Treatment of Sugar Containing-Low Strength Wastewater at 20 C by Anaerobic Granular Sludge Bed Reactor

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1 Treatment of Sugar Containing-Low Strength Wastewater at 20 C by Anaerobic Granular Sludge Bed Reactor W. Yoochatchaval 1,4*, K. Kubota,1,2, T. Kawai 3, T. Yamaguchi 2, and K. Syutsubo 1 1 Water and Soil Environment Division, National Institute for Environmental Studies (NIES), Ibaraki, Japan 2 Department of Environmental Systems Engineering, Nagaoka University of Technology, Niigata, Japan 3 Planning and Research section, Research Laboratory, Mitsui Sugar Co., Ltd., Kanagawa, Japan 4 Department of Environmental Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi, Bangkok, Thailand. * Corresponding author, wilasinee.yoo@kmutt.ac.th Abstract : To investigate the feasibility of anaerobic wastewater treatment technology for low strength sugar refinery wastewater ( g COD/L), an 8.8 L volume of anaerobic granular sludge bed reactor was operated at 20 C for 400 days. The operation mode was combination of one pass flow (UASB, 50 min) and effluent-recirculation (EGSB, 10 min) mode. The aerobic down-flow hanging sponge (DHS) reactor was installed as a post-treatment. During the started-up period, reactors were fed with synthetic wastewater at overall HRT of 3 hours (anaerobic 2 hours, aerobic 1 hour). After day 85, feed was changed to real wastewater together with supplement of nutrients, trace elements and NaHCO 3. The sufficient COD removal efficiency (85% SD±6.2) and stable process performance were elicited from the granular sludge bed reactor. Also, post-treatment (DHS reactor) offered good quality of effluent (45 mg COD/L, 7 mg BOD/L) and it achieved the discharge standard. Increasing of sulfate concentration of wastewater caused higher contribution of sulfate reducing bacteria for COD removal. The sludge concentration and settleability were well maintained thoroughly. However, floatation of large size granule was observed in the later part of experiment. This phenomenon may attribute to the high growth yield of retained sludge at 20 C. Keyword: Anaerobic treatment, granular sludge bed reactor, low strength, low temperature, sugar refinery wastewater INTRODUCTION Recently, anaerobic wastewater treatment technology such as upflow anaerobic sludge blanket (UASB) has been widely applied for the treatment of industrial wastewater. The main advantage of this system is the high-rate treatment of wastewater, related to the well retainment of anaerobic bacteria in form of biofilm or granular sludge (Lettinga, 1995 and Speech, 1996). Low strength wastewater treatment by UASB reactor usually faces with difficulties in term of sludge granulation and stable operation. In our previous study, novel operational mode of expanded anaerobic granular sludge bed (EGSB) reactor was developed for treating low strength wastewater at ambient temperature with the good process performance (Yoochatchaval et al., 2008a). The concept of this technology is the combination of operational modes between one pass flow mode (UASB) and continuous effluent-recirculation mode (EGSB) in one reactor by the intermittent effluent recirculation system (named Intermittent effluent Recirculation Granular Sludge Bed: IR-GSB). During UASB mode, organic concentration in the sludge bed kept high to activate anaerobic bacteria. In EGSB mode, biogas detachment and sludge granulation are enhanced by hydraulic mixing due to effluent recirculation. Anaerobic treatment technology is popular and commonly used by many countries especially the granular sludge bed system (Lettinga et al., 1993 and van Haandel et al., 1994). However, when only the granular sludge bed system was used for wastewater treatment, the discharge standard of those countries cannot be achieved. Post-treatment system has been recommended by many researchers (Kooijmans et.al., 1986, Draaijer et al., 1992, Schellinkhout et al., 1992). Various types of post-treatment systems have been developed. To choose the appropriate post-treatment, it depends on the quality of influent for post-treatment system (effluent from anaerobic system), quality of effluent from post-treatment system that would be discharged to the reservoirs, land availability, etc. Downflow-Hanging Sponge (DHS) system (aerobic) has Water Practice & Technology Vol 5 No 3 IWA Publishing 2010 doi: /WPT

