Biological removal of nutrients (N & P) from urban wastewater with a modified integrated fixed-film activated sludge-oxic settling anoxic system using an anoxic sludge holding tank

In this research, the efficiency of the integrated fixed-film activated sludge-oxic settling anoxic (IFAS-OSA) system in biological nutrient removal was studied. The oxic-settling anoxic (OSA) process is known as a cost effective way to reduce the nutrients (nitrogen and Phosphorus). According to the results, the percentages of total nitrogen removal efficiency in the IFAS, IFAS-OSA(2h) and IFAS-OSA(4h) systems were 78.56 +/- 2.46, 83.60 +/- 0.92 and 85.03 +/- 1.69, respectively, while the percentages of phosphorus removal efficiency in these systems were 32.69 +/- 8.25, 36.35 +/- 6.73 and 39.87 +/- 3.61, respectively. The PCR-RFLP method showed that C. albicans had the greatest prevalence (n = 36, 90%). Moreover, Vorticella convallaria was identified as the most abundant species of protozoa. The current research demonstrated that the efficiency of the modified IFAS-OSA process was higher than that of IFAS in the removal of nutrients (TN and PO43-P) and can be a suitable method for upgrading the wastewater treatment plants worldwide.