Effects of Filtration Rate in High-Rate Filters for Pretreating Textile Wastewater

This study is to evaluate the performance of a high-rate filter (HRF) as an alternative to conventional primary sedimentation processes. In this study, the effect of HRF filtration rate (100-400 m/d) was evaluated to treat textile wastewater, which generally exhibits harsh characteristics such as high chemical oxygen demand (COD), suspended solids (SS), color, and salinity; BOD 746.0 mg/L, COD 492.0 mg/L, T-N 34.7 mg/L, T-P 7.0 mg/L, SS 296.4 mg/L, and color 647.0 units. The packed depths in the HRF was 0.6 m for cube sponge media (CSM). As a result, the removal efficiencies of HRF with filtration rate (FR) were as follows: SS 21.3-38.3%, COD 11.2-29.2%, BOD 15.4-34.5%, color 5.4-14.5%, T-N 5.8-14.5%, and T-P 3.8-8.1%. These results showed a decrease of filtration efficiencies with increasing FR of the HRF. In particular, the removal efficiencies of SS and BOD was 10-20% higher than that of nutrient and color. This resultes in higher particulate in SS and BOD than that in color and nutrient. The CSM also was effective in reducing SS and BOD, owing to high specific surface area being three times that of existing plastic media. Backwashing cycle of the HRF bed due to a bed clogging with filtration time ranged from 12 h to 24 h. To further enhance the filtration efficiency of the HRF with FR, the process needs to operate at a lower FR and be coupled with coagulation.