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Treatment of brewery wastewater using anaerobic sequencing batch reactor (ASBR)
Available online at www.sciencedirect.com
Bioresource Technology 99 (2008) 3182–3186
Treatment of brewery wastewater using anaerobic sequencing batch reactor (ASBR) Shao Xiangwen *, Peng Dangcong, Teng Zhaohua, Ju Xinghua School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China Received 21 March 2007; received in revised form 24 May 2007; accepted 25 May 2007 Available online 30 July 2007
Abstract Brewery wastewater was treated in a pilot-scale anaerobic sequencing batch reactor (ASBR) in which a floating cover@ was employed. Long time experiments showed that the reactor worked stably and effectively for COD removal and gas production. When the organic loading rate was controlled between 1.5 kg COD/m3 d and 5.0 kg COD/m3 d, and hydraulic retention time one day, COD removal efficiency could reach more than 90%. Sludge granulation was achieved in the reactor in approximately 60 days, which is much less than the granulation time ever reported. In addition, high specific methanogenic activity (SMA) for formate was observed. The study suggests that the ASBR technology is a potential alternative for brewery wastewater treatment. 2007 Elsevier Ltd. All rights reserved. Keywords: Brewery wastewater; ASBR; Granular sludge; SMA; Formate
1. Introduction In China, there are more than 100 big breweries in which a great volume of wastewater is produced. For each cubic meter of beer produced, the water consumed in general is 10–20 m3, of which more than 90% will be discharged into sewer system. Moreover, there exists a great amount of beer losses (8.01–14.96%) in production line, which is also entering wastewater collecting system finally (Xu, 2000). Because of the high biodegradability of brewery wastewater (BOD5/ COD > 0.5), biological treatment is widely used. Traditionally, wastewaters from different processes are mixed together and treated with aerobic processes, such as conventional activated sludge, oxidation ditch, sequencing batch reactor and biofilter (Liu, 2003). However, brewery wastewater is characterized by high strength soluble organic pollutants and suspended solids (SS). Aerobic treatment requires an intensive amount of energy for aeration. In addition, a large amount of wasted sludge is *
Corresponding author. Tel.: +86 29 82202506; fax: +86 29 82202729. E-mail address: [email protected] (X. Shao).
0960-8524/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.05.050
produced, which costs large capital to disposal. Therefore, Brewery companies are reluctant to employ wastewater treatment facilities. Source separation is an alternative for sustainable solution. For the part of wastewaters discharged from boiling and fermentation processes in which high strength organic carbon is contained, anaerobic treatment is believed to be the best choice. High rate anaerobic reactors, such as up-flow anaerobic blanket reactor (UASB), anaerobic granular bed baffled reactor (GRABBR) and anaerobic fluidized bed (AFB), have been reported to treat brewery wastewater and a satisfactory COD reduction obtained (Baloch et al., 2007; Ochieng et al., 2002; Parawira et al., 2005). Anaerobic sequencing batch reactor (ASBR) is a newly developed technology and has been extensively studied due to its advantages: (1) no short circuit, as in the case of fixed-bed continuous systems; (2) high efficiency for both COD removal and gas production; (3) no primary and secondary settles; (4) flexible control, etc. This new technology has been successfully applied in laboratory and pilot scales for treatment of high strength wastewaters, such as landfill leachate (Bodı´k et al., 2002; Hollopeter and Dague, 1994;
X. Shao et al. / Bioresource Technology 99 (2008) 3182–3186
¨ zturk, 1999), Kennedy and Lentz, 2000; Timur and O slaughterhouse wastewater, municipal sludge (Zhang et al., 1996) and dairy wastewater (Dugba and Zhang, 1999). However, no study has been reported for brewery wastewater treatment. In this study, brewery wastewater was treated using a pilot-scale ASBR reactor with floating cover@ (patent no: ZL 2004 2 0042282.3). The performance of the reactor, such as COD removal, gas production, sludge granulation and specific methanogenic activities (SMA), is investigated. 2. Methods 2.1. ASBR reactor The pilot-scale ASBR used in this work was made of PVC (33 cm in diameter and 120 cm in height) with a working volume of 45 L. A stirrer with 150 RPM was restored to provide the mixing of substrate and biomass in the reactor. Gas production was recorded with a wet gas meter continuously. The temperature in the reactor was controlled at 33 ± 1 C.
