Treatment of integrated newsprint mill wastewater in moving bed biofilm reactors

Wastewaters from three integrated newsprint mills have been treated in a pilot plant Moving Bed Biofilm Reactor (MBBR). In the MBBR the biomass adheres to small plastic elements which move freely along with the water in the reactor. A reduction of 65-75% for COD and 85-95% for BOD was obtained at HRT of 4-5 hours. By prolonging the HRT the removal efficiencies of COD and BOD increased to about 80% and 96%, respectively. With a subsequent chemical precipitation a removal efficiency of COD up to 95% was achieved. The amount of chemicals needed for precipitation of the biologically treated wastewater was only a quarter to a third of that needed for chemical treatment of the untreated wastewater. The results showed the MBBR process to be competitive with conventional biological treatment systems and that treatment objectives can be met at short HRTs.