Constructing Wetlands in the Desert: An Example of Sustainable Produced Water Management in Oman

Abstract

Abstract Large volumes of produced water are generated as an associated co-product of oil production in Oman and other countries; the management of which often imposes a limitation on oil production. In many cases, a portion of this water is re-injected into reservoirs to maintain pressure for the oil wells. The remaining volume is typically disposed of into shallow aquifers or via Deep Well Disposal (DWD) which are environmentally undesirable and operationally energy intensive. Constructed wetlands represent an alternative option for treating produced water and have been trialled in Oman since 2000 with large-scale implementation since 2010. Wetland technology is a phytoremediation process in which native wetland plants facilitate microbial degradation of hydrocarbons. Volume reduction is also achieved through the high evapotranspiration rate of the plants. The advantages of wetland technology include: no or low-energy requirement, low operating cost, no chemical inputs, long life expectancy, high-level treatment performance & reliability. Based on these advantages, Petroleum Development Oman (PDO) decided to proceed with a large-scale application of wetland technology for management of produced water in its Nimr oil field in southern Oman. In 2008, BAUER was awarded a Design, Build-Own, Operate and Transfer (DBOOT) contract to develop the Nimr Water Treatment Plant (NWTP), which was commissioned in 2010. The capacity of the NWTP has been expanded over time and now has a capacity to treat 115,000 m3/day of produced water within 350 ha of Surface Flow Constructed Wetlands (SFCWs,) followed by 500 Ha of evaporation ponds (EP) for volume reduction and salt production. The entire process operates via gravity without any pumps. The inlet produced water is brackish (TDS 7,000 mg/L) and oil-in-water is 400 mg/L on average. More than 90% of the oil (260 bbl/day) is recovered at the front-end of the system using hydrocyclones and skimmers. The remaining hydrocarbons are biologically degraded within the wetlands, producing an effluent with oil-in-water below detection (< 0.1 mg oil/L) and brackish salinity (approximately 10000 mg/L TDS). Research and field trials are currently underway to develop options for reusing the wetland-treated water for irrigation of salt tolerant plants (biosaline agriculture) in order to produce biomass, bio-fuels, fibre and other products. The project has effectively created an "oasis" in the desert, providing valuable habitat for bird life (> 117 species identified at the site).