The Composting Process Control Of Sewage Sludge And Greening Waste In A Rotary Drum Reactor

Composting is an effective method for sewage sludge treatment. To acheave idealcomposting process and product, effective process control strategies are required. Thisstudy mainly focused on the composting of sewage sludge and greening waste(especially wood chips) in a rotary drum reactor. We proposed a process control strategywhich can shorten the processing time, accelerate the degradation of organic mattersand improve the compost quality.The microbial metabolic activity of composting material under differenttemperature shows that: The microbial metabolic activity is the highest whentemperature is around45~50℃. The microbial metabolic activity is significantlyinhibited when the temperature reaches55℃. Thus, we proposed a two-stagetemperature control strategy. The composting process consists of two stages:thermophilic stage (>55℃) and mesophilic stage (45~50℃).The composting processes under different process control strategies wereinvestigated. Results show that: The two-stage temperature control strategy can shortenthe time of composting into less than17days. The two-stage temperature controlstrategy can also accelerate degradation, kill pathogens and reduce nutrient loss.The impact of composted wood chips recirculation on the two-stage temperaturecontrol sewage sludge composting was investigated. The recirculation can improvetemperature conditions and heating rate. When the wood chips recirculation ratio is75%,the temperature reaches55℃in2.5d and the highest temperature is62℃. Therecirculation can reduce water loss and effectively improve the degradation rate duringmesophilic stage. When the wood chips recirculation ratio is75%, the VS degradationrate rises from10.5%to18.8%during mesophilic stage. The recirculation can alsoimprove the degradation of the sewage sludge. When the wood chips recirculation ratiois75%, the proportion of sewage sludge VS degradation rate reaches63.9%.The processes of rotary drum reactor composting and trough composting undertwo-stage temperature control strategy were investigated. Results show that: Duringtrough composting the temperature varies significantly at different positions of thecompost pile. The temperature control is difficult during mesophilic stage. The desiredeffect of two-stage temperature control strategy cannot be achieved during troughcomposting. Furthermore, the degradation characteristics of rotary drum reactor composting and trough composting is completely different: the degradation of VS insewage sludge is greatly affected by material composition, while the total degradation isrelatively irrelevant to material composition. The proportion of sewage sludge VSdegradation rate during thermophilic stage is relatively higher than the mesophilic stage.The two-stage temperature control strategy is not a proper process control strategy fortrough composting.This study proposes an improved process control strategy for sewage sludgecomposting in rotary drum reactor, and provides references for sewage sludge compostmethods selection.