate at varying of HRT of 72, 48, 36 and 24 h almost were negligible, reached, respectively, 19.7 mg/L, 18.7 mg/L, 18.5 mg/L and 11.9 mg/L. The results were probably due to presence of membrane module. Figure 5. Removal efficiency of TSS at varying of HRTs. 3.3. Nitrogen and phosphorus removal Nitrogen and phosphorus removal of AnMBR were evaluated by changes of TKN, N-NH4+ and P-PO43- over time. The TKN and N-NH4+ were determined in the influent and effluent of the membrane tank. The results were presented in Fig. 6 and Fig 7. Figure6 showed that most of the TKN in the effluent was present in the form of N-NH4+ (≈ 80.0 ± 0.95 % of the TKN). Thus, there was no significant increase in the concentration of N-NH4+ in the effluent of the membrane tank as a result of the treatment process (85.0 ± 2.2 % of the total N-TKN). This increase in nitrogen content throughout the operation of the AnMBR could be due both to the hydrolysis of the accumulated particulate organic matter and also to the cell decay. The results agreed with study of Gouveia et al. [6] about anaerobic treatment of domestic wastewater. Figure 6. The changes of TKN at varying of HRTs. Figure 7. The changes of N-NH4+ at varying of HRTs. Phosphorous concentration underwent a similar trend, with no significant difference between the concentration of P in the influent and effluent of the AnMBR being recorded. Phosphorous concentration negligibly decreased in effluent of membrane tank from 8.86 mg/L, 8.76, 8.81 and 8.84 to 7.32 mg/L, 7.88, 8.1 and 8.47 mg/L, respectively, in corresponding with 0 200 400 600 800 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 TS S (m g/ L) Time (d) Input Output HRT 72h HRT 48h HRT 36h HRT 24h 140 160 180 200 220 240 1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 10 1 10 5 10 9 11 3 11 7 TK N (m g/ L) Time (d) Input Output HRT 72h HRT 48h HRT 36h HRT 24h 120 170 220 1 9 17 25 33 41 49 57 65 73 81 89 97 105 113N - N H 4+ (m g/ L) Time (d) Input Output HRT 72h HRT 48h HRT 36h HRT 24h Bui Hong Ha, The Tien Nguyen, Thanh Tri Nguyen, Lan Huong Nguyen, Phuoc Dan Nguyen 124 HRT of 72 h, 48, 36 and 24 h (data not shown). There was a slight decrease in P-PO43- because P- PO43- was accumulated in biomass, and wasted with excess sludge in UASB [6]. This predictably low removal of nitrogen and phosphorus in the AnMBR could be beneficial if the effluent is to be used for agriculture or irrigation purpose. 3.4 The biogas yield Biogas volume totally generated from UASB was measured by Mariot equipment and was calculated by the obtained biogas volume by removed total COD. The results were shown in Fig. 8. From Fig.8, the obtained biogas yields were 0.083, 0.085, 0.105 and 0.103 L biogas/g tCODremoved in corresponding with HRT of 72, 48, 36 and 24 h, respectively. The results indicated that HRTs were smaller when the obtained biogas yields obtained higher. The results were because of at small HRT, OLR high, removed tCOD was low resulting in a high biogas yield. Figure 8. The volume of biogas per gram COD removed at varying of HRTs. 4. CONCLUSION Co-digestion of domestic wastewater and food waste by AnMBR technology was found to be feasible in tCOD, TSS removal and improved biogas recovery efficiency. The results indicated that tCOD, TSS removal efficiencies reached nearly 90 % for tCOD and more than 90 % for TSS due to presence of membrane module. The tCOD, TSS removal efficiencies did not much depend on HRTs, also probably due to presence of membrane resulting in long SRT maintained in AnMBR system. Additionally, biogas yields also significantly improved when HRT decreased and concentrated flow from membrane module was recirculated to UASB. The treatment of mixture of food waste and domestic wastewater by AnMBR that resulting in low COD loss and high nutrient recovery brought benefit for treatment of mixture of wastewater and solid wastes in disperse areas where did not have concentrated wastewater treatment plants and solid waste collection systems. Acknowledgment. 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