Whey arising from cheese and casein manufacture has a BOD of 35-45 kg m-3 and must be treated prior to disposal. Bioconversion of lactose in whey to ethanol, yeast biomass or methane has been used to produce saleable products whilst reducing the organic load by greater than 75%. Higher BOD reductions can be achieved by combined processes, such as methane production from whey distillery effluents, but in most cases some aerobic treatment prior to final disposal is also required. The economics of such bioconversions can be favourable but market opportunities for other products and the demands of whey processing have limited the adoption of these technologies by the dairy industry.