Date of Award

2003

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. A.M.O. