| More attention is paid on anaerobic sequencing batch reactor(ASBR)because of its many advantages such as low investment,flexibility of the operation and the ability of enduring perturbation and so on.However,ASBR is less applied in engineering than the other high efficient reactors such as upflow anaerobic sludge blanket.There are two main reasons.One is that there is pressure fluctuation in the ASBR because of the batch-fed and batch-decanted.The other is the volatile fatty acid accumulation due to the batch operation.In this paper,start-up and granulation in a lab-scale anaerobic sequencing batch reactor fed with a synthetic glucose wastewater were investigated.The accumulation,inhibation and recovery of the volatile fatty acid(VFA)in the ASBR were studied under the condition of the organic load perturbation.Then,brewery wastewater was treated in a pilot-scale anaerobic sequencing batch reactor in which a floating cover was employed.Start-up and granulation in a lab-scale ASBR fed with a synthetic glucose wastewater were investigated.Sludge granulation proceeded after 100 days operation and completed in approximately 120 days,which is much shorter than the granulation time ever reported.Compared with granular sludge formed in other reactors,the one formed in ASBR is smaller in size and denser in compact.Biomass activity can reach as high as 0.22gCOD/VSS.d,0.83gCOD/VSS.d,0.24gCOD/VSS.d and 0.70gCOD/VSS.d for formate,acetate,propionate and butyrate,respectively.The views of SEM showed that filamentous bacteria like Methanosaeta were abundant in the granule and exhibited in a uniform structure.The growth of Methanosaeta can predominate even if high acetate concentration is high in ASBR.Short filamentous bacteria are observed in the effluent.Batch tests showed that composition of these filamentous microorganisms included fermentative,syntrophic acetogenic and methanogenic bacteria,with the ecology similar as that of granular sludge.These results suggest that these filamentous microorganisms are unwinded from the granular.Three glucose-fed anaerobic sequencing batch reactors were used to examine the effect of persistence organic shock loads on reactor performance(accumulation, inhibation and recovery of VFA)and to obtain a greater insight into microbial responses and interactions during the shocks.The reactor was operated at 24-h HRT,5000mgCOD/L influent,and 35±1℃for 175 days as a base-line condition.This resulted in the 92%COD removal efficiency and effluent VFA concentration is less than 200mg/L.The biogas production was kept in steady at 4.8L per cycle.The content of methane in the biogas varied from 60%to 70%. The specific methanogenic activity(SMA)for formate,acetate,propionate and bntyrate was 0.335gCOD/gVSS.d,1.258gCOD/gVSS.d,1.094gCOD/gVSS.d and 0.746g COD/gVSS.d,respectively.After acquiring enough information under base-line condition,two reactors were subjected to a double persistence organic shock loads in which the influent glucose concentration was increased from 5000mgCOD/L to 10000mgCOD/L.5gNaHCO3 was added to keep the pH above to 6.5 in one reactor.The performance of the reactors to the organic shock and the chance of the key intermediates were recorded.A rapid accumulation in glucose fermentation intermediates occurred immediately after initiating the perturbation.Effluent chemical oxygen demand(COD)increased from 185mg/L to a peak level of 2876mg/L in the reactor and carbon dioxide content of the biogas increased from 37%to 52%.The acetate concentration was accumulated to the maximum value at day 3,while the propionate,butyrate and valeric were at day 9, the isobutyrate and the isovalerate was at day 5.The effluent COD concentration was reduced to pre-shock load levels after 17 days operation.The rapid recovery of the system was probable due to the propionate-type fermentation predominant in this system.These observations indicated that the ASBR system was able to adapt to the double persistence organic shock loads.The variation of the acetate,propionate, butyrate and valerate in a cycle during the experiment showed that fermentative, syntrophic acetogenic and methanogenic bacterias were not inhibited when subjected to the shock load.When the system recovered,SMA for formate,acetate,propionate and butyrate was 0.248gCOD/gVSS.d,1.001gCOD/gVSS.d,0.547gCOD/gVSS.d and 0.605gCOD/gVSS.d,respectively.The response of the reactor in which pH value wasn't controlled showed a total difference model.When ASBR was subjected the double organic shock load,effluent COD concentration quickly increased to 8579mg/L on the 4thday,and pH value decreased from 6.61 to 3.32.Not gas was observed.The fermentative,syntrophic acetogenic and methanogenic bacterias were inhibited completely.After adjusting the pH value above 6.0,the system recovered within 179 days.And SMA for formate, acetate,propionate and butyrate was 0.239gCOD/gVSS.d,1.338gCOD/gVSS.d, 1.041gCOD/gVSS.d and 0.926gCOD/gVSS.d,in which SMA for acetate,propionate and butyrate is 1.20,1.32 and 1.24 times of those before shock load.When the system was subjected to the shock load,the methanogenic bacteria was inhibited firstly,then the syntrophic acetogenic bacteria and finally the fermentative bacteria.However,when the system recovered,the fermentative bacteria recovered firstly,then methanogenic bacteria and finally the syntrophic acetogenic bacteria.Treatment of brewery wastewater was investigated in a pilot-scale anaerobic sequencing batch reactor in which a floating cover was employed.Long time experiments showed the reactor worked stably and effectively for both COD removal and gas production.When the organic loading rate was controlled between 1.0kg/m3.d-5.0kg/m3.d,and hydraulic retention time one day,COD removal efficiency could reach more than 90%.Sludge granulation was achieved in the system in approximately 60 days without any chemical addition.SMA for formate,acetate, propionate and butyrate were determined as high as 0.469gCOD/gVSS.d, 0.803gCOD/gVSS.d,0.758gCOD/gVSS.d and 0.710gCOD/gVSS.d respectively. Therefore,ASBR is a potential alternative for brewery wastewater treatment.
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