Biological treatment at low temperatures of sulfur-rich phenols containing oil shale ash leachate

Aerobic and sequential anaerobic-aerobic treatment of oil shale ash dump leachate (COD 2000–3000 mg l−1) was studied at 7–10° and at 20°C. The leachate was known to contain several phenolic compounds and have a high sulfur concentration. In the sequential anaerobic-aerobic processes, the chemical oxygen demand (COD) removals were most of the time slightly lower at 10°C (67%) than at 20°C (73%) while the biochemical oxygen demand for 7 days (BOD7) removals were 97–99% at both temperatures. In the anaerobic stages, the COD removal was a result of sulfide production. In the single aerobic process at 20°C, the COD removal was 65% while at 7°C the COD removal was 54%. After the feed was changed from leachate to phenol in the 7°C aerobic reactor, the COD removal stabilized to about 95%. In all the leachate treatment processes studied, the total phenols removals were on average 78–86%. The anaerobic stages removed total phenols minimally. An aerobic process at 7–20°C alone seems feasible for treating oil shale ash leachate.