Development of Wastewater Treatment System with Low Greenhouse Gases Emission for Natural Rubber Industry

Transcription

1 Development of Wastewater Treatment System with Low Greenhouse Gases Emission for Natural Rubber Industry H. Sonaka*, Y. Muro**, Z. Kimura**, K. Syutsubo***, T. Yamaguchi****, M. Hatamoto*****, D. Tanikawa** * Advanced Architecture and Civil Engineering Course, National Institute of Technology, Kure College, , Aga-minami, Kure, Hiroshima, Japan ( ashow33@gmail.com) ** Department of Civil and Environmental Engineering, National Institute of Technology, Kure College, , Aga-minami, Kure, Hiroshima, Japan ( z-kimura@kure-nct.ac.jp, tanikawa@kure-nct.ac.jp) *** Center for Regional Environmental Research, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba, Ibaraki, Japan ( stubo@nies.go.jp) **** Department of Science of Technology Innovation, Nagaoka University of Technology, 163-1, Kamitomioka, Nagaoka, Niigata, Japan ( ecoya@vos.nagaokaut.ac.jp) ***** Department of Civil and Environmental Engineering, Nagaoka University of Technology, 163-1, Kamitomioka, Nagaoka, Niigata, Japan ( hatamoto@vos.nagaokaut.ac.jp) Abstract In this study, a laboratory-scale experiment was conducted on a combined system comprising an anaerobic baffled reactor (ABR) and a down-flow hanging sponge (DHS) reactor (ABR-DHS system) for treating wastewater discharged from natural rubber industries. Diluted latex that contains 2, mgcod/l (where COD stands for chemical oxygen demand) of acetic acid, 3, mgcod/l of propionic acid, and 25 mgn/l of ammonium nitrogen was used as the synthetic natural-rubber-processing wastewater in this experiment. The ABR-DHS system achieved a COD removal efficiency of 98.5% with an organic loading rate of 3.1 kgcod/(m 3 day). In addition, the DHS effluent achieved both Malaysian and Vietnamese (B) effluent standards of ph, COD, and total nitrogen and ammonia concentrations. In the ABR, approximately 4% of the inlet COD was converted to methane during days 7 to 142. On estimating the greenhouse gas (GHG) mitigation efficiency, we observed that the ABR-DHS system can reduce 46 million t-co 2e /year of GHG emission. Therefore, the developed system can be applied to appropriate treatment technology to achieve the effluent standard in Southeast Asia with low GHG emission and energy recovery. Keywords Natural-rubber-processing wastewater; anaerobic baffled reactor (ABR); down-flow hanging sponge (DHS) reactor; greenhouse gas mitigation INTRODUCTION The natural rubber (NR) industry is one of the major agro-industries in Southeast Asia. NR wastewater contains high concentrations of chemical oxygen demand (COD) and nitrogen due to the presence of residual rubber, organic acids, and ammonia (Nguyen & Luong 212). In Southeast Asia, conventional lagoon system is used for wastewater treatment (Mara, 24). However, this system has some disadvantages such as difficulty in achieving the discharge standard and emission of a large amount of greenhouse gases (GHGs), e.g., methane and nitrous oxide. The nitrous oxide released during NR wastewater treatment has an especially large greenhouse effect (Tanikawa et al. 216a). Furthermore, pre-treatment (e.g., rubber trap and dissolved air floatation) is required so as to prevent the coagulation of rubber and clogging of pipes in the wastewater treatment reactor. The anaerobic baffled reactor (ABR) is one of the anaerobic biological treatment systems that can separate the anaerobic degradation process to each compartment (Barber & Stuckey, 1999). The down-flow hanging sponge (DHS) reactor was developed as an energy-efficient and high-performance aerobic biological treatment process (Tawfik et al. 26). In this study, a laboratory-scale treatment experiment using an ABR-DHS system was conducted with the aim of evaluating this system s performance for treating NR-processing wastewater. Furthermore, the GHG emission reduction efficiency of the ABR-DHS system was estimated.

