آب و فاضلاب (Sep 2007)
Filter Backwash Water Treatment Using Dissolved Air Flotation Method
Abstract
Studies of turbidity removal in the past led to the development of coagulation and filtration processes. New processes are, nowadays, under development for improving upon impurity removal from water. In the present study, a DAF pilot plant and the jar test were used to investigate the optimum conditions for Turbidity, COD, HPC, and MPN removal. The goal of this study was to evaluate continuous inflow DAF performance on a pilot scale in improving the quality of spent filter backwash water in Isfahan Water Treatment Plant (WTP). The results showed that the continuous flow DAF using PACl as coagulant for removal of a turbidity level above 1000 NTU recorded efficiency levels of 97%, 72%, 75%, and 99% for COD, HPC, and MPN, respectively. Statistical analyses indicated that increasing saturation recycle rate led to improved removal of impurity and that the optimum saturation pressure was 4-5 atm for a recycle rate of 20-25 percent. It is concluded that the continuous flow DAF can be an efficient method for turbidity, COD, and bacterial removal from filter backwash water in Isfahan WTP. The turbidity and bacterial removal efficiencies in the coagulation method with sedimentation were reported to be up to 70 and 65 percent, while in this study, using DAF with PACl as coagulant, turbidity, COD, and bacterial removal efficiencies were as high as 97, 72 and 72 percent, respectively. A DAF system is, therefore, recommended for Isfahan WTP filter backwash water recovery and the designs and operation of this system should be a first concern for Isfahan WTP authorities.
