Study On The Key Issues Of The Anaerobic Digestion Of Municipal Waste Activated Sludge(WAS)

The research object of this thesis was municipal waste activated sludge(WAS), aiming at the problem of low efficiency of hydrolysis rate and imbalance of C/N ratio in anaerobic digestion(AD) of WAS. Biological and physical pretreatment were applied to enhance the hydrolysis of organic matters in WAS. The C/N ratio was optimized and high quality inoculum was used to improve the conversion efficiency of organic matters. Furthermore, the environmental risk of digested sludge was evaluated in terms of heavy metals and pathogen. The thesis aimed to provide theoretical support for the WAS treatment and disposal. Some main results of the present research are obtained as following:The hydrolysis efficiency could be enhanced by involving inoculums during hydrolysis test in facultative conditions. It demonstrated that the VFAs and NH4+-N of raw sludge with inoculum increased by as much as 965.3 mg/L and 635.6 mg/L, respectively, while that of the sterilized sludge with inoculum increased by as much as 2104.1 mg/L and 700.6 mg/L, respectively. The specific biogas production of WAS enhanced by 20.5% with oleic acid acclimated inoculum. Soluble substance and cumulative biogas production in AD increased after high pressure homogenization(HPH) and ultrasonic pretreatment. DDCOD was 5.4% and 2%, and the biogas yield in 20 d increased by 507.0% and 18.5% after HPH and ultrasonic pretreatment, respectively.Spent mushroom substrate(SMS) could be used as supplementary carbon source for WAS. By adding Plelmtus eqngiu SMS to sonicated WAS, the biogas production from WAS and Volatile Solid Reduction(VSR) increased by 20.9% and 17.7%, respectively.Ni and Cd should be regarded as the priority pollutants for elimination according to the contents of total, stable state and mobile state of metals. No remarkable changes of metal speciation were observed during 21-day mesophilic AD. Pb and Hg mainly associated with stable state, while Ni, Cu, Cr and As dominated in unstable state. The leaching concentrations of all selected heavy metals were less than 1%, indicating that the sludge does not pose leaching toxicity risk.After 21-day mesophilic AD, the bacterial colony number was reduced by 88.8%~94.7%. Both total coliforms and faecal coliforms were reduced by 99%, and salmonella spp. was not detected.