This paper examines the operation parameters and treatment efficiency in septage processing. The septage originated from septic ranks sewing non-sewered areas in Taichung City. An 8-l lab-scale digester,vas operated at ambient temperatures at solids retention times of 30, 20, 15, 10 and 5.3 days. The digester tvas fed once a day. The digester successfully operated at all the tested SRTs, but the highest efficiency was observed at SRT 10 days, organic loading 464 g COD/m(3)-day (chemical oxygen demand), or volatile solids (VS) loaning 1.462 kg/m(3)-day, with a COD removal efficiency of 80.4% and 30% VS reduction. Under this optimal operating condition, the removal rates of COD, NH3-N and total phosphorus were 373, 26.1 and 0.7 g/m(3)-day, respectively. The fraction of non-degradable VS to total VS was as high as 42.2% and the rate coefficient, K-b, for degradable VS destruction was 0.132/day.