Abstract:
This research studied effects of low COD concentrations to the efficiencies of anaerobic filter/aerobic sand biofilter systems and effects of media surface area in anaerobic filter. Anaerobic filter consisted of 4 tanks in series, each tank had retention time of 0.5 day, total retention time of 2 days. Aerobic sand biofilter contained 0.60 m. medium sand with air ventilation pipe in the bottom to filter solids from anaerobic tanks and remove odorous gas with air in sand layer. Synthetic wastewater was prepared from sugar (sucrose) at 1,500, 1,000, 500, and 200 mg-COD/l, and flowed constantly to reactors at 31.2 liter per day. Results found that total COD removal efficiencies were about 92-98%, which 70-95% came from anaerobic filters. COD in anaerobic process were most removed in the first 0.5-day retention time tank, accounted for 70-90%. Results showed that when reduced the media surface area to no media in anaerobic filter, 0.5 day anaerobic filter still had COD removal rate of 692.22 mg-COD/l-day, and plastic media in anaerobic filter could increase the COD removal rate at 122.84 mg-COD/l-m2-day. In addition, sand biofilter could percolate suspended solids from effluents of anaerobic filters to concentrations below disposal standard of 30 mg/L. Nitrate that were found in sand biofilter effluent suggested the change of anaerobic to aerobic condition and complete organic oxidation prior to nitrification process.