Treatment of oilfield produced water by waste stabilization ponds: Biodegradation of petroleum-derived materials

This study evaluated the biological treatability of produced water (PW), the water separated from oil at the wellhead which contains both dispersed oil and low levels of heavy metals, using waste stabilisation ponds (WSPs). We examined both chemical oxygen demand (COD) and oil and grease (O&G) removal using different process configurations (hydraulic retention time (HRT), aerobic and anaerobic conditions, oil skimming, effluent recycle) in a small (10 L) reactor being fed a synthetic PW (COD = 1050-1350 mg L−1, O&G = 400-500 μL L−1, 6 gNaCl/L). The reactor was operated for 6 months, and at a HRT of 6 days (8 with evaporation) COD removals were greater than 85%, and improved over time to >90%, while O&G removals (measured with a newly developed method) were greater than 82% and also improved with time. Operating with an anaerobic section, oil skimming and 300% recycling were all found to enhance COD removal.