2 MATERIALS AND METHODS Operational condition of the ABR-DHS system A schematic of the lab-scale ABR-DHS system is shown in Figure 1. The ABR-DHS system comprises an ABR and a DHS reactor, both of which are made of polyvinyl chloride (PVC) pipes (diameter: 65 mm). The ABR comprises four compartments and has a total effective volume of 6.3L. The DHS reactor was filled with polyurethane sponges as media of.4 L. The hydraulic retention times (HRT) of the ABR and the DHS reactor were fixed at 3.4 and.2 days, respectively. The HRT of the DHS was calculated based on the sponge volume. The ABR was inoculated with 2 L of granular sludge from a up-flow anaerobic sludge blanket (UASB) reactor that treated the wastewater from a food factory. The sponge media in the DHS reactor was not inoculated. An air pump (GX7N-2, Gex) was used to supply air to the DHS. The ABR-DHS system was operated at 3 C in a temperature-controlled room. The synthetic NR wastewater used for the experiments was made by mixing NR latex, acetic acid, propionic acid, and ammonia; these particular components were selected based on the characteristics of the present study (Syutsubo et al. 215). The synthetic wastewater contains 4, mgcod/l of NR latex, 2, mgcod/l of acetic acid, 3, mgcod/l of propionic acid and 25 mgn/l of ammonium nitrogen. The ABR-DHS system was operated with an organic loading rate (OLR) of kgcod/(m 3 day). The OLR of the system was increased step-by-step by diluting the influent wastewater. P Influent Gas meter Desulfurizer DHS P Wastewater tank ABR Figure 1 A schematic of the ABR-DHS system Effluent Microbial activity analysis The methane-producing activity (MPA) of the sludge retained in the ABR was determined by measuring the microbial activity. Sample sludge was collected from each compartment of the ABR at day 125. Each sludge sample was washed with a 25-mmol/L phosphate buffer to remove the extra substrate. Then, the sludge was dispersed using a homogenizer (T25, IKA). H 2 /CO 2 (8:2, v/v) at 1.4 atm, 2, mgcod/l of acetate, and 2, mgcod/l of propionate were used as test substrates. The detailed procedure has been described in previous studies (Harada et al. 1994). Analytical method The water quality analysis of the influent, ABR effluent, and DHS effluent was conducted 1 2 times per week. The nitrate concentration, ph, and gas production rate were measured by a nitrate meter (B-743, Horiba), ph/orp meter (KP-1Z, KRK), and wet-type gas meter (WS-1A, Shinagawa) respectively. The COD, total nitrogen (TN), ammonia, and nitrite concentrations were analyzed using a Hach apparatus (DR/25, Hach). The analysis of the volatile suspended solids was done according to the standard method (APHA, 25). The hydrogen, nitrogen, methane, and carbon dioxide concentration in the biogas from the ABR after desulfurization was analyzed by a

3 gas chromatograph (GC-8A, Shimadzu) equipped with a thermal conductivity detector, whereas the nitrous oxide concentration in the biogas was analyzed by a gas chromatograph (GC-8A, Shimadzu) equipped with an electron capture detector. The volatile fatty acid (VFA) concentration was analyzed by a gas chromatograph (GC-14B, Shimadzu) equipped with a flame ionization detector. RESULTS AND DISCUSSION Process performance of the ABR-DHS system The time course of the OLR and COD removal efficiency of the ABR-DHS system are shown in Figure 2. During phase 1 (days 1 to 7), the ABR-DHS system was operated at an OLR of.5 ±.2 kgcod/(m 3 day) to stabilize the COD removal. After phase 1, the OLR of the ABR-DHS system was increased by decreasing the dilution rate of the wastewater (phase 2). During phase 2, the average COD removal of the ABR-DHS system was 96.5% ± 2.4%. The ABR-DHS system achieved a high COD removal efficiency of 98.5% ± 2.4% with an OLR of 3.1 ±.3 kgcod/(m 3 day). The treatment performance was equal to or higher than the previous treatment system for NR-processing wastewater (Nguyen and Luong, 212; Tanikawa et al. 216b; Watari et al., 217). In the ABR, approximately 4% of the inlet COD was converted to methane during days 7 to 142. The converted methane is approximately equal to inlet organic acids as COD. In the ABR, rubber accumulation and pipe clogging were not observed during the entire experimental period. The water quality of the DHS effluent, along with the respective effluent standards, is shown in Table 1. The DHS effluent achieved both Malaysian and Vietnamese (B: QCVN1: 28/BTNMT) effluent standards for ph, COD, TN, and ammonia concentrations. Phase 1 Phase OLR (kgcod/(m 3 day)) COD removal Time (days) Figure 2 Time course of OLR and COD removal efficiency of the ABR-DHS system Table 1 Water quality of the DHS effluent and the effluent standards Parameter Unit ABR-DHS effluent Effluent standard Average ± S.D.* Malaysia Vietnam B ph ± COD mg/l 196 ± TN mgn/l 51 ± Ammonium nitrogen mgn/l 24 ± *S.D.: Standard deviation OLR COD removal (%)

