ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL IN ACTIVATED SLUDGE PROCESS

Abstract

Eithanced biological phosphorus removal (EBPR) is an acknowledged phenomenon applied to reduce phosphorus concentrations in wastewaters for preventing eutrophication in the receiving natural water bodies. Ifs well known fact that conventional EBPR process requires an optimal anaerobic phase to achieve net phosphorus removal from the wastewater. However, deteriorations in this process have been observed regularly for last few decades in full-scale waste water treatment plants, mainly due to excessive aeration in the aerobic zone, which increases amount of oxygen recycled to the anaerobic phase, due to which anaerobic conditions were disturbed. Therefore, some recent studies focused on achieving net phosphorus removal without using anaerobic phase, i.e. in completely aerobic conditions and obtained encouraging results. A laboratory scale aerobic baffled reactor was used to in the present work to study EBPR in single stage oxic process using molasses based synthetic wastewater similar in characteristics to the medium strength sewage. Dried powdered sludge from sludge drying beds of an activated sludge plant, treating municipal sewage, was added to the reactor in order to improve the settling characteristics of poly-P rich sludge. The reactor was initially started at 1211 FIRT that was gradually reduced to working HRT of 8 h. The experimental results showed that EBPR could be achieved in a baffled reactor without using anaerobic phase, which was assumed to be a key phase in conventional EBPR. Phosphorus concentration 0.3-0.8 mg/L in effluent can be obtained when Phosphorus concentration in the influent was about 10 mg/L, giving phosphorus removal efficiency in the range 92-97%. Concentration of phosphorus in the effluent was 0.6-1.7 mg/L (9 1-97% efficiency) and 9.3-11 mg/L (63-69% removal), when concentration of phosphorus in the influent was 20 and 30 mg/L respectively. A high COD removal efficiency of 82-89% was also observed in all the cases. It seems only around 20 mg/L phosphorus content in th influent e inuent can be treated using aerobic reactor,, with low dissolved oxygen concentration in the reactor.