The investigation of biological removal of nitrogen and phosphorous from domestic wastewater by inserting anaerobic/anoxic holding tank in the return sludge line of MLE-OSA modified system
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In this study, the biological removal of nitrogen and phosphorous (BNR) was investigated by applying modified MLE-OSA technique. To conduct this study, three pilot plants scale were designed and established: 1) MLE similar to the current method used in Sari Wastewater Treatment Plant as control reactor 2) MLE-OSA4 with 4-h hydrolic retention time in sludge holding tank 3) MLE-OSA6 with 6-h hydrolic retention time in sludge holding tank. In this modified process for combining OSA technique with MLE system, two anaerobic/anoxic tanks were installed in the return sludge line with capacities of 70 and 107 l for MLE-OSA4 and MLE-OSA6, respectively. To set up the process, outlet sewage of the primary settlement tank of Sari Wastewater Treatment Plant was used. After a period of 45–60 days and reaching the steady state, the reactors were operated and the main, controllable parameters and laboratory experiments such as DO, ORP, Temperature, pH, COD, BOD5, MLSS, and nutrients (N&P) were precisely analyzed according to standard methods for examination of water and wastewater. The results showed that utilizing MLE-OSA system with 4 and 6 h hydraulic retention times decreased the ORP by around 109 ± 9 to 160 ± 25 mv and increased sludge retention time from 29 to 33 days. Moreover the percentages of phosphorus removal efficiency in MLE, MLE-OSA4 and MLE-OSA6 processes were 31 ± 5.2, 36.8 ± 1.9, and 39.4 ± 1.9 and the percentages of total nitrogen removal efficiency were 67.2 ± 7.6, 75.6 ± 4.8, and 78.5 ± 2.2 respectively. This study revealed that the modified MLE-OSA is more efficient than MLE for P and N removal. Hence it can replace this process.
KeywordsDomestic wastewater MLE-OSA Sludge holding tank Nitrogen Phosphorous Biological nutrient removal
This article is extracted from the Ph.D thesis and belongs to the Ahvaz Branch Islamic Azad University. It is also a part of the research project No 7337/150. The authors would like to aknowledge Mazandaran Water & Wastewater Co, Health Science Research Center of Mazandaran University of Medical Sciences, Mr. Ehsan Mehdizadeh, the responsible operator of the Sari Sewage Treatment Plant and his colleagues, the officials and staff of Sari Sewage Treatment Plant. Finally we appreciate the lab chief for his support of this project.
Compliance with ethical standards
Conflict of interest
The author declare that they have no conflict of interest.
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