2 been studied as a post-treatment in pilot and full scale of UASB reactor in the field of sewage treatment (Agrawal et al., 1997, Machdar et al., 2000, Tandukar, 2006). The DHS provides a sufficient process performance for treating of effluent from UASB reactor. Moreover, it is easy to construct, less energy and area required. Moreover, with respect to the sludge management, it is easy for operation and maintenance. The objective of this study is to confirm the process reliability of IR-GSB reactor for treating real low strength industrial wastewater (sugar refinery wastewater), following with curtain type DHS reactor as a post-treatment. Also, changes of physical and microbial characteristics of retained sludge of the IR-GSB reactor under the ambient temperature condition were investigated. MATERIALS AND METHODS Experimental Set-up An 8.8 L volume of anaerobic granular sludge bed reactor was operated for 400 days with g COD/L of sugar containing wastewater (Figure 1). This reactor was inoculated with 20 C grown granular sludge (Yoochatchaval et al., 2008b) and started-up in the combination of UASB and EGSB mode (controlled by timer). The upflow velocity of wastewater was 1.2 m/h during the UASB mode (one pass flow) and increased to 5 m/h at EGSB mode (effluent-recirculation). Operating temperature was controlled at 20 C by the water jacket. During the started up period (phase A), the reactor was fed with synthetic wastewater, composed of sucrose, acetate, propionate and yeast extract in the COD ratio of 4.5: 2.25: 2.25: 1. The hydraulic retention time (HRT) was controlled at 2 hours. Thus, the volumetric loading was about kg COD/m 3 /day. On day 43 (phase B), the feed substrate was changed to the real wastewater from sugar refinery process. The wastewater was concentrated at 34 g COD/L, stocked at -20 C and transported to the laboratory. Before using, it was defrosted and diluted at COD concentration of g/l. Unfortunately, the COD removal efficiency of IR-GSB reactor after feeding with sugar refinery wastewater decreased due to the lack of important basal mineral (such as ammonia). Then, inorganic nutrients, trace elements and NaHCO 3 were added to the feed after day 85 (phase C). The composition of mineral and trace element have been shown in Table 1. To remove the residual organic carbon, the aerobic post treatment process was installed after the! IR-GSB reactor. From the information of previous Figure 1: The schematic diagram of IR-GSB research, the curtain type down flow hanging reactor and DHS reactor sponge (DHS) reactor was selected because of its stable treatment efficiency in lab-scale experiment! 2

3 (Tandukar, 2006). The long triangular polyurethane sponge and a polyvinyl sheet were both a supporting media. The sponges were attached on one side of the polyvinyl sheet by the glue. Length of one sponge unit was 20 cm. The side of the triangle was 3 cm. There were 40 sponges pasted on the curtain, giving a 2 m height and 4.1 L volume. The HRT of the DHS reactor became about 1 hour (56 minutes) based on the total volume of sponge media. Thus, the total HRT of whole system was about 3 hours. Usually, sponge media was directly exposed to air to supply oxygen. In this study, sponge media was placed in the closed container to prevent the emission of hydrogen sulfide. Therefore, to keep the aerobic condition, air was pumped to the DHS reactor container. Before starting up DHS, sponge was made saturated with water and seeded with activated sludge for 1 day (Machdar et al., 2000). Table 1: Mineral composition of feed solution Samplings and Analytical Methods In order to evaluate the process performance, wastewater quality was determined routinely (five times per week). The influent and effluent of the reactors (IR-GSB and DHS) were each sampled. It took about 1 hour for collection the effluent from IR-GSB reactor and 20 minutes for DHS reactor. The water quality analysis was conducted to determine ph, COD MN, COD CR, BOD, volatile fatty acid (VFA), suspended solid (SS) and sulfate. The physical and microbial properties such as sludge concentration (MLSS), sludge volume index (SVI) and methanogenic activity of the retained sludge in IR-GSB reactor were occasionally analyzed following to the standard method. Also, the bacterial community structure of retained sludge was analyzed by DGGE (Denaturing Gradient Gel Electrophoresis) analysis targeting domain Bacterial 16S rdna (Muyzer et al., 1993). Activity Measurement The methanogenic activity and sulfate reducing activity of retained sludge were determined occasionally, in duplicate with 122 ml of serum vial bottles according to previous research (Syutsubo et al., 1997). The sludge samples for the measurement of activity were washed with 25 mm phosphate buffer to remove the extra substrate and disintegrated by a homogenizer (keep anaerobic condition by purging with nitrogen gas). For methanogenic activity measurement, the test substrates were H 2 /CO 2 (80%:20%, V/V), acetate and propionate. To measure the hydrogen-utilizing activity, the vial headspace was filled with H 2 /CO 2 gas at 1.4 atm (142 kpa). The initial concentration of acetate and propionate were 2 g COD/L and 1 g COD/L respectively. For sulfate reducing activity, the test substrates were H 2 /CO 2, acetate and lactate, in the presence of sulfate (600 mg SO 4 2- /L). From the data of SO 4 2- consumption, sulfate reducing activity was calculated. All vials were incubated in a reciprocal-shaker (120 rpm) at 20 C. RESULTS AND DISCUSSION IR-GSB Reactor Performance The IR-GSB reactor was operated for 400 days with low-strength wastewater ( g COD/L) at 20 C. In this study, the reactor was started-up with the kg COD/m 3 /day of OLR which was stepwise increased to kg COD/m 3 /day by the reduction of HRT from 4 hours to 2 hours (Figure 2 (a)).! 3

