The Study On The Characteristics Of The Anaerobic Co-digestion Of Waste Activated Sludge And Food Waste

As one by-product produced by sewage treatment, the yield of the waste activated sludge(WAS) increased rapidly with the improvement of wastewater treatment ratio, resulting in thegrowing threat for the protection of urban environment. Anaerobic digestion (AD), as onekind of treatment methods for excess sludge, not only realize reduction and harmless, but alsogenerate clean energy-biogas, further achieve resource compared with composting,incineration and landfill. In order to solve the drawback of the relatively low energyproduction efficiency of conventional anaerobic digestion for sludge, food waste (FW), whichwith high organic content, was added into the reactor to balance the nutrients constitute,finally improving the performance of anaerobic digestion system. The continuously stirredtank reactors (CSTR) were used in this research to study the performance of anaerobicco-digestion of WAS and FW. The whole experiment was divided into the two stages, whichincluded the investigation of the best mixing ratio and effects of organic loading rate (OLR)on the performance of anaerobic co-digestion under different temperatures.In the first stage, starting up the reactor under high temperature (55℃) withsemi-continuous feeding to study the effects of the mixing ratio on the performance andstability of anaerobic co-digestion system. Results showed that the acid yields of experimentalgroups which added food waste were increased rapidly during the first several days, but cangradually achieve a steady state through adjusting alkalinity and pH by NaHCO3, and theenergy production efficiencies were also considerably higher than than that of pure sludgeanaerobic system. When the WAS and FW were mixed with a total solids (TS) ratio of1:0.5,the methane yield was600mL/d, and the VS removal rate reached around60%, and thismixing ratio was the optimum condition from the perspective of efficiency and systemstability.In the second stage, starting up the anaerobic co-digestion systems with the same OLR of1g VS/L/d and TS ratio of1:0.5at35,45and55℃, respectively, gradually increased organicloading rate (1~8g VS/L/d) in188days to investigate the variation of the performance ofco-digsrtion system. Results show that the GPR at55℃was1.6and1.3times higher thanthat at35and45℃with the OLR of1g/VS/L, and the corresponding average CH4yieldswere0.40,0.26and0.30LCH4/g VSadded, respectively. During the stabilization period, the gasproduction rate of each system is gradually increased with the increasing organic loading rate,while the methane yield and VS removal decreased. The thermophilic system exhibited the best load bearing capacity at extremely high OLR of7g VS/L/d, while the mesophilic systemshowed the best process stability at low OLRs (<5g VS/L/d). Further studies of microbialcommunities for each system by means of PCR-DGGE showed that temperature had a moreremarkable effect on the richness and diversity of microbial populations than the OLR.