Keywords: thermal treatment, poly P, poly phosphate, COD solubilisation, anaerobic phosphorous release, EBPR sludge, enhanced biological phosphorous removal, lime, temperature, anaerobic treatment
Combinative treatment (thermal–anaerobic) of EBPR sludge for the enhanced release and recovery of phosphorous
In the present study an attempt has been made to recover phosphorus in the presence of poly P and to disintegrate sludge through combinative treatment. Primarily the sludge was treated by thermal method at a temperature range of 40° to 90°C. During thermal treatment, enhanced biological phosphorous removal (EBPR) sludge releases poly P and is found to be maximum at 60°C for three hours. Increase in temperature over 60°C causes degradation of the released poly P. The COD solubilisation and release for 60°C were found to be 12.4% and 1,020 mg/L. Secondary release of phosphorous was done by subjecting thermally treated sludge samples to anaerobic conditions for eight hours. During anaerobic treatment, TP release and solublisation were found to be higher at temperature 60°C and was found to be 58 mg/L and 24.1% respectively. Anaerobic treatment did not affect the thermally released poly P. TP recovery was carried out using a coagulant lime. A coagulant dosage of 2:1 mole ratio was used to recover 90% of P selectively for the temperature 40°C to 60°C. Temperature in excess 60°C demands more coagulant dosage and was not selective in precipitating phosphorous.