Design and modification of horizontal-flow roughing filter as water treatment at UGM retention pond

UGM Retention Pond as flood controller has its water supply from Belik River. Based on water quality monitoring results by the Environment Agency (BLH) of DIY in 2012-2016, the water status at the upstream area of Belik river has already contaminated before it flows to the retention pond. This study aims to make UGM Retention Pond not only as flood control, but also as a water treatment. The function can be fulfilled with the innovation of rough filter water type applied to horizontal flow, i.e. Horizontal-flow Roughing Filter. Mass balance analysis on the retention pond was calculated based on the assumption of the pond as a complete-mix reactor with BOD5 of 20.9 mg/L and TSS of 102 mg/L with discharge (Q) of 2.54 m³/s. The maximum target output produced for BOD₅ was 3 mg/L and TSS was 50 mg/L so the target of filtering efficiency was 94 . The analysis results showed the most optimal Horizontal-flow Roughing Filter was elongated beam-shaped design with length dimensions of 44.6 m, width of 2.5 m, and height of 1.7 m. Filter media used in the form of pebble (gravel) with the size of 24-16 mm and assumed to have permeability coefficient k = 0.1 m/s.