Start-up alternatives and performance of an UASB pilot plant treating diluted municipal wastewater at low temperature

Different start-up procedures of an upflow anaerobic sludge bed (UASB) digester were carried out. Start-up without inoculum (experiment A) was delayed for about 120 day. The digester reached 75–85% total suspended solids (TSS) removal, 54–58% total chemical oxygen demand (TCOD) removal and 63–73% biological oxygen demand (BOD5) removal at influent concentrations of 240–340 mg TCODi l−1, temperatures of 13.5–15 °C and hydraulic retention times (HRT) of 10–11 h. Digested sludge was used as inoculum in experiment B. After the start-up period of 75 days, digester efficiencies were 58%, 41% and 54% for TSS, TCOD and BOD5 removal, respectively, working at 169 mg TCODi l−1, temperature of 14 °C and HRT of 11 h. The sludge bed developed and stabilised quickly when using a hydraulically adapted inoculum (experiment C), but TCOD and BOD5 removals remained low and volatile fatty acids (VFA) accumulated in the effluent.