4 Figure 2: Process performance of IR-GSB and DHS reactor (values in the parenthesis represent the standard deviation) Table 2: Changes in COD removal efficiency and methane recovery based on the influent COD during the different phases of treatment (values in the parenthesis represent the standard deviation)!!! 4

5 During the started up period (phase A; day 0-43), the reactor was fed with synthetic wastewater (mixer of sugar, VFA and yeast extract). Since the reactor was inoculated with anaerobic granular sludge, the started period was apparently shortened. The IR-GSB reactor achieved 95% (SD±2.7) of COD removal efficiency (Figure 2(b) and Table 2). Including with the post-treatment process (DHS reactor), the COD removal efficiency of this system reached up to 97 % (SD±1.8). Methane gas production was NL/day (SD±2.5). After day 43 (phase B), the feeding substrate was changed to the real wastewater from sugar refinery factory. Due to the continuous feed of real wastewater, the COD removal efficiency of the IR-GSB gradually reduced to 80% (SD±7.1) with the decreasing of methane gas production to 9.86 NL/day (SD ± 1.4). The shortage of ammonia (less than 1 mg of NH4-N/L) concentration in the influent and the lowering of ph (to 6.6) of effluent wastewater were confirmed in the IR-GSB reactor (Figure 2(c)). To compensate the unsuitable condition, on day 85 (phase C) the inorganic nutrients (ammonia, etc.), trace elements and NaHCO3 (as ph buffer) were added to the wastewater. Consequently, the better COD removal efficiency (85%, SD± 6.2) and stable process performance were observed in the IR-GSB reactor. The methane gas production reduced to 7.39 NL/day (SD±1.68) with the increment of percent contribution of COD removal by sulfate reducing bacteria (Figure 2 (d)), which was resulted from the increase of sulfate concentration of sugar refinery wastewater (from 50 mg SO42-/L to 110 mg SO42-/L). The sulfate concentration of the effluent from IR-GSB reactor was about 0 to 5 mg SO42-/L throughout the experiment (Figure 2 (d)). The BOD removal efficiency of IR-GSB was maintained at around 80%. However, sometime the total BOD concentration of effluent from IR-GSB reactor reached to mg BOD/L which exceeds the standard value of wastewater-discharge (Figure 2(e)). So, the post treatment of the effluent from the anaerobic granular sludge bed reactor is required. DHS Reactor Performance In the anaerobic treatment of sugar refinery wastewater, sometime treated effluent exceeded the wastewater discharge standard (50 mg COD/L, mg BOD/L). By the connection of the DHS reactor as the post-treatment of the IR-GSB reactor, effluent quality could achieve the discharge standard and became stable. Finally, effluent total COD and BOD were lowered to about 45 mg COD/L and 7 mg BOD/L, respectively. Furthermore, the excess sludge generation was quite low in the DHS reactor as compare with another aerobic process. During the 400 days operation, it was not necessary to withdraw the excess sludge from DHS reactor. Changes in Physical Properties of Retained Sludge in The IR-GSB Reactor Figure 3 shows the behavior of sludge amount and sludge volume index (SVI) in the IR-GSB reactor. There were 10 sampling ports along the reactor height. For the retained sludge amount measurement, samples were taken from port number 1, 2, 3, 4, 6, 7, 8, and 10 of the IR-GSB reactor. Then the sludge concentration of each sample was measured. For the measurement of SVI, sludge samples were taken from port 2 (32 cm height) and port 6 (115 cm height). The settleability of retained sludge from port 2 was slightly deteriorated throughout the experiment. The SVI increased from 18 ml/g SS (day 80) to 25.3 ml/g SS (day 345). However, the deterioration of retained sludge wasn t observed in port 6. The better settleability was confirmed in the later part of the experiment. As a result, the SVI of port 6-sludge became 27.8 ml/ g SS at day 345.! 5

