During Phase I anaerobic filters were operated at mesophilic and thermophilic temperatures with hydraulic retention times (HRTs) of 12, 24, and 48 hours at chemical oxygen demand (COD) loads ranging from 2.75 g/L/day to 49.5 g/L/day (172 to 3090 lb/1000 cu ft/day). The purpose of the research was to determine the effect of HRT and organic (COD) loading as independent variables;Results indicated that the mesophilic systems were more sensitive to HRT than were the thermophilic systems with significant decreases in performance of the mesophilic systems with decreases in HRT. The thermophilic reactors showed virtually no reduction in performance with decreased HRT. The increase in organic load produced a reduction in removal efficiency at all HRTs for the mesophilic reactors. The effect of organic load was more significant at lower HRTs for the mesophilic reactors;The thermophilic units, on the other hand, displayed a reduction in COD removal only at the high COD loadings at an HRT of 48 hours. The increase in loadings showed little effect at the lower HRTs (24 and 12 hr) when the systems were able to flush inhibitory substances from the reactor. Overall, the thermophilic systems were able to treat the waste at more than twice the COD loading of the mesophilic systems;Phase II of the research involved initial studies on a two-temperature treatment system using a thermophilic anaerobic filter followed by a mesophilic anaerobic filter. The results showed improved removal efficiencies over the individual thermophilic or mesophilic systems operated at the same HRTs and organic loadings. Although further research is needed, these preliminary results indicate that two-temperature systems may be preferable to single temperature systems in some applications.