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2.5. Analytical methods COD, pH, suspended solids (SS), alkalinity, mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) were analyzed according to the standard methods. The volatile fatty acids (VFA) were measured using a gas chromatograph (THERMO-FINNGAN GC2000) equipped with a capillary column (DBFFAP, 0.32 mm · 30 m) and flame ionization detector (FID). Injector and detector temperatures were 230 and 250 C, respectively. The temperature of the oven was programmed to rise from 100 to 200 C during the analysis with an elevation of 10 C/min. Nitrogen gas (flow rate: 1.0 mL/min) was used as a carrier. The sludge specific methanogenic activities (SMAs) for formate, acetate, propionate and butyrate were determined at 35 C using serum bottles test (280 mL) with 250 mL basal medium supplemented with 2–4 gVSS/L sludge taken from the reactor and 1.2 g COD/L of formate, acetate, propionate and butyrate respectively.
3. Results and discussion 2.2. Seed sludge 3.1. Chemical oxygen demand removal
The wastewater discharged from the boiling and fermentation process is approximately 5000 mg COD/L, which is composed of concentrated water from the boiling vessel and washing water. The concentrated wastewater was obtained from Xi’an Hansi Brewaryhouse with a chemical oxygen demand (COD) of 22 500–32 500 mg/L, TKN of 320–450 mg/L, TP of 144–216 mg/L, volatile suspended solids (VSS) of 1400–4800 mg/L, and pH of 3.2–3.9, and was diluted to required strength with potable water as that discharged before feeding. NaHCO3 was added to adjust the influent pH in the range of 6–7.
The ASBR was started with an organic loading rate (OLR) of 1.0 kg COD/m3 d, then the organic loading rate increased step by step to guarantee a low COD effluent. The batch cycle was controlled in 8 h during which 1 h was used for feeding, 6.35 h for reacting, 0.5 h for settling and 0.15 h for decanting. Fifteen liters of supernatant water was decanted per cycle, which provided a hydraulic retention time (HRT) of 24 h. When COD in the effluent was kept in stable, samples were obtained to evaluate the reactor performance.
COD(mg/L)
2.4. ASBR operation
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2.3. Brewery wastewater
The experiment lasted for 250 days. The time courses of COD in influent and effluent and organic loading rate (OLR) are shown in Fig. 1. It can be seen that the reactor worked very well. During start-up period, COD concentration in the effluent was kept in less than 300 mg/L even OLR was increased quickly to 3.0 kg COD/m3 d. Correspondingly, COD removal efficiency was more than 90%, and significant gas production was observed. On the 53rd day, OLR in the reactor reached to 5.0 kg COD/m3 d and COD removal efficiency maintained in the same level. Although there was significant fluctuation on organic loading rate in the following experiment, the COD removal efficiency stabilized and a very low effluent COD was obtained. Compared with other reactors treating the same type of wastewater, OLR in ASBR was relatively low. Baloch et al. (2007) obtained an OLR of 2.16–13.38 kg COD/m3 d and a COD removal of 93–96% in a GRABBR reactor. Parawira
OLR(kgCOD/m d)
The seed sludge was taken from a UASB reactor in Xi’an Hans Breweryhouse. The sludge is typically flocculent with MLSS of 22.510 g/L, MLVSS of 8.398 g/L and VSS/SS of 0.37. Thirty liters of the sludge was pumped into the reactor.
1 250
OLR
Fig. 1. Variation of CODinf, CODeff and volume loading rate (OLR) during the experiment.
et al. (2005) reported an OLR of 6.0 kg COD/m3 d and a COD removal of 60% in a UASB reactor. Low OLR was due to batch operation in ASBR. Low effluent COD was also expected to meet the local strict discharge permission. In this study, soluble COD in the effluent was normally less than 150 mg/L.