6 Figure 3: Physical property of retained sludge in IR-GSB reactor (SVI and sludge amount) The sludge amount seems to be increased after the started up period, until day 345 it reached to 165 g SS. When the experiment was continued after day 400, the floatation of large size granular sludge and sludge washed-out were observed occasionally. These phenomena may attribute to the high growth yield of retained sludge at low (20 C) temperature (Yoochatchaval et al., 2009). The SEM (scanning electron microscope) observation of granular sludge confirmed the growth of filamentous bacteria on the surface area of retained sludge. Also, microbial structure analysis of retained sludge confirmed the presence of acid forming bacteria, belonging to phylum Firmicutes (such as genus Lactococcus and Anaerovibrio; DGGE band 1 and 2 in Figure 6). The changes in particle size of the retained sludge are shown in Table 3. Sludge sample was taken from port 2 and port 6 occasionally and analyzed by the image analysis (Scion Image, USA) followed to the previous research (Yoochatchaval et al., 2009). From table 3, the average size of granular sludge is expressed in both relative number and relative volume of sample. Interestingly, after the start-up period, decreasing of the average size of retained sludge from port 2 based on the total number and volume was confirmed. On the other hand, average size of the granular sludge at port 6 increased gradually. Furthermore, floatation of the large size (more than 5 mm) granular sludge was observed in the later part of the continuous flow experiment. Continuous operation of IR-GSB reactor at 20 C enhanced the growth of granular sludge, therefore increasing of the size of the retained sludge progressed toward upper side of the reactor. Furthermore, the growth yield and decay rate of retained granular sludge were calculated by following with previous study (Yoochatchaval et al., 2008b). As a result, the granular sludge in the IR-GSB reactor had 0.17 g VSS/g COD of growth yield and per day of decay rate. This growth yield value is clearly higher than that of mesophilic granular sludge. Table 3: Changes in particle size of the retained sludge taken from Port 2 and Port 6 of the IR-GSB reactor! 6

7 Microbial Characteristics of Retained Sludge in the IR-GSB Reactor Methanogenic Activity To investigate the changes in microbial properties of retained sludge, methanogenic activity of the retained sludge was periodically measured (day 43, 204, 112, and 358). When feed was changed to sugar refinery wastewater, the increasing of H 2 /CO 2 -fed activity and decreasing of acetate-fed activity were observed (Figure 4). The increase in hydrogen-fed methanogenic activity on day 112 illustrates the growth of hydrogen producing acid-forming bacteria in the reactor. Interestingly, decreasing of H 2 /CO 2 fed activity after day 112 was possible to imply that the reactor was operated at stable condition. In addition, in the later part of experiment some amount of hydrogen was consumed by sulfate reducing bacteria (SRB). The continuous operation of IR-GSB reactor with sugar refinery wastewater led to the gradual increasing of acetoclastic- methanogen activity, it finally reached to 0.43 g COD/g VSS/day. The propionate-fed activity of the retained sludge was always kept low as compared with methanogens (H 2 /CO 2, acetate). Figure 4: The methane producing activity of retained sludge in the IR-GSB reactor on day 43, 204, 112, and 358 (test temperature: 20 C) Sulfate Reducing Activity The H 2 /CO 2 -utilizing activity of sulfate reducing bacteria (SRB) in the seed sludge (day 0) was 0.05 g COD/g VSS/day which was only one-fifth of methane producing bacteria (MPB) activity (data not shown). Figure 5 shows the comparison of activities between sulfate reducing bacteria (SRB) and Figure 5: The comparison of activity between sulfate reducing bacteria (SRB) and methane producing bacteria (MPB) on day 390! 7

