Effect of calcium nitrate dosing frequency on biological conditioning of sludge

Degradable organics in the excess sludge can be decomposed and sped up by denitrifying bacteria with Ca(NO3)2 added, which can enhance the dewaterability of sludge. With the total NO3- dosage of 100 mg·g-1 TS, and the dosing frequencies of Ca(NO3)2 divided into 1, 2, 3 and 6 times during six days respectively, the dewaterability of sludge was observed. It was shown that the sludge CST could be reduced by 65.0%, the SRF was reduced by 73.2%, the protein in extracellular polymeric substance of sludge was reduced, and the protein in S-EPS and LB-EPS was reduced from 13.47 mg·L-1, 11.66 mg·L-1 to 0.52 mg·L-1, 1.43 mg·L-1respectiveLy, the Zeta potential tend to become electroneutral after Ca(NO3)2 added, which was helpful for improve sludge dewaterability. The results also indicated that sludge dewaterability could be improved greatly with Ca (NO3)2 added at one-time, since more nitrite could be produced, which could help release the microbial cytoplasm, the released organics in the microbial cytoplasm, could be used by denitrifying bacteria as carbon source.