Effects of impurities on oxygen transfer rates in diffused aeration systems.

A series of unsteady-state reaeration tests were performed in a 500-L tank at 0.81-4.58 m3/h diffused-air flow rate and 288-302 K water temperature. Three different types of impurities: soybean oil, surfactant, and diatomaceous earth were doped to simulate the impurities in wastewaters and the effects of the impurities on the oxygen transfer rate were investigated. The ASCE and the two-zone oxygen mass-transfer models were used to analyze the unsteady-state reaeration data and the volumetric mass-transfer coefficients determined from the unsteady-state reaeration data were correlated as a function of the diffused-air flow rate, water temperature, and impurity concentration. The results showed that the alpha factors based on the ASCE model are less sensitive to the impurity concentration while the presence of the impurities significantly reduces the alpha factors in the gas bubble zone. The saturation DO concentration and volumetric oxygen mass-transfer rate can be predicted by the two-zone model along with the correlation obtained in this study.

Desorption of dye from activated carbon beds: effects of temperature, pH, and alcohol.

The adsorption isotherms of yellow and red dye solutions onto granular activated carbon at varying solution pHs (2-8). temperatures (15-50 degrees C), and alcohol concentrations (0-20%) were experimentally determined by batch tests and the Tóth model was found to best fit the adsorption isotherm data for varying solution pHs. temperatures, and alcohol concentrations. The maximum adsorption capacity was found to decrease with increasing solution pH and alcohol concentration and could be predicted by the correlation equations obtained in this study. A correlation equation was also obtained to account for the effects of solution temperature on the adsorption equilibrium constant. The 25 degrees C water was found to be a very poor regenerant for the carbon bed presaturated with the yellow dye compared with 20% alcohol solution. A simple equation was derived, based on non-linear wave propagation theory, to predict the desorption curves of activated carbon bed. Given presaturation concentration, bed density and void fraction, and adsorption isotherm, the wave propagation theory predicted the desorption curves quite satisfactorily.