The treatment of effluent from a paper/board factory that produced 280 tons of cardboard and consumed 1200 m(3) of water per day was carried out. Wastewater analysis showed that the mill effluent contained 3000 mg dm(-3) suspended solids, 1400 mg dm(-3) COD (chemical oxygen demand) and 500 mg dm(-3) BOD (biochemical oxygen demand). An internal treatment cycle is suggested that involves recirculation of paper-machine wastewater (white-water) and may be accomplished by installing a flotation saveall (fiber recovery) unit. This arrangement reduced fresh water use by about 90%, reduced fiber loss by 80-90%, and increased board production by 13%. An external treatment process for the effluent was assessed by conducting laboratory coagulation tests (alum, ferric chloride, ferrous sulfate, and polyelectrolyte) on the whole mill effluent. Oxidation of the mill effluent using calcium hypochlorite before discharging the effluent to a lagoon offers the benefits of killing the harmful bacteria and reducing the pollution load. (C) 2003 Society of Chemical Industry.