Biological lagooning of phenols-containing oil shale ash heaps leachate

In the course of the present study the biological treatment of leachate from oil shale semicoke ash heaps in a wastewater lagoon was investigated. The lagooning process was simulated by laboratory-scale batch processes and a lagoon, by applying different aeration conditions at 20°C. Treatment in the lagoon significantly reduced chemical oxygen demand (COD), biochemical oxygen demand (BOD) and phenols in the leachate. A removal of 55–64% of COD was achieved. The removal of phenols, estimated on the basis of identified phenolic compounds, was 80–88%. The best removal of COD, up to 70%, was achieved in the intermittently aerated batch, while in the non-aerated batch the removal was 41%. In the intermittently aerated batch the removals of phenol, methylphenols and dimethylphenols were on the average from 95 to over 99%. All the tested systems showed lower removals of resorcinols compared to those of monohydric phenols. This study indicates that leachate from oil shale semicoke ash heaps could be treated in an aerated lagooning system, and that the biological treatment of the high pH leachate is feasible without pH adjustment.