The Treatment of a High Strength Pulp and Paper Mill Effluent for Wastewater Re-Use

Abstract

In an attempt to achieve water of a quality suitable for in-house re-use, chemical coagulation, ozone and activated carbon adsorption were investigated as options to remove both non-biodegradable COD and colour from the effluent of an activated sludge plant treating papermill waste water. Chemical coagulation was investigated using jartests and the results were scaled-up to a 6 m³ 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. Ozone dosed at 60 mgO₃ l⁻¹ could remove 90% of the colour but had a poor COD reduction. Isotherm tests of activated carbon adsorption showed a very high removal efficiency at 1.18 kg activated carbon m⁻³ product, but this dosage incurred an excessive cost. Chemical coagulation followed by dissolved air flotation (DAF) and multimedia filtration proved the most suitable tertiary treatment process train. Operating conditions were optimised for the chemicals applied, their dosages and the optimum pH. The process produced a medium grade recycled water suitable for re-use in the recycled fibre plant, and outline operating costs of producing this water were determined.