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3.2. Volatile fatty acid profile
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High VFA was contained in brewery wastewater, which resulted in it very acidic (pH in the range of 3–4). Before feeding, Soda ash was added to adjust pH to 6–7 to guarantee the biomethane process to take place smoothly. Variations of VFA in influent and effluent during the experiment are shown in Fig. 2. VFA in the effluent was very low (below 200 mg/L in most cases) even though there was a significant fluctuation in the feed (between 300 and 1500 mg/L as HAc). Thus, the experiment showed that VFA in the feed could be utilized effectively by methanogenesis bacteria. High VFA concentration in the feed didnot affect the one in the effluent. 3.3. Gas production and composition Biogas production was measured daily. The variations of biogas production during the experiment are shown in Fig. 3. The biogas production was low at the beginning of the experiment due to low OLR and then increased along with the increase of OLR. On the 217th day, OLR was raised to 5.0 kg COD/m3 d and the gas production reached as high as 2.40 L/L d, equivalent to 0.48 m3/ kg COD removed. The average methane composition in the gas was 68% during the experiment. 1600 VFA(mg/L)
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Accumulation gas production(L)
X. Shao et al. / Bioresource Technology 99 (2008) 3182–3186
COD and VFA(mg/L)
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Fig. 4. Profiles of COD, VFA and accumulation gas production in a cycle.
3.4. The profile of COD, VFA and gas production in a cycle Fig. 4 shows the profiles of COD, VFA, and biogas production in a typical cycle (5000 mg COD/L in the influent on the 56th day). VFA is an intermediate and indicator in the anaerobic process. Since acid producing bacteria grow more quickly than acid consuming bacteria on readily biodegradable organics such as brewery wastewater, batch operation will provoke accumulation of these acids, mainly at the beginning of a cycle, which may lead to pH reduction and, consequently, methanogenesis inhibition. Therefore, it is the critical to balance the VFA production and utilization in order to keep a low VFA concentration in a cycle. COD concentration reached the highest value at the end of the feed, then decreased linearly along with operation time. For VFA, it stabilized approximately 2 h in its highest value, then declined to the lowest. Profile of COD and VFA in the reactor showed that species involving in anaerobic process interact and equilibrate well. Gas production accorded well with the change of COD and VFA. Gas production rate in a cycle was nearly the same (3.29 L/h). Therefore, a linear accumulate gas production line was observed in Fig. 4.
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3.5. Characteristics of sludge 800 400 0 0
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Fig. 2. Variation of VFAinf, VFAeff during the experiment.
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Fig. 3. Variation of gas production with OLR during the experiment.
The inoculum in this study was flocculent. After two months cultivation, the sludge in the reactor was completely granulized. The average diameter of granules was approximately 0.5 mm and SVI was 28.88 mL/g. Compared with granular sludge developed in UASB, the granule in ASBR is smaller in size and greater in density. The time of granulation in this work is much shorter than that reported by Sung and Dague (1995). They observed granulation of the biomass after ten months operation in a nonfat dry milk fed ASBR. The rapid sludge granulation may be contributed to the wastewater composition and reactor configuration. The main constitute of the wastewater from boiling process of brewery Plant is carbohydrate, which is suggested to benefit granular sludge formation in UASB and ABR (Hulshoff, 2004). Floating cover used in this study can balance effectively the fluctuation of pressure in ASBR during feeding and withdrawing and stimulate sludge granulation in the reactor. This result suggested that
X. Shao et al. / Bioresource Technology 99 (2008) 3182–3186
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Fig. 5. Changes of MLVSS, MLSS and MLVSS/MLSS in the reactor during the experiment.
