Biological treatment of petroleum produced water ex situ using microorganisms: an overview, main developments and challenges

摘要

Large volumes of a potentially polluting effluent are generated during oil extraction, denominated production water or produced water (PW). PW is characterised by high concentrations of contaminants, such as COD, nitrogen and phosphorus, heavy metals, hydrocarbons and others. This review aims to analyse ex situ biological treatment methods using microorganisms for PW. There are several consolidated physical and chemical treatments of PW. However, they present high operation costs and may raise the final value of the product. Thus, the biological treatment of PW performed ex situ by microorganisms has been the goal of research in recent decades, in order to develop an efficient and less costly process when compared to conventional treatments, resulting in microbial biomass and clean water. Ex situ biological treatment by microorganisms is carried out in acclimated bioreactors, with environmental (salinity, pH, temperature and light intensity (for microalgae)), nutritional (macro and micronutrients, and contaminants concentration to avoid nutrient limitation or substrate inhibition, mainly caused by hydrocarbons) and operating adaptations (type of bioreactor, class of microorganisms, treatment time and mode of operation (batch or continuous)) to maximize the treatment performance, which is promising reaching high removal rates of total oil and greases, nitrogen, phosphorus, metals and other contaminants. Bacteria are the most applied microorganisms even though microalgae, yeasts and filamentous fungi be tested in the last decade. Advantages and limitations of each class of microorganisms are presented in this review, and more research and technological development are expected in the future for this research topic.