###### Abstract  
Fiber media filtration for combined Sewer overflow (CSO) treatment was evaluated in this work. Pilot-scale experiments of CSO treatment involve seven layers that form radial-type fiber media filters. The fiber media filter was characterized using analysis techniques and exhibited extremely high hydrophobicity and negative charge. The results obtained for a Sewer treatment plant at Tancheon in Seoul revealed potential for suspended solid, total organic carbon, and biochemical oxygen demand removal with efficiencies of 89.6%, 56%, and 42%, respectively. The results are consistent with the sieving effects and electrostatic repulsion between fiber media and pollutants. Head loss was induced by organic pollutants and was 10.5 cm after 20 h of operation. To mitigate the head loss induced by organic pollutants on the fiber media filter, sodium hypochlorite (NaClO) was used as a chemical backwashing agent. An NaClO concentration of 2000 mg/L with a soaking time of 24 h yielded an optimal head loss recovery of 96.2% of the initial head loss obtained for the virgin fiber media filter without media filter degradation. The result of the present study will provide practical insight and act as a technical guide for CSO treatment plant engineers. radial multimedia-filter; combined Sewer overflows NaClO soaking; removal mechanisms; organic pollutants +
Footnote †: journal: Medical Engineering  
liquor with high treatment quantities. Chemical treatment processes (e.g., ballasted flocculation processes) have improved sedimentation time by mixing with coagulants and media and effectively removing TSS, COD, BOD, P (phosphorus), algae, and heavy metals [4]. Primary treatments, such as constructed wetlands and setting tanks, could be used to remove TSS, COD, BOD, nutrients, micropollutants, coliform bacteria, and heavy metals [5]. Over the last two decades, various studies have examined the development of CSO treatment processes. Compared with other processes, coagulation-floculation treatments using coagulants such as polyaluminum chloride and alum exhibited higher removal efficiency for particulate matter; these form flocs when coagulants react with small particles and allow insoluble precipitates to form prior to flocculation of the solids and organic matter [6; 7]. A hydrodynamic vortex separator can remove suspended solids and sediments simultaneously with lower head loss than that encountered in other CSO treatments [8]. However, the removal efficiency of vortex separators is inadequate for CSO treatments [9]. Although, compared with other treatments, flocculation processes exhibit higher removal efficiency, the operation and maintenance costs are high due to the considerable coagulant injection required and sludge treatment costs associated with the operating process [10; 11]. In recent years, benefits of fiber media-based filtration over both vortex separators and coagulation and flocculation processes have been reported; compared with these processes, the fiber media filtration process has higher removal efficiency, higher biological resistance, low power consumption, and requires less land [12; 13; 14]. The development of fiber media filtration with high clogging prevention is essential for CSO treatments. During a physical backwashing, or backflush, tap water is injected in the opposite direction to that of filtration. The expectation is that this process will detach the cake layer loosely attached to the surface of the fiber media filter. Many researchers have reported that physical backwashing can improve the particulate and colloid cleaning efficiency of the filters [15; 16; 17; 18; 19; 20; 21; 22; 23]. However, control of organic pollutants in wastewater through physical backwashing in fiber media filters is difficult if such pollutants are attached to the surface of the media [18; 19; 20; 21; 22; 23]. Chemical cleaning is effective in removing organic pollutants from the fiber media filter.