Optimization of Energy Consumption and Mass Transfer Parameters in a Surface Aeration Vessel.

This paper reports tests on a lab-scale surface aeration vessel was equipped with a Rushton turbine to examine its performance in terms of standard aeration efficiency (SAE), mixing time, and void fraction characteristics. These characteristics were investigated by tests using variations of rotor speed, impeller immersion depth, and water level. Results showed that variation of impeller immersion depth had a greater effect on the SAE compared to variation of water level. Moreover, the SAE increased with rotor speeds up to about 150 to 200 rpm and then decreased. In addition, void fraction improved by impeller immersion depth and rotor speed enhancement; however, mixing time and power number were reduced as rotor speed increased. According to the response surface methodology statistical optimizations, optimum values for rotor speed, impeller immersion depth, and water level were 168.90 rpm, 25 mm, and 30 cm, respectively, to achieve the maximum value of SAE.

Combined physico-chemical treatment of secondary settled municipal wastewater in a multifunctional reactor.

In this paper, the physico-chemical treatment of municipal wastewater for the simultaneous removal of pollutant indicators (chemical oxygen demand (COD) and total coliforms) and organic contaminants (total phenols) was investigated and assessed. A secondary settled effluent was subjected to coagulation, disinfection and absorption in a multifunctional reactor by dosing, simultaneously, aluminum polychloride (dose range: 0-150 µL/L), natural zeolites (dose range: 0-150 mg/L), sodium hypochlorite (dose range: 0-7.5 mg/L) and powder activated carbon (dose range: 0-30 mg/L). The treatment process was optimized using computational fluid dynamics (CFD) and response surface methodology. Specifically, a Latin square technique was employed to generate 16 combinations of treating agent types and concentrations which were pilot tested on an 8 m(3)/h multifunctional reactor fed by a secondary effluent with COD and total coliform concentrations ranging from ≈20 to 120 mg/L and from 10(5) to 10(6) CFU/100 mL, respectively. Results were promising, indicating that removal yields up to 71% in COD and 5.4 log in total coliforms were obtained using an optimal combination of aluminum polychloride (dose range ≈ 84-106 µL/L), powder activated carbon ≈ 5 mg/L, natural zeolite (dose range ≈ 34-70 mg/L) and sodium hypochlorite (dose range ≈ 3.4-5.6 mg/L), with all treating agents playing a statistically significant role in determining the overall treatment performance. Remarkably, the combined process was also able to remove ≈ 50% of total phenols, a micropollutant known to be recalcitrant to conventional wastewater treatments.