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acetate
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Fig. 6. Maximum specific methanogenic activities (SMA).
treatment has so high SMA for formate needs more study. Characteristics of the feed, reactor configuration may be some possible reasons. 4. Conclusion ASBR is highly effective for COD removal for high strength wastewater from brewery production plant. When the organic loading rate is operated between 1.5 kg COD/ m3 d and 5.0 kg COD/m3 d, and hydraulic retention time one day, COD removal efficiency can reach more than 90% even though VFA in the feed was fluctuating from 300 mg/L to 1500 mg/L. Besides COD reduction, the process has the potential to produce energy. The gas production reached as high as 2.40 L/L d. Methane composition varied between 50% and 80%. Granulation can be achieved in ASBR in approximately 60 days. The granular sludge formed in the reactor has a very good settling ability and biomass activity, 0.947 g COD/g VSS d, 0.786 g COD/ g VSS d, 0.674 g COD/g VSS d and 0.624 g COD/g VSS d for formate, acetate, propionate and butyrate, respectively. Therefore, ASBR is a potential alternative for brewery wastewater treatment. Acknowledgement This research is partly supported by a grant from National Natural Science Foundation of China (NSFC). Grant No. 50478047. References
MLVSS/MLSS(%)
MLVSS,MLVSS (g/L)
ASBR configuration is suitable for brewery wastewater treatment. Changes of sludge concentration in the reactor with operation time are shown in Fig. 5. The MLVSS and MLVSS in the seeding sludge were 8.40 g/L and 22.51 g/L and decreased to 4.57 g/L and 16.58 g/L on the 50th day due to washout of the poor settling biomass. Afterwards, MLVSS and MLSS in the reactor increased gradually, and VSS/SS rose to 90.8% at the end of the experiment. The SMAs for formate, acetate, propionate and butyrate were determined to evaluate the reactor performance. SMA for the seeding sludge is very low (0.177 g COD/ g VSS d, 0.108 g COD/g VSS, 0.082 g COD/g VSS d and 0.092 g COD/g VSS d for formate, acetate, propionate and butyrate, respectively). After 60 days operation, sludge in the reactor was completely granulized and SMAs increased to 0.297 g COD/g VSS d, 0.721 g COD/g VSS d, 0.436 g COD/g VSS d and 0.664 g COD/g VSS d, respectively (Fig. 6). High SMA owed clearly to sludge granulation. High formate activity was observed in the study. At the beginning, SMA for formate was 0.177 g COD/g VSS d. However, it reached as high as 0.947 g COD/g VSS d at the end of the experiment. Although acetogenesis of butyrate and propionate through pathway of formate formation was suggested by Stams and Dong (1995) and Frank et al. (2002), high SMA for formate was observed only in pure culture. Why the biomass formed in brewery wastewater
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Baloch, M.I., Akunna, J.C., Collier, P.J., 2007. The performance of a phase separated granular bed bioreactor treating brewery wastewater. Bioresour. Technol. 98 (9), 1849–1855. Bodı´k, I., Herdova´, B., Drtil, M., 2002. The use of upflow anaerobic filter and AnSBR for wastewater treatment at ambient temperature. Water Res. 36 (4), 1084–1088. Dugba, P.N., Zhang, R., 1999. Treatment of dairy wastewater with two stage anaerobic sequencing batch reactor systems: thermophic versus mesophilic operations. Bioresour. Technol. 68, 225–233. Frank, A.M., Maurice, L.G., Alfons, J.M., 2002. Biochemical evidence for formate transfer in syntrophic propionate-oxidizing cocultures of syntrophobacter fumaroxidans and Methanospirillum hungatei. Appl. Environ. Microb. 68 (9), 4247–4252. Hollopeter, J.A., Dague, R.R., 1994. Anaerobic sequencing batch reactor treatment of landfill leachate. In: 49th Purdue Industrial Waste Conference Proceedings. Ann Arbor Press, Chelsea, Mich, pp. 277– 284. Hulshoff, P.L.W., 2004. Anaerobic sludge granulation. Water Res. 38 (6), 1376–1389. Kennedy, K.J., Lentz, E.M., 2000. Treatment of landfill leachate using sequencing batch and continuous flow upflow anaerobic sludge blanket (UASB) reactors. Water Res. 34 (14), 3640–3656. Liu, Y., 2003. On the techniques of biochemical processing of brewery wastewater and the prospect. J. Hefei Univ. Tech. 26 (1), 145–149. Ochieng, A.A., Ogadab, T., Sisenda, W.C., Wambua, P., 2002. Brewery wastewater treatment in a fluidised bed bioreactor. J. Hazard. Mater. B (90), 311–321. Parawira, W.I., Kudita, M.G., Nyandoroh, R., Zvauya, A., 2005. A study of industrial anaerobic treatment of opaque beer brewery wastewater
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in a tropical climate using a full-scale UASB reactor seeded with activated sludge. Proc. Biochem. 40, 593–599. Stams, A.J., Dong, X., 1995. Role of formate and hydrogen in the degradation of propionate and butyrate by defined suspended cocultures of acetogenic and methanogenic bacteria. Antonie Van Leeuwenhoek 68 (4), 281–284. Sung, W., Dague, R., 1995. Laboratory studies on the anaerobic sequencing batch reactor. Water Environ. Res. 67 (3), 294–301.
