Comparison of Dewatering Effects of Chemical Conditioning Method for Thermophilic and Mesophilic Anaerobic Digested Sewages Sludge

Abstract

Anaerobic digestion is the most prevalent stabilization method used in treating waste activated sludge. However, the digested sludge produced has always been difficult to dehydrate. In this study, mesophilic anaerobic digested sludge and thermophilic anaerobic digested sludge were used to compare the dewatering capacity of two chemical coagulants: high-performance polyaluminum chloride (HPAC) and FeCl3. For mesophilic anaerobic digestion, 5% g/g total suspended solids (TSS) was the optimal dose of FeCl3 and HPAC to improve dewaterability. In addition, HPAC was superior to ferric chloride in the removal of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound extracellular polymeric substances (TB-EPS). For thermophilic anaerobic sludge, HPAC is more effective compared with FeCl3 in improving the dewaterability. FeCl3 could effectively remove TB-EPS, while HPAC had better removal efficiency on soluble extracellular polymeric substances (S-EPS) and LB-EPS. Both chemical coagulants have greater potential to degrade EPS during thermophilic anaerobic digestion sludge treatment. The results of the supernatants characterization after conditioning illustrated that FeCl3 and HPAC have similar removal efficiency on organic matter, but HPAC could remove additional small molecular weight compounds, particularly when conditioning with the thermophilic anaerobic sludge; however, there was no apparent changes when using FeCl3.