Constructed subsurface flow wetland for treating heavy oil-produced water of the Liaohe Oilfield in China

A pilot subsurface flow constructed wetland (CW) has been constructed in the Liaohe Delta, China to treat heavy oil-produced water with large amounts of dissolved recalcitrant organic compounds. Pollutant concentrations and change of wetland plants were periodically monitored. Treatment effectiveness was evaluated and indicated high mean removal efficiencies, 81% for chemical oxygen demand (COD), 89% for biochemical oxygen demand (BOD5), 89% for mineral oil, and 81% for total Kjeldahl nitrogen (TKN) achieved in reed bed #2, to produce wetland effluent average concentrations with COD 77 mg l(-1), BOD5 3.5 mg l(-1), TKN 2.2 mg l(-1), and mineral oil 2.9 mg l(-1). We observed that during the vegetation growth period there was no influence of heavy oil-produced water on the numbers of leaves of reeds in CW, whereas, the biomasses and heights of reeds showed significant loss with increasing hydraulic loading. The heavy oil-produced water had no obvious effect on the reed indices of cellulous, lignin, pentose and the length/width ratio of cellulose. (C) 2002 Elsevier Science B.V. All rights reserved.