Settling and dewatering characteristics of sludge from baker's yeast production wastewater treatment

The treatment of baker's yeast production wastewaters by a sequence of anaerobic and aerobic processes at the Pakmaya Izmit Plant results in the generation of three types of sludge, namely anaerobic, aerobic, and a mixture of the two. Formation of inorganic salts results in the accumulation of sludge in the bottom of the anaerobic reactors. Consequently, the volatile solids content of the sludges in the lower levels of the anaerobic reactors is lower. The higher levels of the anaerobic reactors are well mixed due to high circulation rate and biogas bubble rising. Settling and conditioning experiments were performed with all three types of sludge. The SVI values for all three types of sludge were low, indicating good settling characteristics. A high molecular cationic polyelectrolyte was found to be an effective conditioning chemical. Buchner Funnel Tests indicated that the SRF values for the anaerobic sludge were lower as compared to the aerobic sludge. The optimum dosage of the polymer for all three types of sludge was determined as 15 ml of 0.1% by weight solution per litre of sludge. Sludge thickening and dewatering with polymer conditioning have been applied successfully and economically on a full scale at the Pakmaya Plant using a combination of a rotary drum thickener and a belt filter, resulting in the production of sludge cake of 18–22% dry weight.