Impact of land disposal of reject brine from desalination plants on soil and groundwater

The impact of reject brine chemical composition and disposal from inland desalination plants on soil and groundwater in the eastern region of Abu Dhabi Emirate, namely Al Wagan, Al Quaa and Um Al Zumool, was evaluated. Twenty five inland BWRO desalination plants (11 at Al Wagan, 12 at Al Quaa, and 2 at Um Al Zumool) have been investigated. The study indicated that average capacity of these plants varied between 26,400 G/d (99.93 m3/d) to 61,000 G/d (230.91 m3/d). The recovery rate varied from 60 to 70% and the reject brine accounted for about 30–40% of the total water production. The electrical conductivity of feed water and rejects brine varied from 4.61 to 14.70 and 12.90–30.30 (mS/cm), respectively. The reject brine is disposed directly into surface impoundment (unlined pits) in a permeable soil with low clay content, cation exchange capacity and organic matter content. The groundwater table 1ies at a depth of 100–150 m. The average distance between feed water intake and the disposal site is approximately 5 km. A survey has been conducted to gather basic information, determine the type of chemicals used, and determine if there is any current and previous monitoring program. The chemical compositions of the feed, product, reject, and pond water have been analyzed for major, minor and trace constituents. Most of the water samples (feed, product, reject and pond water) showed the presence of major, minor and trace constituents. Some of these constituents are above the Gulf Cooperation Council (GCC) and Abu-Dhabi National Oil Company (ADNOC) Standards for drinking water and effluents discharged into the desert. Total Petroleum Hydrocarbon (TPH) was also analyzed and found to be present, even in product water samples, in amount that exceed the GCC standards for organic chemical constituents in drinking water (0.01 mg/l).

The following points could be drawn from the study: 1. Seawater and brackish groundwater are considered as strategic alternatives to provide fresh water resources in the UAE and the Gulf countries. 2. Almost 98% of water supplies in the UAE are currently satisfied by seawater and brackish water desalination. 3. Considering the increase in desalination technology, attention must be given to evaluate desalination from environmental, technical and economical prospective. 4. Considering the geological nature of the study area, concentrate disposal to B2 B3 B2 B3 A1 4 A1 Ao Ao A2 A2 A3 A3 B2 B2 4 A1 Ao B1 4 B1 6 (A) Potassium B2 4 A1 Ao B3 A3 (B) Sodium B3 A2 B1 4 B1 6 B3 B3 A2 A3 31.5 24.5 17.5 10.5 3.5 B2 4 A1 Ao A2 A3 4 B1 6 (C) M agnesium B1 (D) Calcium Fig. 18. Cation distribution in subsurface soil below the disposal site at an average depth of 1.0 m.