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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‐OSA2h and IFAS‐OSA4h 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. [ABSTRACT FROM AUTHOR]

Integrated fixed film activated sludge-oxic settling anoxic system (IFAS-OSA) is a new, modified system for excess-sludge reduction. In this research, the efficiency of the IFAS-OSA system in biological excess-sludge reduction with the addition of an anoxic sludge-holding tank to the return line of the system was studied. The results showed that the average oxidation reduction potentials (ORPs) in the IFASAerobic , IFASRAS , IFAS-OSA2 h , and IFAS-OSA4 h processes were +80±15 , −62±22,–102±8 , and −140±13 mV , respectively. The average values of Yobs in the IFAS, IFAS-OSA2 h , and IFAS-OSA4 h processes were 0.43±0.01 , 0.31±0.02 , and 0.23±0.01 g MLSS/g COD, respectively. Accordingly, in the IFAS-OSA2 h and IFAS-OSA4 h processes, the sludge production was reduced by 27.9% and 46.5%, and the excess sludge was reduced by 13.65% and 22%, respectively, compared with the control system. Furthermore, as the average SVIs reached 95±12,63±6 , and 49±4 mL/g , the TSS values in the effluents of the IFAS, IFAS-OSA2 h , and IFAS-OSA4 h processes reached 16.5±3 , 7.2±1.5 , and 5.5±1.2 mg/L , respectively. The average percentages of total nitrogen (TN) removal efficiency in the IFAS, IFAS-OSA2 h , and IFAS-OSA4 h processes were 78.56±2.46 , 83.60±0.92 , and 85.03±1.69 , respectively, whereas the percentages of phosphorus removal efficiency in these processes were 32.69±8.25 , 36.35±6.73 , and 39.87±3.61 , respectively. This study revealed that the modified IFAS-OSA system had a more efficient performance than the IFAS system. [ABSTRACT FROM AUTHOR]

Optimized methods for simultaneous removal of nitrate, nitrite and ammonium are important features of nutrient removal. Nitrogen removal efficiency in an intermittently aerated sequencing batch reactor (IA-SBR) with multiple filling events was studied. No external carbon source was added and three filling events were considered. Oxidationreduction potential (ORP) and pH curve at solids retention time (SRT) of 20 d were analyzed. Effects of three organic loading rates (OLR), 0.67, 1.0 and 1.5 kgCOD/m3d, and three nitrogen loading rates (NLR), 0.054, 0.1 and 0.15 kgN/m3d, on nitrogen removal were studied. Nitrate Apex in pH curve and Nitrate Knee in ORP profile indicated that the end of denitrification would be achieved sooner. The kinetic coefficients of endogenous decay (kd) and yield (Y) were identified to evaluate heterotrophic specific denitrification rate (SDNRb). In period 2 at NLR of 0.054 kgN/m3d and considering 2 anoxic and 3 aerobic phases, nitrogen removal efficiency was 91.43%. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Enhanced nutrient removal was achieved in a hybrid 5-stage Bardenpho-MBBR system. • Maximum nitrogen and phosphorous removal efficiencies were about 93% and 95%. • An anaerobic HRT of 2 h and nitrate recycle ratio R of 2 were the suitable operational values. • Attached biofilm nitrifying activity was about 4 times higher than in suspended biomass. • Suspended biomass showed higher COD removal according to oxygen uptake rates. Abstract Nutrient pollution has become a global environmental issue. Innovative biological nutrient removal (BNR) processes are needed to overcome the drawbacks of conventional technologies. This study evaluates the potential of a hybrid 5-stage Bardenpho - moving bed biofilm reactor (MBBR) process for organic carbon and nutrient removal from municipal wastewater at different hydraulic retention time (HRT) and nitrate recycle ratio (R). Response surface methodology (RSM) based on a central composite design (CCD) of thirteen experiments was applied to optimize the nitrogen and phosphorus conversion of the treatment system. High removal efficiencies of about 98.20%, 92.54%, 94.70% and 96.50% for total chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) and ammonium, were achieved, respectively. The best performance was observed at HRT of 2, 4, 6, 2.67 and 1.07 h correspondingly in the anaerobic, first anoxic, first aerobic, second anoxic and second aerobic compartments, resulting in a total HRT of 15.74 h with a nitrate recycle ratio of 2. Biofilm nitrifying activity was four times higher than in suspended biomass. The hybrid 5-stage Bardenpho-MBBR process enhanced biological nutrient removal at comparatively short HRT and low R ratio due to biofilm contribution to the conversion. [ABSTRACT FROM AUTHOR]