Laboratory scale anaerobic digestion studies were carried out to determine the effect of high-shear mixing on the degradation of lipids. The studies showed that the intensity of mixing must be carefully tailored to the rate and type of feed if benefits are to be realized. Dog food, cottonseed oil, and motor oil were fed to the digesters daily as slug loads. When properly operated, the 15 replicate digesters gave reproducible results with good precision. High-shear mixing has little effect on degradation of dog food and was deleterious to lime-buffered solutions heavily loaded with cotton seed oil. When soda ash was used as a buffering agent, heavy loads of oil caused the digester to 'go sour' regardless of the mixing system. Under some conditions homogenization led to serious foaming in the digestors. Kinetic data and chemical analysis of drawdown samples confirmed the hypothesis that homogenization or soda ash buffering can accelerate the hydrolysis of a heavy load of fat to a point where the saponification products over load the methane fermentation. Motor oil was not readily digested but did not appear to influence the digestion of cottonseed oil or dog food. Other observations were: (1) more rapid gasification occurs as the feed rate increases; (2) lime and soda ash cannot be used interchangeably as buffers; and (3) feed COD cannot be used to predict methane yield. (Author)