Efficiency studies of modified IFAS-OSA system upgraded by an anoxic sludge holding tank

www.nature.com/scientificreports OPEN Efficiency studies of modified IFAS‑OSA system upgraded by an anoxic sludge holding tank Mansour Fazelipour1, Afshin Takdastan2, Seyed Mehdi Borghei3, Neda Kiasat4, Marcin Glodniok5* & Paweł Zawartka5 An upgraded integrated fixed-film activated sludge-oxic settling anoxic (IFAS-OSA) system is a new technology for reducing nutrients and excess sludge. The results showed that the average TN removal efficiency of the IFAS-OSA system was gradually increased up to 7.5%, while the PO4–3-P removal efficiency increased up-to 27%, compared with that of the IFAS system. The COD removal efficiency of the IFAS-OSA system was slightly increased up-to 5.4% and TSS removal efficiency increased up to 10.5% compared with the control system. Biomass yield coefficient (Yobs) in the IFAS and IFAS-OSA systems were 0.44 and 0.24 (gr MLSS/ gr COD). Hence, sludge production decreased by 45%. The average SVI was decreased by 48% in IFAS-OSA system compared with IFAS. This study demonstrated the better performance of the IFAS-OSA system compared to that of the IFAS system. Abbreviations ASHT Anoxic sludge holding tank BNR Biological nutrient removal BOD Biological oxygen demand CAS Conventional activated sludge CFU Colony forming unit COD Chemical oxygen demand DO Dissolved oxygen ESR Excess sludge reduction HRT Hydraulic retention time IFAS Integrated fixed-film activated sludge IFAS-OSA Integrated fixed film activated sludge-oxic settling anoxic ITS Internal spacer region MLE Modified Ludzack-Ettinger MLSS Mixed liquor suspended solids NH4+-N Ammonium nitrogen NO3–N Nitrate nitrogen ORP Oxidation–reduction potential OLR Organic loading rate OSA Oxic-settling-anoxic OUR Oxygen uptake rate PCR–RFLP Polymerase chain reaction-restriction fragment length polymorphism PAO Phosphorus accumulating organisms PO4-3-P Orthophosphate-phosphorus Q Excess Excess sludge flow rate RAS Return activated sludge SBI Sludge biotic index SDA Sabouraud dextrose agar 1 Department of Environmental Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran. 2Environmental Health Department, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. 3Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran. 4Department of Medical Mycology, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. 5Department of Water Protection, Central Mining Institute, Katowice, Poland. *email: mglodniok@ gig.eu Scientific Reports | (2021) 11:24205 | https://doi.org/10.1038/s41598-021-03556-6 1 Vol.:(0123456789) www.nature.com/scientificreports/ SRT Solid retention time SVI Sludge volume index TN Total nitrogen TSS Total suspended solids TKN Total Kjeldahl nitrogen Yobs Observed yield coefficient The nitrification and denitrification processes are of high importance in wastewater treatment plants because of the ammonia toxicity, oxygen demand, algae bloom and eutrophication in water b odies14,16,17. Insufficiently treated sewage are carrying plenty of nutrients and micropollutants that pose serious threats to receiving r ivers34. Another issue is the excess sludge which is generated from the biological treatment of wastewaters and must be disposed of in a safe and cost-effective manner for example in agricultural p roducts15,23. Reducing the nutrients and excess sludge in biological processes can be done by various techniques and methods. Some of these techniques consist of oxic-settling-anaerobic (OSA) process18,28, oxidation of the sludge by chlorine and o zone5,11. OSA technique is also a suitable solution for enhancement organic matter and nutrient (N & P) pollutants removal which significantly reduces biological excess sludge. This technology usually includes an aeration tank, a settling tank, and an anoxic/anaerobic tank in the return activated sludge line of the aerobic s ystems1,33,35,37. Furthermore, some of the methods include the modified Ludzack-Ettinger (MLE) and integrated fixed-film activated sludge (IFAS)6,26. The IFAS technology increases the solid retention time without overloading the settling tank with solids and without the need to expand the aeration tank4,39. Combined with, OSA system enhances nitrification and denitrification and decreasing the excess sludge production and increases efficiency of IFAS p rocess20. Chudoba et al.8 compared the sludge yield of an OSA process with that of a CAS process and found that reduction of sludge yield from 0.48 to 0.13, the in the OSA system caused its reduction from 20 to 60%. The SVI was much lower and the ORP of -250 mV in the anaerobic tank showed a reduction of 36% in comparison with the ORP of + 100 mV. The OSA process had the excess sludge reduction of 58% compared with that of the CAS system8. In Saby et al.25 also conducted similar research with CAS-OSA system. In his research ORP values in the anoxic and aerobic tanks were -250 mV and + 100 mV, respectively. The results revealed that the OSA process produced much less excess sludge than the control s ystem25. Another researcher studied the OSA process for the reduction of biological sludge and found that the MLSS in a CAS-OSA process was reduced from 3000 mg/L to 2500 mg/L as the cellular mass production coefficient was reduced from 0.52 to 0.2 g biomass/g COD after 50 days with an ORP of -250 mV10. In Vitanza et al.29 proved with his research on OSA technique in an anaerobic stage of the CAS system, that besides the good efficiency of the OSA system in the removal of COD, BOD, and nitrogen, the mass production coefficient (Y) was reduced from 0.6 to 0.4 g biomass/g COD. The ORP value was -160 mV while the COD, ammonia nitrogen, and phosphorus removal efficiencies were 76%, 82.5%, and 28%, respectively29. Also in research from Vitanza et al.30 observed the reduction of the excess sludge production in OSA technique of 49.6 ± 20.7% compared to the CAS system. Martins et al.18 research from 2020 has proven that better wastewater treatment performance was achieved using the OSA system ( BOD5: 87%, TKN: 92%, N H4+–N: 94%) when 4+ compared with the CAS system (BOD5: 76%, TKN: 74%, NH –N: 78%), considering the organic matter and nitrogen removal rates. In Corsino et. al.9. performed studies about the coupling of the OSA process with a thermal treatment at moderate temperature. The combination of the OSA process with the thermic treatment at moderate temperature (35 °C) enabled a very high efficiency of sludge minimization (80%), but lower nutrient reduction. Those research show a great potential for modification of oxic-settling-anaerobic technique. The aim of this study was to investigate the performance of the new upgraded IFAS-OSA system in removing nitrogen, phosphorus, chemical oxygen demand (COD), and reducing excess sludge. The novelty of this study was the development of a new modified IFAS-OSA system for the first time by adding an anoxic s (...truncated)