Dairy wastes are generally dilutions of milk or milk products, together with detergents, sanitizers, lubricants, chemicals from boiler and washings from tank trucks. The strength of the waste varies very widely. In the United States and New Zealand, the chemical oxygen demand (COD) of the dairy plant wastes is said to vary in the range of 80-95,000 mg/L and 180-23,000 mg/L respectively,' although 4,000 mg/L is the typical ~ t r eng th .~ The mean COD of the effluent of a dairy plant in Canada was reported to be 3390 m g / ~ . ~ Only limited information is available on the performance of the anaerobic filters in treating dairy wastewater at low temperatures. In this context, it was proposed to study the performance of anaerobic filters treating dairy wastewater operating at 10-20°C and compare this performance with anaerobic filters operating at 30-35°C.