[Start-up of a thermophilic anaerobic sludge digester]

Anaerobic digestion is one of the most widely-used technologies of the sludge reduction and stabilization, in which thermophilic digestion has advantage of fast stabilization. But it is lack of operation experience in China. Thus start-up of a thermophilic anaerobic sludge digester treating excess activated sludge was investigated. The digester was an internal circulation anaerobic sludge digester. It belongs to upflow reactor and its hydrodynamic conditions can be controlled by backflow biogas. A multistep strategy was applied to the start-up to enhance anaerobic bacteria to adapt the changes of temperature, reactor and treated sludge, including: to feed the digester with easily-degraded glucose to enhance bacteria reproduce at the first beginning with COD organic loading of 2.4 kg/(m3 x d); to accelerate the internal circulation; to control pH within a optimal range; to gradually increase excess sludge flow rate as well as to initiate pydrohydrolysis to enhance hydrolysis. The start-up took 63 days and when it finished, the VSS organic loading reached 1.60 kg/(m3 x d), the average VSS biogas rate was 0.51 L/g, i. e. 15.3 m3/m3 sludge (96% water content), VSS and SS removals were 60.8% and 45.8%. This shows that the strategy is valid.