Environmental performance and microbial investigation of a single stage aerobic integrated fixed-film activated sludge (IFAS) reactor treating municipal wastewater

• More than 90% removal of COD, BOD, and TSS achieved in the current system.
• Removal of bio-indicators and pathogenic bacteria is examined in the current system.
• Respirometric tests showed dominancy of attached biomass in overall treatment.

Due to exhausting natural and conventional water resources, it is necessary that the existing wastewater management practices should introduce small-scale treatment technologies. In this purview, technical assessment of a single stage integrated fixed-film activated sludge (IFAS) reactor, treating municipal wastewater, was carried out at optimized operating conditions i.e. dissolved oxygen (D.O.), ∼3 mg L−1; hydraulic retention time (HRT), 6.9 h; return activated sludge (RAS) rate, 160–175%; waste activated sludge (WAS) rate, 1.1 m3 d−1; sludge age, ∼7 d. The start-up period for the reactor was 33 days and after this, the reactor was run for three months. The suspended and attached biomass worked together to maintain an average removal rate of ∼92% for chemical oxygen demand (COD), ∼91% for biological oxygen demand (BOD), ∼90% for total suspended solids (TSS), ∼88% for total nitrogen (TN) and 50% for total phosphorus (TP), respectively under optimized conditions. Almost two times of the suspended biomass was observed in attached phase, which provided high treatment performance of the system with respect to overall pollutants removals. Scanning electron microscope observation of suspended and attached microbial community showed that biofilm was more homogeneous and porous than the suspended biomass. Microbial results revealed 2.2 and 2.4 log reduction of total coliforms (TC) and faecal coliforms (FC), respectively. E. coli was found to be achieved higher removal efficiency (>99%) among all the selected pathogens (E. coli; Salmonella spp. and Shigella spp.). Respirometric characterization of biomass showed that attached biomass was found to be dominating in the overall removal of pollutants.