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Background: This paper developed a system dynamics model to stimulate nitrate and ammonia in reservoirs. Most algae and plants in surface water use ammonia and nitrate as nitrogen sources. The role of these nutrients is evident on algae and also cyanobacterial growth. Nowadays, computer tools, especially mathematical modeling, are often used to manage these chemicals in water bodies.

Background: Phenolic compounds, phenol and phenol derivatives are environmental contaminants in some industrial effluents. Entrance of such substances into the environment causes severe environmental pollution, especially pollution of water resources. Biological treatment is a method that uses the potential of microorganisms to clean up contaminated environments. Among microorganisms, bacteria play an important role in treating wastewater contaminated with phenol. Objectives: This study aimed to examine the effects of Pseudomonas aeruginosa on degradation of phenol in wastewater contaminated with this pollutant. Methods: In this method, the growth rate of P. aeruginosa bacteria was investigated using different concentrations of salt and phenol. This is an experimental study conducted as a pilot in a batch reactor with different concentrations of phenol (25, 50, 100, 150, 300 and 600 mg L-1) and salt (0%, 0.5%, 1%, 2.5% and 5%) during 9, 12 and 15 hours. During three days, from 5 experimental and 3 control samples, 18 samples were taken a day forming a sample size of 54 samples for each phenol concentration. Given the number of phenol concentrations (n = 6), a total of 324 samples were analyzed using a spectrophotometer at a wavelength of 600 nm. Results: The phenol concentration of 600 mg L-1 was toxic for P. aeruginosa. However, at a certain concentration, it acts as a carbon source for P. aeruginosa. During investigations, it was found that increasing the concentration of phenol increases the rate of bacteria growth. The highest bacteria growth rate occurred was at the salt concentration of zero and phenol concentration of 600 mg L-1. Conclusions: The findings of the current study indicate that at high concentrations of salt, the growth of bacteria reduces so that it stops at a concentration of 50 mg L-1 (5%). Thus, the bacterium is halotolerant or halophilic. With an increase in phenol concentration, the growth rate increased. Phenol toxicity appears at a concentration of 600 mg L-1 .

Background:In advanced oxidation processes, pH has a significant effect on the removal efficiency of organic compounds. This study examined the effect of pH changes on the removal efficiency and kinetics of methyl tertiary butyl ether (MTBE) concentration in aquatic environment. Objectives: The primary objective of this study was to evaluate the effect of pH changes on removal kinetics of the mentioned compound, using H 2 O 2 /nZVI (nano zero-valent iron)/ultrasonic process, and its impact on the reaction rate. Materials and Methods: In order to create the right conditions for oxidation, first of all iron nanoparticles combined with H 2 O 2 oxidizer were synthesized, and then they were subjected to ultrasound waves and used in MTBE oxidation. In MTBE removal via H 2 O 2 / nZVI/Ultrasonic process, the effects of some parameters such as contact time (2 to 60 minutes), concentration of hydrogen peroxide (5 to 20 mL/L), concentrations of nZVI (0.15 to 0.45 g/L), MTBE concentrations (50 to 750 mg/L), and pH (2 to 9) were investigated. MTBE concentration analysis was performed using gas chromatography (GC). Results: According to this study, the best removal efficiency of 50 mg/L MTBE concentration in 89.56% under oxidation condition occurred when H 2 O 2 level equals to 10 mL/L, nZVI is 0.25 g/L at pH 3.5. The results showed that the increase or decrease of pH from 3.5 results in a loss of oxidation efficiency as well as reduction in the amount of k ap . In addition, the logarithmic changes curve of MTBE concentration showed that MTBE oxidation in H 2 O 2 /nZVI/ultrasonic method follows pseudo first order reactions. Conclusions: Changes of pH could remarkably affect the efficiency and oxidation rate of MTBE. In particular, the amount of k ap in terms of oxidation declines substantially by moving away from the optimum pH range. In this study, pH 3.5 was considered as the optimal pH in H 2 O 2 /nZVI/ultrasonic oxidation process, with the elimination of about 89.56% of the high MTBE concentration. In general, we can say that by adjusting pH in this range, the rate and efficiency of MTBE oxidation can be enhanced in H 2 O 2 /nZVI/ultrasonic method.

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Background: Low-cost anaerobic sequencing batch reactor (ASBR), which is widely used for controlling high-organic wastewater, is an effective method to remove chemical oxygen demand (COD). Objectives: The main objectives was evaluating the feasibility of using ASBR in the treatment of synthetic dairy wastewater, determining its removal efficiency, and assessing the effect of temperature on operating conditions to remove the COD effectively. Materials and Methods: The present study was conducted at a pilot scale system. Experiments were performed using a 20-L reactor and two storage tanks with the volume of 10 L. The effect of the variation of temperatures (20°C-35°C) and the effect of running cycles (10 runs) on the efficiency of COD removal by the ASBR process were investigated. Four heaters were used to produce the heat of the reactor. At first, raw wastewater in the primary tank was heated to the desirable temperature and then three more heaters continuously produce the heat in the reactor to operate system at the constant operating temperature in each run. Data were analyzed by SPSS 16through Pearson's correlation coefficient to analyze the association between these parameters. Results: The maximum COD removal rate was 89.7% at the organic loading of 4.5 g/L per day in a 24-hour cycle condition with reaction time of 21 hours and 30 minutes. The maximum biochemical oxygen demand (BOD5) removal rate was 91% and occurred at the first run. The amount of COD removal efficiency was higher at the first run in comparison to the third cycle (27.5%). BOD5 removal efficiency decreased up to 24.4% due to the drop of temperature in the reactor. Pearson correlation analysis showed a significant association between the temperature and the removal efficiencies (P < 0.01). Conclusions:The results of this study indicated that any decrease in the temperature caused reduction in system efficiency of removing BOD5 and COD. Temperature of 35°C is optimal for the removal of high organic load wastewater. ASBR can be used as an effective tool to treat dairy industry wastewater.

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