4 The profile of COD concentration in the DHS is shown in Figure 3. COD concentration decreased rapidly in the upper part of the DHS, whereas it decreased at a constant rate in the middle and bottom parts of the DHS. Furthermore, the accumulation of rubber fractions on the surface of the sponge in the upper part of the DHS was confirmed. These results indicate that HRT of the ABR was not enough to coagulate the residual rubber, and the DHS played the roles of both a rubber trap and a biological treatment reactor. Therefore, a short HRT of the ABR can achieve a high-rate treatment along with methane recovery from the degradable substrate in the NR wastewater and can prevent clogging of the reactor owing to coagulated rubber. COD concentration (mg/l) 5 1, 1,5 2, 2,5 2 Flow distance (cm) Figure 3 Profile of COD concentration in the DHS Microbial activity in the ABR Figure 4 shows the MPA on day 125 for the sludge retained in each compartment of the ABR. For all substrates, the highest MPA was observed in compartment 2. Moreover, the hydrogen-fed MPA was times higher than the other substrates. The profile of VFA concentration in the ABR is shown in Figure 5. A rapid decrease of 86% was observed in the concentration of propionate between compartments 1 and 2, indicating that it degraded to acetate, hydrogen, and/or carbon dioxide between compartments 1 and 2. Further, the degraded substrates were converted to methane in compartment 2. MPA (gcod/(gvss day)) H2/CO2 2 2 MPA (gcod/(gvss day)) Compartment No. Compartment No. Figure 4 Methane-producing activity (MPA) in the ABR retained sludge at day Propionate Acetate

5 Concentration (mgcod/l) 1,5 1, 5 Propionate Acetate Inf Eff. Figure 5 Profile of VFA concentration in the ABR Estimation of GHG emission from the ABR Throughout the experiments, no the nitrous oxide production from the ABR was observed. Based on this observation, GHG emission reduction efficiency was calculated, and the results are shown in Table 2. It is an assumed calculation, but if the ABR-DHS system is introduced in all the rubber-processing factories in Vietnam, it can reduce the GHG emission by 46 million t-co 2e /year compared to emissions arising from the conventional lagoon system in Vietnam. This value is approximately equivalent to 1.1% of the total GHG emissions from the agro-industry in Southeast Asia during 214 (FAOSTAT, 217). GHG emission rate from methane in biogas GHG emission rate from dissolved methane GHG emission rate from nitrous oxide Table 2 GHGs emission from previous studies and the ABR Conventional Units lagoon system in Vietnam UASB t-co 2e /m 3 -wastewater (ww).54 a Can be recovered as energy ABR Can be recovered as energy t-co 2e /m 3 -ww Not measured Not measured.18 t-co 2e /m 3 -ww.99 a.45 Not detected Total GHG emission million t- CO 2e /year 46 * 1.4 *.53 * (Tanikawa et al. (Watari et al., References (this study) 216a) 217) * Total GHG emission was calculated using the GHG emission rates, discharge of wastewater from rubber product (3 m 3 -ww/t-product, Nguyen and Luong, 212), and natural rubber production (1 million t-product/year, Based on FAOSTAT data obtained during 214). CONCLUSION In this study, a laboratory-scale experiment was conducted on an ABR-DHS system used for treating wastewater discharged from the NR industry. The ABR-DHS system achieved a COD removal efficiency of 98.5% with an OLR of 3.1 kgcod/(m 3 day) and achieved both Malaysian and Vietnamese (B) effluent standards. In the ABR, degradable substrates such as VFA were degraded and got converted into methane. On the contrary, residual rubber in the synthetic wastewater was trapped in the upper part of the DHS. Therefore, the DHS served as both a rubber trap and a biological treatment reactor. These results suggest that residual rubber recovery by DHS can prevent rubber coagulation in an ABR with short HRT, thus enabling efficient treatment of the

