TREATMENT OF OILFIELD PRODUCED WATER USING A PILOT-SCALE CONSTRUCTED WETLAND TREATMENT SYSTEM

In recent years production of oil in sub-Saharan Africa has generated thousands of barrels of oilfield produced water (OPW). If water produced from oilfields in sub-Saharan Africa can be treated, this large volume of water has the potential for use in irrigation, which could decrease demand on existing water resources. In this investigation a pilot-scale constructed wetland treatment system (CWTS) consisting of three series: a free water surface flow (FWS) series, a subsurface flow (SSF) series, and a hybrid SSF series preceded by an oil-water separator (OWS), was utilized to treat OPW. Two major objectives were to: 1) assess treatment performance of a pilot-scale CWTS at different mass loadings of O & G, and 2) determine effects of a specific OPW on seed germination and early seedling growth after treatment in a pilot-scale CWTS. Concentrations of O & G and metals in simulated OPW decreased during treatment in both the SSF and FWS series for all mass loadings of O & G (5, 10, and 20 mg/min). Development of reducing conditions as mass loading of O & G was increased enhanced the removal of nickel and zinc from OPW. Removal of O & G, which is favored by oxidizing conditions, was greater for low O & G loadings compared to high O & G loadings in the SSF and FWS series. Removal of manganese was greater at low O & G loadings in both series, and iron removal was greater at low O & G loadings in the FWS series. The SSF series with an OWS demonstrated greater removal of O & G compared to the SSF series without an OWS. Seed germination and early seedling growth bioassays revealed that phytotoxicity was greater in untreated OPW compared to treated OPW. Probable sources of phytotoxicity were metals in test water and nutrient deficiencies in growth substrate. Results indicate the following sensitivity scale for plant species in order from most sensitive to least sensitive: lettuce \u3e soybean \u3e watermelon \u3e corn \u3e okra ∼ millet \u3e sorghum