Molecular detection of microbial community in a nitrifying–denitrifying activated sludge system

Presence of different forms of ammonia in the wastewater treatment plants are toxic to aquatic life and promote eutrophication in receiving water bodies. It becomes imperative to lower the ammonia concentration in the effluents for which characterization of microbial diversity is foremost objective. Study was planned to identify the diversity of nitrifiers and denitrifiers from activated sludge using PCR technique. Cultural techniques revealed high bacterial diversity was found in the aeration tank where majority of the isolates belongs to class γ proteobacteria followed by β proteobacteria suggesting the adaptability of these groups. Presence of Nitrosomonas europaea revealed better ammonium oxidation condition at longer SRT of 6 and 7 d with DO concentration of 2.5 mg/L. As a part of NOB, Nitrospira sp. found to be more dominant than Nitrobacter winogradskyi as its detection was achieved in all samples of 6 and 7 d SRT, while later was detected only on 7 d SRT. Use of cultural techniques in combination with PCR analysis with 16S rRNA approach revealed Pseudomonas aeruginosa as important denitrifier. Highest removal efficiencies of COD, BOD, TN and NH 4 + – N were found to be 81, 78, 70 and 69% respectively at optimized SRT of 7 d.