¨ zturk, I., 1999. Anaerobic sequencing batch reactor Timur, H., O treatment of landfill leachate. Water Res. 33 (15), 3225–3230. Xu, H., 2000. The development trend of treatment technology for brewery wastewater. Sichuan Environ. 22 (3), 27–32. Zhang, R., Yin, Y., Sung, S., Dague, R., 1996. Anaerobic treatment of swine waste by the anaerobic sequencing batch reactor. In: 51th Purdue Industrial Waste Conference Proceedings.
Bioresource Technology 99 (2008) 3182–3186
Treatment of brewery wastewater using anaerobic sequencing batch reactor (ASBR) Shao Xiangwen *, Peng Dangcong, Teng Zhaohua, Ju Xinghua School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China Received 21 March 2007; received in revised form 24 May 2007; accepted 25 May 2007 Available online 30 July 2007
Abstract Brewery wastewater was treated in a pilot-scale anaerobic sequencing batch reactor (ASBR) in which a floating cover@ was employed. Long time experiments showed that the reactor worked stably and effectively for COD removal and gas production. When the organic loading rate was controlled between 1.5 kg COD/m3 d and 5.0 kg COD/m3 d, and hydraulic retention time one day, COD removal efficiency could reach more than 90%. Sludge granulation was achieved in the reactor in approximately 60 days, which is much less than the granulation time ever reported. In addition, high specific methanogenic activity (SMA) for formate was observed. The study suggests that the ASBR technology is a potential alternative for brewery wastewater treatment. 2007 Elsevier Ltd. All rights reserved. Keywords: Brewery wastewater; ASBR; Granular sludge; SMA; Formate
1. Introduction In China, there are more than 100 big breweries in which a great volume of wastewater is produced. For each cubic meter of beer produced, the water consumed in general is 10–20 m3, of which more than 90% will be discharged into sewer system. Moreover, there exists a great amount of beer losses (8.01–14.96%) in production line, which is also entering wastewater collecting system finally (Xu, 2000). Because of the high biodegradability of brewery wastewater (BOD5/ COD > 0.5), biological treatment is widely used. Traditionally, wastewaters from different processes are mixed together and treated with aerobic processes, such as conventional activated sludge, oxidation ditch, sequencing batch reactor and biofilter (Liu, 2003). However, brewery wastewater is characterized by high strength soluble organic pollutants and suspended solids (SS). Aerobic treatment requires an intensive amount of energy for aeration. In addition, a large amount of wasted sludge is *
Corresponding author. Tel.: +86 29 82202506; fax: +86 29 82202729. E-mail address: [email protected] (X. Shao).
