Treatment of produced water for dissolved oil and heavy metals: Methanogenic degradation coupled to dolomite filtration

Abstract:

Successful integration of vast volumes of produced water (PW) into industrial and agricultural uses constitutes an alternative to the growing scarcity of underground sources of drinking water (USDW). Technologically, this can be readily achieved by treating PW for salinity, heavy metals, and dissolved oil utilizing conventional chemical, biological, and physical water treatment technologies. However economically, the cost of treating PW by conventional water treatment technologies limits their utilization. For PW to be successfully integrated into industrial and agricultural uses, new economic technologies needed to be investigated.

Our preliminary experimental results indicate that pretreating PW by combining methanogenic degradation of dissolved oil (n-alkanes) and dolomite filtration of heavy metals (e.g., Ba) can enable the use of conventional water treatment technologies (e.g., membrane filtration) to remove remaining contaminants (e.g., NaCl, BTEX, PAHs) from PW at an economic cost. The technological novelty of the proposed pretreatment method is on (1) the use of anaerobic oil degrading microbial communities present in PW that are well adapted to high salinity conditions, and (2) the use of dolomites that represent a superior sorption capacity for heavy metals than other natural and inexpensive sorption materials (e.g., sandstone). The practical novelty of the proposed research is on (1) the feasibility of operating PW storage tanks as anaerobic bioreactors, and (2) the abundance and easy access to high purity dolomites in outcrops of the Arbuckle Group of Oklahoma and Kansas.

In this contribution, we introduce experimental results on (1) the stimulating effect of the combined supply of protein-rich matter and CO₂ on the methanogenic degradation of dissolved oil (n-alkanes) using PW collected from the Cushing and Stillwater oilfields, and (2) on the removal of barium from synthetic PW using compressed dolomite filters made of powdered dolomite collected from an outcrop in Kansas.