Improved Biological Treatment Through Chemical Pre-Treatment, 2000 Environmental Conference Proceedings

- A. Roux, V. J. Bohmer -- Laboratory and pilot plant investigations were conducted into the removal of colour, recalcitrant organic material and bio-inhibitory compounds from Kraft effluents. This included precipitation of coloured organic material with lime or nitric acid followed by 2-stage biological treatment. Precipitation with lime removed a bigger range of colour compounds, but was difficult to control, required long reaction times, had high neutralisation requirements and the precipitate was difficult to separate. The increased soluble calcium in the effluent would limit the re-use of the treated effluent. Precipitation with nitric acid removed mainly lignin-derived organic material, was very easy to control, reaction time required was short, had low neutralisation requirements and counter ions were removed by biological treatment. Bio-inhibition was reduced with pretreatment with acid. The use of nitrate as nutrient for biological treatment did not reduce the efficiency of biological removal of organic material.