0960-8524/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.05.050
produced, which costs large capital to disposal. Therefore, Brewery companies are reluctant to employ wastewater treatment facilities. Source separation is an alternative for sustainable solution. For the part of wastewaters discharged from boiling and fermentation processes in which high strength organic carbon is contained, anaerobic treatment is believed to be the best choice. High rate anaerobic reactors, such as up-flow anaerobic blanket reactor (UASB), anaerobic granular bed baffled reactor (GRABBR) and anaerobic fluidized bed (AFB), have been reported to treat brewery wastewater and a satisfactory COD reduction obtained (Baloch et al., 2007; Ochieng et al., 2002; Parawira et al., 2005). Anaerobic sequencing batch reactor (ASBR) is a newly developed technology and has been extensively studied due to its advantages: (1) no short circuit, as in the case of fixed-bed continuous systems; (2) high efficiency for both COD removal and gas production; (3) no primary and secondary settles; (4) flexible control, etc. This new technology has been successfully applied in laboratory and pilot scales for treatment of high strength wastewaters, such as landfill leachate (Bodı´k et al., 2002; Hollopeter and Dague, 1994;
X. Shao et al. / Bioresource Technology 99 (2008) 3182–3186
¨ zturk, 1999), Kennedy and Lentz, 2000; Timur and O slaughterhouse wastewater, municipal sludge (Zhang et al., 1996) and dairy wastewater (Dugba and Zhang, 1999). However, no study has been reported for brewery wastewater treatment. In this study, brewery wastewater was treated using a pilot-scale ASBR reactor with floating cover@ (patent no: ZL 2004 2 0042282.3). The performance of the reactor, such as COD removal, gas production, sludge granulation and specific methanogenic activities (SMA), is investigated. 2. Methods 2.1. ASBR reactor The pilot-scale ASBR used in this work was made of PVC (33 cm in diameter and 120 cm in height) with a working volume of 45 L. A stirrer with 150 RPM was restored to provide the mixing of substrate and biomass in the reactor. Gas production was recorded with a wet gas meter continuously. The temperature in the reactor was controlled at 33 ± 1 C.
3183
2.5. Analytical methods COD, pH, suspended solids (SS), alkalinity, mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) were analyzed according to the standard methods. The volatile fatty acids (VFA) were measured using a gas chromatograph (THERMO-FINNGAN GC2000) equipped with a capillary column (DBFFAP, 0.32 mm · 30 m) and flame ionization detector (FID). Injector and detector temperatures were 230 and 250 C, respectively. The temperature of the oven was programmed to rise from 100 to 200 C during the analysis with an elevation of 10 C/min. Nitrogen gas (flow rate: 1.0 mL/min) was used as a carrier. The sludge specific methanogenic activities (SMAs) for formate, acetate, propionate and butyrate were determined at 35 C using serum bottles test (280 mL) with 250 mL basal medium supplemented with 2–4 gVSS/L sludge taken from the reactor and 1.2 g COD/L of formate, acetate, propionate and butyrate respectively.
3. Results and discussion 2.2. Seed sludge 3.1. Chemical oxygen demand removal
The wastewater discharged from the boiling and fermentation process is approximately 5000 mg COD/L, which is composed of concentrated water from the boiling vessel and washing water. The concentrated wastewater was obtained from Xi’an Hansi Brewaryhouse with a chemical oxygen demand (COD) of 22 500–32 500 mg/L, TKN of 320–450 mg/L, TP of 144–216 mg/L, volatile suspended solids (VSS) of 1400–4800 mg/L, and pH of 3.2–3.9, and was diluted to required strength with potable water as that discharged before feeding. NaHCO3 was added to adjust the influent pH in the range of 6–7.
The ASBR was started with an organic loading rate (OLR) of 1.0 kg COD/m3 d, then the organic loading rate increased step by step to guarantee a low COD effluent. The batch cycle was controlled in 8 h during which 1 h was used for feeding, 6.35 h for reacting, 0.5 h for settling and 0.15 h for decanting. Fifteen liters of supernatant water was decanted per cycle, which provided a hydraulic retention time (HRT) of 24 h. When COD in the effluent was kept in stable, samples were obtained to evaluate the reactor performance.