6 NR wastewater with resource recovery. GHG emission rate from the ABR-DHS system was very low during the entire experimental period. Estimation of the GHG emission reduction efficiency indicates that the implementation of ABR-DHS system can reduce up to 1.1% of GHG emission from the agro-industry in Southeast Asia. Therefore, the ABR-DHS system can be applied to the NR wastewater treatment system to achieve the effluent standards in Southeast Asia with low GHG emission and high energy recovery. ACKNOWLEDGEMENT This work was supported by JSPS KAKENHI Grant Number 16K18176 and Iwatani Foundation s Research Grant. REFERENCES APHA 25 Standard Methods for the Examination of Water and Wastewater, 2th edn. American Public Health Association/American Water Works Association/Water Environment Federation, Washington, DC, USA. Barber, W. P., & Stuckey, D. C The use of the anaerobic baffled reactor (ABR) for wastewater treatment: a review. Water Research, 33(7), FAOSTAT: Food and agriculture organization of the United Nations statistics division, (8 July 217) Harada, H., Uemura, S., & Momonoi, K Interaction between sulfate-reducing bacteria and methane-producing bacteria in UASB reactors fed with low strength wastes containing different levels of sulfate. Water Research, 28(2), Mara, D. (213). Domestic wastewater treatment in developing countries. Earthscan Publications, London, England. Nguyen, H., N., & Luong T., T. 212 Situation of wastewater treatment of natural rubber latex processing in the Southeastern region, Vietnam, Journal of Vietnamese Environment, 2(2), Syutsubo, K., Tanikawa, D., Watari T., Fukuda, M., N., B., Nguyen, & Yamaguchi, T. 215 Survey of process performance and greenhouse gases emission of waste water treatment system in natural rubber processing factories, Proceedings International Rubber Conference 215, Tanikawa, D., Syutsubo, K., Hatamoto, M., Fukuda, M., Takahashi, M., Choeisai, P. K., & Yamaguchi, T. 216b Treatment of natural rubber processing wastewater using a combination system of a two-stage up-flow anaerobic sludge blanket and down-flow hanging sponge system. Water Science and Technology, 73(8), Tanikawa, D., Syutsubo, K., Watari, T., Miyaoka, Y., Hatamoto, M., Iijima, S., Fukuda, M., N. B. Nguyen, & Yamaguchi, T. 216a Greenhouse gas emissions from open-type anaerobic wastewater treatment system in natural rubber processing factory. Journal of Cleaner Production, 119, Tawfik, A., Ohashi, A., & Harada, H. 26 Sewage treatment in a combined up-flow anaerobic sludge blanket (UASB) down-flow hanging sponge (DHS) system. Biochemical Engineering Journal, 29(3), Watari, T., Mai, T.C., Tanikawa, D., Hirakata, Y., Hatamoto, M., Syutsubo, S., Fukuda, M., Nguyen, N.B. & Yamaguchi, T. 217 Performance evaluation of the pilot scale upflow anaerobic sludge blanket downflow hanging sponge system for natural rubber processing wastewater treatment in South Vietnam. Bioresouce Technology, 237,