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.

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.

Measurement of potential alpha energy exposure and potential alpha energy concentration and estimating radiation dose of radon in Sari city in the north region of Iran.

In dwellings in Sari city in the northern region of Iran, the potential alpha energy exposure (PAEE) and potential alpha energy concentration (PAEC) have been measured and the radiation dose due to radon and its progenies has been estimated. In this study, the dosemeters DOSEman and SARAD GmbH (Germany), which are sensitive to alpha particles, were used. The population of the city of Sari is 495,369 people and the density of population is 116.5 people per km(2). A percentage of the total household population of Sari in areas of geographically different samples was selected. The PAEE, PAEC and radon concentration in four different seasons in a year in homes for sampling were measured. The mean PAEE due to indoor radon in homes of four cities in Sari city was estimated to be 28.23 Bq m(-3) and the mean PAEC was estimated to be 27.11 Bq m(-3). Also the mean indoor radon level was found to be 29.95 Bq m(-3). The annual dose equivalent is ∼0.0151 µSv y(-1). Measurement results show that the average PAEE, PAEC and radon concentration are higher in winter than in other seasons. This difference could be due to stillness and lack of air movement indoors in winter.