THE TREATMENT OF A HIGH-STRENGTH PULP AND PAPER-MILL EFFLUENT FOR WASTE-WATER REUSE - III) TERTIARY-TREATMENT OPTIONS FOR PULP AND PAPER-MILL WASTE-WATER TO ACHIEVE EFFLUENT RECYCLE

In an attempt to achieve water of a quality suitable for in-house re-u se, chemical coagulation, ozone and activated carbon adsorption were i nvestigated as options to remove both non-biodegradable COD and colour from the effluent of an activated sludge plant treating papermill was te water. Chemical coagulation was investigated using jartests and the results were scaled-up to a 6 m(3) hr(-1) pilot plant. This was able to remove 70% of the COD and 90% of colour using alum and it produced an effluent with a COD of 50 mg l(-1) and colour of 40 Pt-Co units. Oz one dosed at 60 mgO(3) l(-1) could remove 90% of the colour but had a poor COD reduction. Isotherm tests of activated carbon adsorption show ed a very high removal efficiency at 1.18 kg activated carbon m(-3) pr oduct, but this dosage incurred an excessive cost. Chemical coagulatio n followed by dissolved air flotation (DAF) and multimedia filtration proved the most suitable tertiary treatment process train. Operating c onditions were optimised for the chemicals applied, their dosages and the optimum pH. The process produced a medium grade recycled water sui table for reuse in the recycled fibre plant, and outline operating cos ts of producing this water were determined.