In this paper, the effect of step geometry with five different tread values from 0.40 m to 0.60 m with an increment of 0.05 m and three different types of water namely potable, non-potable and recycled water on aeration efficiency of stepped cascade aeration was studied. Detailed experimental investigations were carried out for different hydraulic loading rates of 0.005 m2/s to 0.035 m2/s. All the experiments were conducted for nappe flow condition. Results revealed that overall aeration efficiency at standard conditions (E20) approaches maximum for t/h = 4, number of steps = 12, hydraulic loading rate = 0.02 to 0.025 m2/s for potable and non-potable water. In the case of recycled water maximum efficiency was achieved for t/h = 3.67. Results also revealed that stepped cascade aeration was found to be a very suitable option for enhancing DO content in treatment of waste water before discharging it to water bodies to save aquatic life.

Low efficiency of conventional aeration techniques and the excessive production and disposal of sludge are great concerns in biological wastewater treatment systems. The present study aimed to evaluate the active sludge method using batch reactors under continuous operation to determine the efficiency of aeration and sludge production through microbubble and nanobubble aeration. The results indicated that compared to microbubble aeration, nanobubble aeration increased the concentration of dissolved oxygen in the mixed liqueur of the reactor (from 2 to 4. 5 mg/l), while reducing the production of excess sludge from 100 to 40 ml/g (SRT: 15-40 d). With the same SRT duration, these values were within the range of 160-70 ml/g using fine-bubble aeration. According to the results, nanobubble aeration could increase the efficiency of aeration, thereby increasing the capacity of the treatment plant and reducing the costs of biological wastewater treatment.

Advanced Oxidation Processes (AOPs) are the effective processes in treatment of the various wastewaters contaminated with hazardous organic pollutants. In this work, decolorization of Acid Blue 74 in the UV/H2O2 process by using a batch photochemical reactor equipped with a 15 W low pressure mercury lamp (Osram) and aeration system as stirrer was studied. At the short time decolorization was complete and follows first order kinetic with respect of dye concentration. The rate of decolorization at the maximum absorption wavelength was monitored with spectrophotometric analysis. Effect of the important parameters such as initial concentration of H2O2, pH and initial concentration of dye on the dye decolorization was studied. It was found that the rate of decolorization increase with increase in H2O2 concentration up to 0.0294 mole.L-¹. The great rate of decolorization observed at the pH=3. With increasing the initial concentration of the dye up to 6.43×10-5 M, initial reaction rate was increased.

Linear Alkyl Benzene Sulphonate Acids (LAS) are one of the anionic surfactants that are produced and used in large quantities in different countries and find their way into the natural environment through sewer systems.These compounds may potentially cause environmental hazards in such surface waters as rivers. It is, therefore, necessary to remove as much of these compounds as possible by biological processes in wastewater treatment plants. For this purpose, four parallel biological reactors were constructed that used the conventional activated sludge and aeration tanks with fixed bed on the bench scale in order to evaluate the removal efficiency of LAS.The reactors were operated under conditions similar to domestic wastewater treatment plants. Parameters of interest were measured according to standard methods and ANOVA and T-test were used for the statistical analysis of the data. The results showed that aeration tanks with fixed beds yielded higher values of LAS and COD removal and air consumption compared to the conventional activated sludge system. It was shown that the two systems studied achieved LAS removal efficiencies of 96% and 94% for an influent LAS concentration of 5 mg/L. Further, it was found that the effluents from both systems satisfied water quality standards for discharge into surface waters (<1.5 mg/L) and into ground waters (<.5 mg/L). At LAS concentrations higher than 5 mg/Li, the conventional activated sludge system did not have the required efficiency and its effluent did not meet the environmental discharge standards. In contrast, aeration tanks with fixed bed achieved a removal efficiency of 97% at higher concentrations (15 and 20 mg/L) and were capable of reducing the amount of effluent LAS concentration. Therefore the aeration tank system should be recommended for high LAS concentrations in the influent.

The effluent of the beverage industry has a higher yield, which is biological. Locations The overall objective of this study is to evaluate the efficiency of the activated sludge process with extensive aeration and sludge return to reduce the COD of beverage industry effluents. For evaluation, a 20-liter tank was completely used anaerobically, from which the artificial effluent was transferred to the pilot. The organic load increased from 1.03 kgCOD/m3.day to 1.93 kgCOD/m3.day. In this study, the COD parameter was used to measure the pollution of the beverage industry effluent and its working cycle was 24 hours. Hydraulic retention time, temperature and pH were also measured. The results of this process showed that with a final organic load of kg COD/m3.day of 1.93, the removal efficiency was 90%, which is part of the removal efficiency (20 to 30%) of the anaerobic tank used in the first pilot. By examining the hydraulic retention times of 6, 12, 18 and 24 hours, the highest efficiency was obtained in the retention time of 24 hours and in the research process, the pH was between 7 and 9 and the temperature was in the mesophilic range. Therefore, it can be concluded that the process of activated sludge with extensive aeration and sludge return is effective in the treatment of effluents of beverage industries with medium organic load.