Efficiency and microbial community characteristics of strong alkali ASP flooding produced water treated by composite biofilm system

Strong alkali alkali-surfactant-polymer (ASP) flooding produced water is a by-product of oil recovery, and it is a stable system composed of petroleum, polyacrylamide, surfactant, and inorganic salts. Efficient, green, and safe ASP produced water treatment technology is essential for oilfield exploitation and environmental protection. In this study, an anaerobic/anoxic/moving bed biofilm reactor with a microfiltration membrane was established and assessed for the real strong alkali ASP flooding produced water (pH 10.1-10.4) treatment. The results show that the average removal rates of COD, petroleum, suspended solids, polymers and surfactants in this process are 57, 99, 66, 40, and 44%, respectively. GC-MS results show that most of the organic compounds such as alkanes and olefins in the strong alkali ASP produced water are degraded. Microfiltration membrane can significantly improve the efficiency and stability of sewage treatment system. Paracoccus (AN), Synergistaceae (ANO) and Trichococcus (MBBR) are the main microorganisms involved in the degradation of pollutants. This study reveals the potential and adaptability of composite biofilm system in treating the produced water of strong alkali ASP produced water.

[Characterization of microbial community in produced water from a petroleum reservoir subjected to alkali-surfactant-polymer ASP flooding]

Injection of alkali, surfactant and polymer (ASP) into oil reservoir can substantially increase oil recovery compared with water-flooding strategy. However, the effects of these agents on the microbial diversity and community structure, which is important for water management and corrosion control in oil industry, are hitherto poorly understood. Here, we disclosed the microbial diversity and community structure in the produced water collected from four producing wells of an ASP-flooded oilfield at Daqing, China, using high-throughput sequencing technique. Results showed that the average pH in produced water was as high as 9.65. The microbial diversity varied from well to well, and the Shannon diversity index was between 2.00 to 3.56. The Proteobacteria (85.5%-98.3%), γ-proteobacteria (83.7%-97.8%), and alkaliphilic Nitrincola (51.8%-82.5%) were the most dominant phylogenetic taxa at the phylum, class, and genus levels, respectively. A total of 12 potentially sulfide-producing genera were detected, and the most abundant taxon was Sulfurospirillum (0.4%-7.4%). The microbial community of ASP-flooded petroleum reservoir was distinct, showing an alkaliphilic or alkalitolerant potential; a reduced diversity and more simple structure were observed compared with those of the water-flooded petroleum reservoirs that were previously reported.