Possibilities for biotechnical in situ-remediation of groundwater contaminated sulphite pulp mill effluents

Biotechnical in situ-remediation of groundwater contaminated by sulphite pulp mill effluents was examined at laboratory scale. The contaminated groundwater and soil consisted mainly of organic substances dissolved from wood and formed during sulphite pulping. The contaminants consume oxygen in the groundwater. In situ-simulation with air-lift percolators and a semi-continuous reactor were performed in darkness at 9 °C. The highest DOC concentration was 8400 mg/1 and the average DOC reduction rate was 56.7 mg/d. The DOC reduction achieved was 13-17%. The effects of pH and the presence of the original soil material were studied. There was no significant difference in the performance of the percolators at the ambient (4.3-4.5) or adjusted (6.5-7.5) pH. Neither was the DOC reduction of the percolators containing the original soil material higher than the one containing only burned and washed sand. The possibility of maintaining a stable DOC reduction was studied with a semi-continuous reactor test. Average DOC reduction of 20 and 7.8% with hydraulic retention times of 7.6 and 1.6 days, respectively, were achieved.