The manufacture of paper generates significant quantities of wastewater; as high as 60 m(3)/tonne of paper produced. The raw wastewaters from paper and board mills can be potentially very polluting. Indeed, a recent survey within the UK industry has found that their chemical oxygen demands can be as high as 11 000 mg/l. This paper reviews the processes involved in paper making and examines the effects which they could have on the environment. It also evaluates the treatment processes which are used to minimise these effects. In line with the majority of UK practice, it focuses mainly on aerobic biological treatment and, in particular, on the activated sludge process. This means that there is an in-depth discussion about the problems associated with filamentous bacteria and sludge "bulking". The paper also discusses the way in which anaerobic digestion can be applied to the treatment of liquid wastes from the manufacture of paper. (C) 2001 Elsevier Science Ltd. All rights reserved.