A lab-scale investigation was conducted to examine the effectiveness of a multi-fed upflow anaerobic filter process for the methane production from a rice winery effluent at ambient temperatures. The experiment was carried in two identical 3.0-l upflow filters, a single-fed reactor and a multi-fed reactor. The results showed that the multi-fed reactor, operated at the ambient temperatures of 19-27 degrees C and influent chemical oxygen demand (COD) of 8.34-25.76 g/l, could remove over 82% of COD even at an organic loading rate (OLR) of 37.68 g-COD/l d and a short hydraulic retention time (HRT) of 8 h. This reactor produced biogas with a methane yield of 0.30-0.35 l-CH(4)/g-COD(removed). The multi-fed upflow anaerobic filter was proved to be more efficient than the single-fed reactor in terms of COD removal efficiency and stability against hydraulic loading shocks. A linear-regression model with influent COD concentration and HRT terms adequately described the multi-fed upflow anaerobic filter system for the treatment of rice winery wastewater at ambient temperatures. (c) 2006 Elsevier Ltd. All rights reserved.