Primary Treatment of Municipal Wastewater in High- Rate Anaerobic Filter at Low Temperatures

The primary treatment of municipal wastewater was investigated in three high-rate anaerobic filter (AF) reactors operated in parallel at different hydraulic retention time (HRT) of 0.5, 1 and 1.5 h at low ambient temperature (average = 13°C). The media in each reactor consisted of vertical sheets of reticulated-polyurethane foam (RPF) with knobs. The results demonstrated that the AF reactor was an effective system for suspended solids (SS) removal. Total chemical oxygen demand (CODt) and suspended COD (CODss) removal efficiencies were 31 and 58%, respectively, at HRT of 1.0 h and were 40 and 67 %, respectively, at HRT of 1.5 h. The vertical orientation of RPF sheets with knobs and the presence of all biomass, only, in attached form in the AF reactors prevented reactors clogging. Therefore, the head losses were limited in the reactors (0.05 to 0.07 m). In addition to SS removal in the AF reactor, 8-15 % removal efficiency of dissolved COD (CODdis) was obtained and a partial anaerobic-digestion was achieved for the removed SS in the reactors. Moreover, the excess sludge from the AF reactor had a good settlability and filterability, as the sludge volume index (SVI) and filterability constant were 44 – 45 ml/g TS and 21x10 24x10 kg.m/s, respectively.