ALPHA. AND BETA FACTORS IN AERATION FOR WASTEWATER TREATMENT

Abstract

Aeration is defined as a gas-liquid mass-transfer process in which interface diffusion occurs when a driving force is created by a departure from equilibrium. The areation systems are widely applied to aerobic biolgical treatment of wastewaters. The parameter which is directly related to the oxygen transfer is the overall-mass transfer coefficient, KLa. It is a measure of rate of oxygen transfer into the aeration system. It is affected by a number of factors — temperature, degree of mixing, wastewater character- istics, and other minor factors. In this work, studies were carried out to determine the values of alpha ( ratio of KLa tapwater to KLa wastewater ), a and Beta, III and to see the variation of alpha with the intensity of mixing. The aeration studies on both tap water and wastewater were conducted on a bench scale aeration tank using surface aerator. To find the variation of alpha with levels of mixing, the rotational speeds of impeller were varied from 100-200 rpm. The experimentations were also carried out with two different impellers configurations. The values of alpha varied from 0.77 to 0.91 while beta was found to be around 0,91. The variatiion of a with rpm followed a sag curve passing through a minimum at medium levels of mixing. The impeller type 11 was found to be more efficient than impeller type I. The studies can further be done with different wastewater and impeller configurations.