Research On Acid-producing Ability Of Urban Residual Activated Sludge Under Temperature Phased Anaerobic Digestion System

The effects of pH value, temperature, adding ratio of waste activated sludge (WAS) and hydraulic retention time (HRT) on WAS acidification and solubilization in thermophilic anaerobic digestion system and acidification in mesophilic anaerobic digestion system were investigated in the paper. New types of acidification systems were constructed and the main sources of VFAs in the systems were analysised.The release of organic matters in alkaline conditions is superior to acid and neutral conditions. The organics content is at its maximum when pH=11, while excessive alkalinity is bad for the stability of biosystem. The research showed that the optimal pH value is pH=10. The optimum temperature is 60℃, not 50℃or 70℃When the release of organic matters reaches to maximum, the organics content increases with the adding ratio in a certain range.The effects of operating parameters on WAS acidification in thermophilic anaerobic digestion system were investigated, finding that the VFAs accumulation is superior to acid, neutral and excessive alkaline conditions when pH=7. The optimum temperature is 60℃for acidification. The VFAs accumulation would be restrained under lower or higher temperature.The effects of operating parameters on WAS acidification in mesophilic anaerobic digestion system were also investigated, finding that the VFAs accumulation under pH=7 is as good as the pH=11, while the removal rate of organics under pH=7 is higher than pH=11, so the optimal pH value is pH=7. The VFAs content reaches a maximum when adding ratio is 12.5% and HRT is 8d.New types of TPAD systems were constructed:WAS thermophilic-subsequent supernatant thermophilic anaerobic digestion system (TSST) and WAS thermophilic-subsequent supernatant mesophilic anaerobic digestion system (TSSM), and the main sources of VFAs in the systems were analysised, showing that STC/STNb is differ from each other. In the acidification processes, the content of STC, STOC and STIC is decreased due to some soluble organics can be utilized directly and some can be degraded to soluble carbon sources firstly and then be utilized by acid-forming bacteria.