8 methane producing bacteria (MPB) for degradation of intermediates from sucrose on day 390. After long term operation with sugar refinery wastewater, H 2 /CO 2 -utilizing activity of SRB reached to 5 times of MPB activity. This phenomenon is corresponding to the increase in COD consumption (percent contribution) of sulfate reducing bacteria in Figure 2(d). Moreover, the microbial community structure analysis of retained sludge by domain Bacterial 16S rdna- targeted DGGE shows the growth of sulfate reducing Desulfovibrio sp. (band No.4) in the retained sludge after 110 days of operation (Figure 6). Also, presence of Desulfomicrobium sp. (band No. 3) was confirmed. Figure 6: Bacterial profiles analysis of retained sludge from IR-GSB reactor by DGGE CONCLUSIONS The anaerobic granular sludge bed process, operated with the intermittent effluent recirculation system (IR-GSB) under 20 C condition, exhibited excellent process performance for treatment of low-strength sugar refinery wastewater. The good retention of granular sludge was confirmed throughout the experiment. The increasing of hydrogen-fed sulfate-reducing activity and acetate-fed methanogenic activity implied that biomass was able to adapt itself to the sulfate containing sugar refinery wastewater even at unsuitable condition (low strength, low temperature). Long term operation with high sulfate concentration sugar refinery wastewater caused the growth of sulfate reducing bacteria (Desulfovibrio sp. and Desulfomicrobium sp.) in the retained sludge. It is possible to apply this new treatment technology for treatment of sugar refinery wastewater together with supplement of some important nutrient such as ammonia and ph buffer (NaHCO 3 ). In addition, the DHS reactor was effective as the post-treatment of the anaerobic reactor that treated the low-strength industrial wastewater. ACKNOWLEDGEMENT A part of this study was supported by New Energy and Industrial Technology Development Organization (NEDO). This study was also supported by NIES special-research program and by Mitsui Sugar Co., Ltd. The authors are grateful to "#$ Yue Qin Fang for her technical assistance. REFERENCES Agrawal, L.K., Ohashi, Y., Mochida, E., Okui, H., Ueki, Y., Harada, H., Ohashi, A. (1997). Treatment of raw sewage in a temperature climate using a UASB reactor and the hanging sponge cubes process. Water Science and Technology, 36, (6-7), pp ! 8

9 Draaijer, H., Maas, J.A.W., Schaapman, J.E. and Khan, A. (1992). Performance of the 5-MLD UASB Reactor for Sewage Treatment at Kanpur, India. Water Science and Technology, 25, (7), pp van Haandel, A. and Lettinga, G. (1994). Anaerobic Sewage Treatment: A Practical Guide for Regions with Hot Climates. John Wiley & Sons, Inc., Chichester, UK. Kooijmans, J.L. and van Velsen, E.M. (1986). Application of the UASB Process for Treatment of Domestic Sewage under Sub-Tropical Conditions, The Cali Case. AquaTech86. Lettinga, G., Man, de A., van der Last, A.R.M., Wiegant, W., van Kinppenberg, K., Frijns, J. And van Buuren, J.C.L. (1993). Anaerobic Treatment of Domestic Sewage and Wastewater. Water Science and Technology, 27, (9), pp Lettinga, G. (1995). Anaerobic digestion and wastewater treatment systems. Antobie van Leeuwenhoek, 67, Machdar, I., Sekiguchi, Y., Sumino, H., Ohashi, A. and Harada, H. (2000). Combination of a UASB Reactor and a Curtain-type DHS (Downflow Hanging Sponge) Reactor as a Cost-effective Sewage Treatment System for Developing Countries. Water Science and Technology, 42, (3-4), pp Muyzer, G., de Waal C.E. and Uitterlinden, G.A. (1993). Profiling of complex microbial population by denaturing gradient gel electrophoresis analysis of polymerase chain reaction-amplified genes coding for 16S rrna. Appl. Environ. Microbiol., 59(3), Schellinkhout, A. and Collazos, C.J. (1992). Full-scale application of UASB technology for sewage treatment. Water Science and Technology, 39, (5), pp Speece, R.E. (1996). Anaerobic Biotechnology for Industrial Wastewater. Archae Press, Nashville Tennessee. Syutsubo, K., Harada, H., Ohashi, A. and Suzuki, H. (1997). An effective start-up of thermophilic UASB reactor by seeding mesophilic-grown granular sludge. Water Science and Technology, 36, (6-7), pp Tandukar, M. (2006). Development of Self-sustainable Municipal Sewage Treatment System Consisting of UASB and DHS (Down-flow Hanging Sponge) Reactors for Developing Countries. PhD thesis, Department of Environmental Systems Engineering, Nagaoka University of Technology. Yoochatchaval, W., Nishiyama, K., Okawara, M., Ohashi, A., Harada, H. and Syutsubo, K. (2008a). Influence of effluent-recirculation condition on the process performance of EGSB reactor for treating of low strength wastewater. Water Science and Technology, 57, (6), pp Yoochatchaval, W., Ohashi, A., Harada, H., Yamaguchi, T. and Syutsubo K. (2008b). Characteristics of granular sludge in an EGSB reactor for treating low strength wastewater. International Journal of Environmental Research, 2,(4), pp Yoochatchaval, W., Tsushima, I., Yamaguchi, I., Araki, N., Sumino, H., Ohashi, A., Harada, H. and Syutsubo, K. (2009). Influence of sugar content of wastewater on the microbial characteristics of granular sludge developed at 20 C in the anaerobic granular sludge bed reactor. J. of Environmental Science and Health; Part A (Toxic/Hazardous Substance & Environmental Engineering), Vol. 44, ! 9