Fiber filter as an alternative to the process of flocculation-sedimentation for water treatment

The conventional treatment for production of drinking water from surface water generally consists of coagulation, flocculation, sedimentation and sand filtration. One of the main disadvantages of the conventional process combining sedimentation and filtration is the rather long residence time. This is mostly due to the flocculation and sedimentation phases (typically 2 h). The fiber filter recently developed has been very successful for the tertiary treatment of biologically treated sewage effluents (more than 2 millions m3/d treated by this technology in Korea). In this paper, a different application of this filter to drinking water production was tested. In this case, the fiber filter (with in-line coagulation) was used as an alternative to the process of flocculation and sedimentation. Even though the first design of the fiber filter showed good removal efficiency, the filter was modified in order to improve its performance commensurate with the tightening of regulation on the water quality regulation. In this study, the filtration efficiency of the newly designed filter was estimated using a range of filtration velocities from 60 to 100 m/h and a small dosage of coagulant (1-3 mg/L) injected in-line. The polymeric coagulant (PAC: 11% as Al2O3) was used during this experiment. The optimal operation conditions were determined based on the performance and filtration time. Through these experiments, it was shown that the new fiber filter design was very efficient for particle removal at a filtration velocity of 60 m/h (1500 m3/d) and 1 mg/L coagulant dosage, and these were considered as the optimal operating conditions. Through the direct suspended solids (SS) measurement it was verified that backwash efficiencies were also very good.