The role of mixing in potassium ferrate(VI) consumption kinetics and disinfection of bypass wastewater

Bypass wastewaters need an appropriate auxiliary treatment to address their broad range of chemical and bacterial characteristics. The dual capacity of potassium ferrate(VI) as disinfectant/oxidant and coagulant may be useful in a sustainable process retrofit to provide adequate treatment to such wastewaters. However, the engineering aspects of potassium ferrate(VI) based technology to retrofit within existing coagulation-flocculation-sedimentation basins have not been studied. This study investigated, for the first time, the role of rapid mixing on the rate of potassium ferrate(VI) decay and disinfection in bypass wastewaters from extreme wet weather flow events. First-order, second-order, and double exponential models were fit to the potassium ferrate(VI) consumption data, and the double exponential model was able to represent the potassium ferrate(VI) decay in all conditions with a high coefficient of determination and low mean square error. In addition, Chick-Watson and Hom models were tested in this study, and both fit the E. coli disinfection results. The rates of potassium ferrate(VI) consumption and disinfection derived from the models were higher using 500–1000 rpm rapid mixing speeds than they were when magnetic stirrer mixing was used for the same initial dosage and wastewater sample. There was no significant increase in the potassium ferrate(VI) consumption or disinfection rates with the increase of the rapid mixing speeds from 500 to 1000 rpm which revealed that the reactions were kinetically controlled. The coagulation capability of potassium ferrate(VI) enhanced the sedimentation ability and contributed almost the same as the chemical disinfection capability to the overall E. coli removal. This study suggests that potassium ferrate(VI) can be implemented in existing facilities that mix coagulants to enhance primary sedimentation, yet potassium ferrate(VI) can provide both disinfection and coagulation at lower mixing speeds.