Sludge Fermentation And Volatile Fatty Acids Accumulation In Anaerobic Sequencing Batch Reactor

With the rapid development of wastewater treatment plants (WWTPs), resulting in a huge amount of sewage sludge, how to deal with the sludge has become a common concern around the world. Since the1980s, a number of research have been conducted by domestic and foreign scholars to investigate on the anaerobic fermentation of sludge. The evidence shows that acid fermentation is a available method for treating sludge as it can stabilize sludge, kill pathogens, reduce solids, and produce large amounts of volatile fatty acids (VFAs), including acetic, propionic, iso-butyric, butyric, iso-valeric, and valeric acids and so on. The volatile fatty acids (VFAs), existing in dissolved form, can be used as supplemental carbon sources, which resolves the current problem of insufficient carbon source during the removal of nitrogen and phosphorus in the sewage treatment. The anaerobic sequencing batch reactor (ASBR) process, which achieved the separation of the SRT and HRT, is believed to be a promising process for treating sludge, because it can maintain a high concentration of bacteria and treat high-solids waste streams with high-rate system.Anaerobic sequencing batch reactor was be used to treat sludge which from the dewater room in municipal wastewater treatment plant located in Taiyuan. Effects of interval time of discharging sludge on sludge fermentation and volatile fatty acids accumulation in ASBR operated at room temperature were evaluated in this paper. In addition, effects of HRT on the acid yield from sludge fermentation under the optimal interval time of discharging sludge were also investigated. Results obtained are as follows:1. In the condition of temperature of20±1℃, the feed VS concentration of15g/L, the effective HRT of6.0day, HCl to adjust pH of6.0, the best acidogenic effects in ASBR was achieved at2day interval time of discharging sludge. In this batch test, the maximum average acid yield from sludge fermentation was145mgVFAs/gVS.2. In the condition of temperature of20±1℃, the feed VS concentration of15g/L, the effective HRT of4.0day, HCl to adjust pH of6.0, the best acidogenic effects in ASBR was achieved at2day interval time of discharging sludge. In this batch test, the maximum average acid yield from sludge fermentation was64mgVFAs/gVS.3. In the condition of temperature of20±1℃, the feed VS concentration of15g/L, the effective HRT of3.0day, HCl to adjust pH of6.0, the best acidogenic effects in ASBR was achieved at2day interval time of discharging sludge. In this batch test, the maximum average acid yield from sludge fermentation was116mgVFAs/gVS.4. Interval time of discharging sludge which have an important impact on ASBR system of sludge acid fermentation, can be used as the parameter to control the operating of system. The effects of interval time of discharging sludge on system was associated with the SRT and HRT, and no matter under what conditions of HRT, the best interval time exists and is unique.5. Considering the running stability and the acidogenic effects of system, in the condition of temperature of20±1℃, the feed VS concentration of15g/L, the HCl to adjust pH of6.0,2day can be chose as the best interval time of discharging sludge for ASBR system to treatment sludge.6. In the condition of temperature of20±1℃, the feed VS concentration of15g/L, the interval time of discharging sludge of2day, HCl to adjust pH of6.0, the better acidogenic effect in ASBR was achieved at6.0day of the effective HRT. When the effective HRT was6.0day and4.0day, their average acid yield from sludge fermentation was81and60mgVFAs/gVS, respectively. In other words, the longer the HRT, the better the acidogenic effects.7. Considering the running stability, the acidogenic effects and the degradation rate of TS and VS of system, the optimum conditions of ASBR for treatment of sewage sludge were established. The conditions were listed as follows:temperature of20±1℃, the feed VS concentration of15g/L, the HCl to adjust pH of6.0, the effective HRT of6.0day, interval time of discharging sludge of2day.