METHANOGENIC DEGRADATION OF DISSOLVED OIL HYDROCARBONS IN PETROLEUM PRODUCED WATER

Petroleum produced water (PW) is one of the most significant waste streams in the oil and gas industry. If treated for its high concentrations of dissolved salts and oil hydrocarbons, PW could be integrated into industrial and agricultural uses. One of the main factors impeding the use of conventional membrane filtration technologies to treat produced water is the high concentrations of dissolved oil hydrocarbons that causes severe fouling (plugging) problems in membrane filters. To reduce the cost of treating huge volumes of PW, we are studying a new treatment method that takes advantage of indigenous methanogenic oil-degrading microbial communities adapted to high salinity environments. The method consists of combining the supply of carbon dioxide and protein-rich matter (soy protein) to boost the activity of indigenous methanogenic oil-degrading microbial communities present in PW. Without extra expenditure, available water storage tanks may be used as anaerobic enclosed reactors. Soy protein constitutes the cheapest type of protein-rich matter in the world, and the produced methane could be recovered from the anaerobic enclosed tanks for subsequent purification and commercialization. Our vial experiments conducted to analyze the effect of temperature, oxidation reduction potential, and type of PW shows that the proposed stimulation method can lead to an 85% removal of typical concentrations of dissolved oil hydrocarbons (0.5-1.5 mg-oil/L) from PW within a couple of weeks. Oil hydrocarbons degradation by the proposed method is concomitant with methane production and carbon dioxide consumption, proving the synergetic effect of combining the supply of carbon dioxide and protein-rich matter to stimulate oil hydrocarbons degradation. Experiments were conducted using PW collected from the Cushing and Stillwater oilfields of Oklahoma. Salinity of the PW is an essential factor determining the feasibility of methanogenic degradation of dissolved oil hydrocarbons. We found that isolated soy protein can replace more expensive protein-rich matter such as yeast extract, especially when large quantities are required.