Pilot-scale alkali-surfactant-polymer flooding produced water treatment system: performance and microbial community analysis

This study addressed the challenges of treating Alkaline-Surfactant-Polymer (ASP) flooding produced water by designing and implementing a pilot-scale advanced treatment process. The treatment train comprised a natural settling tank, a bioreactor, a dissolved air flotation (DAF) unit, and multi-stage filtration tanks. The system demonstrated a treatment capacity of 5 m³/h for ASP flooding produced water. The integrated process effectively removed oil content, suspended solids, and organic pollutants from the produced water. Experimental results revealed that the microbial reactor achieved removal rates of 95.36 % for oil content and 62.74 % for suspended solids. Subsequent three-stage filtration enhanced effluent quality to meet the stringent water reinjection standards for low-permeability reservoirs in Daqing Oilfield's polymer flooding produced water. This study comprehensively analyzed microbial community composition and structural changes within the bioreactor, identifying dominant bacterial species across different functional zones and elucidating their roles in pollutant degradation. With an operational cost of 1.15 CNY/m³, the proposed process demonstrates superior economic viability and environmental sustainability compared to conventional physicochemical processes. The advanced treatment process proposed in this study provides a novel technical approach to ensure stable compliance with standards and development requirements for ASP flooding produced water quality.