COD(mg/L)
2.4. ASBR operation
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2.3. Brewery wastewater
The experiment lasted for 250 days. The time courses of COD in influent and effluent and organic loading rate (OLR) are shown in Fig. 1. It can be seen that the reactor worked very well. During start-up period, COD concentration in the effluent was kept in less than 300 mg/L even OLR was increased quickly to 3.0 kg COD/m3 d. Correspondingly, COD removal efficiency was more than 90%, and significant gas production was observed. On the 53rd day, OLR in the reactor reached to 5.0 kg COD/m3 d and COD removal efficiency maintained in the same level. Although there was significant fluctuation on organic loading rate in the following experiment, the COD removal efficiency stabilized and a very low effluent COD was obtained. Compared with other reactors treating the same type of wastewater, OLR in ASBR was relatively low. Baloch et al. (2007) obtained an OLR of 2.16–13.38 kg COD/m3 d and a COD removal of 93–96% in a GRABBR reactor. Parawira
OLR(kgCOD/m d)
The seed sludge was taken from a UASB reactor in Xi’an Hans Breweryhouse. The sludge is typically flocculent with MLSS of 22.510 g/L, MLVSS of 8.398 g/L and VSS/SS of 0.37. Thirty liters of the sludge was pumped into the reactor.
1 250
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Fig. 1. Variation of CODinf, CODeff and volume loading rate (OLR) during the experiment.
et al. (2005) reported an OLR of 6.0 kg COD/m3 d and a COD removal of 60% in a UASB reactor. Low OLR was due to batch operation in ASBR. Low effluent COD was also expected to meet the local strict discharge permission. In this study, soluble COD in the effluent was normally less than 150 mg/L.
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High VFA was contained in brewery wastewater, which resulted in it very acidic (pH in the range of 3–4). Before feeding, Soda ash was added to adjust pH to 6–7 to guarantee the biomethane process to take place smoothly. Variations of VFA in influent and effluent during the experiment are shown in Fig. 2. VFA in the effluent was very low (below 200 mg/L in most cases) even though there was a significant fluctuation in the feed (between 300 and 1500 mg/L as HAc). Thus, the experiment showed that VFA in the feed could be utilized effectively by methanogenesis bacteria. High VFA concentration in the feed didnot affect the one in the effluent. 3.3. Gas production and composition Biogas production was measured daily. The variations of biogas production during the experiment are shown in Fig. 3. The biogas production was low at the beginning of the experiment due to low OLR and then increased along with the increase of OLR. On the 217th day, OLR was raised to 5.0 kg COD/m3 d and the gas production reached as high as 2.40 L/L d, equivalent to 0.48 m3/ kg COD removed. The average methane composition in the gas was 68% during the experiment. 1600 VFA(mg/L)
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X. Shao et al. / Bioresource Technology 99 (2008) 3182–3186
COD and VFA(mg/L)
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1
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Fig. 4. Profiles of COD, VFA and accumulation gas production in a cycle.
3.4. The profile of COD, VFA and gas production in a cycle Fig. 4 shows the profiles of COD, VFA, and biogas production in a typical cycle (5000 mg COD/L in the influent on the 56th day). VFA is an intermediate and indicator in the anaerobic process. Since acid producing bacteria grow more quickly than acid consuming bacteria on readily biodegradable organics such as brewery wastewater, batch operation will provoke accumulation of these acids, mainly at the beginning of a cycle, which may lead to pH reduction and, consequently, methanogenesis inhibition. Therefore, it is the critical to balance the VFA production and utilization in order to keep a low VFA concentration in a cycle. COD concentration reached the highest value at the end of the feed, then decreased linearly along with operation time. For VFA, it stabilized approximately 2 h in its highest value, then declined to the lowest. Profile of COD and VFA in the reactor showed that species involving in anaerobic process interact and equilibrate well. Gas production accorded well with the change of COD and VFA. Gas production rate in a cycle was nearly the same (3.29 L/h). Therefore, a linear accumulate gas production line was observed in Fig. 4.
