DOMESTIC WASTE-WATER TREATMENT USING A UASB REACTOR

The performance of a pilot-scale (55-l) upflow sludge blanket (UASB) r eactor treating municipal sewage without any supplementary heating was examined in a 200-day trial. The flow rate to the digester was kept c onstant giving a hydraulic retention time of 7.6 h. Although there wer e some variations in the strength of the sewage, after the initial 18 days the loading rare was maintained at about 1.21 kg COD/m(3)day. A p regranulated sludge was used as the inoculum, bur the start-up period was still long; about 90 days. The total volatile fatty acid:alkalinit y ratio was initially high, indicating an element of instability in th e digester However; as more alkalinity was added to the incoming sewag e, the ratio fell below the critical value. Once this had been achieve d, the digestion process stabilised and achieved a COD removal efficie ncy averaging 85% and a specific gas yield of 0.34 m(3) methane/kg COD removed. (C) 1997 Elsevier Science Ltd.