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3.5. Characteristics of sludge 800 400 0 0
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Fig. 2. Variation of VFAinf, VFAeff during the experiment.
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Fig. 3. Variation of gas production with OLR during the experiment.
The inoculum in this study was flocculent. After two months cultivation, the sludge in the reactor was completely granulized. The average diameter of granules was approximately 0.5 mm and SVI was 28.88 mL/g. Compared with granular sludge developed in UASB, the granule in ASBR is smaller in size and greater in density. The time of granulation in this work is much shorter than that reported by Sung and Dague (1995). They observed granulation of the biomass after ten months operation in a nonfat dry milk fed ASBR. The rapid sludge granulation may be contributed to the wastewater composition and reactor configuration. The main constitute of the wastewater from boiling process of brewery Plant is carbohydrate, which is suggested to benefit granular sludge formation in UASB and ABR (Hulshoff, 2004). Floating cover used in this study can balance effectively the fluctuation of pressure in ASBR during feeding and withdrawing and stimulate sludge granulation in the reactor. This result suggested that
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Fig. 5. Changes of MLVSS, MLSS and MLVSS/MLSS in the reactor during the experiment.
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Fig. 6. Maximum specific methanogenic activities (SMA).
treatment has so high SMA for formate needs more study. Characteristics of the feed, reactor configuration may be some possible reasons. 4. Conclusion ASBR is highly effective for COD removal for high strength wastewater from brewery production plant. When the organic loading rate is operated between 1.5 kg COD/ m3 d and 5.0 kg COD/m3 d, and hydraulic retention time one day, COD removal efficiency can reach more than 90% even though VFA in the feed was fluctuating from 300 mg/L to 1500 mg/L. Besides COD reduction, the process has the potential to produce energy. The gas production reached as high as 2.40 L/L d. Methane composition varied between 50% and 80%. Granulation can be achieved in ASBR in approximately 60 days. The granular sludge formed in the reactor has a very good settling ability and biomass activity, 0.947 g COD/g VSS d, 0.786 g COD/ g VSS d, 0.674 g COD/g VSS d and 0.624 g COD/g VSS d for formate, acetate, propionate and butyrate, respectively. Therefore, ASBR is a potential alternative for brewery wastewater treatment. Acknowledgement This research is partly supported by a grant from National Natural Science Foundation of China (NSFC). Grant No. 50478047. References
MLVSS/MLSS(%)
MLVSS,MLVSS (g/L)
ASBR configuration is suitable for brewery wastewater treatment. Changes of sludge concentration in the reactor with operation time are shown in Fig. 5. The MLVSS and MLVSS in the seeding sludge were 8.40 g/L and 22.51 g/L and decreased to 4.57 g/L and 16.58 g/L on the 50th day due to washout of the poor settling biomass. Afterwards, MLVSS and MLSS in the reactor increased gradually, and VSS/SS rose to 90.8% at the end of the experiment. The SMAs for formate, acetate, propionate and butyrate were determined to evaluate the reactor performance. SMA for the seeding sludge is very low (0.177 g COD/ g VSS d, 0.108 g COD/g VSS, 0.082 g COD/g VSS d and 0.092 g COD/g VSS d for formate, acetate, propionate and butyrate, respectively). After 60 days operation, sludge in the reactor was completely granulized and SMAs increased to 0.297 g COD/g VSS d, 0.721 g COD/g VSS d, 0.436 g COD/g VSS d and 0.664 g COD/g VSS d, respectively (Fig. 6). High SMA owed clearly to sludge granulation. High formate activity was observed in the study. At the beginning, SMA for formate was 0.177 g COD/g VSS d. However, it reached as high as 0.947 g COD/g VSS d at the end of the experiment. Although acetogenesis of butyrate and propionate through pathway of formate formation was suggested by Stams and Dong (1995) and Frank et al. (2002), high SMA for formate was observed only in pure culture. Why the biomass formed in brewery wastewater
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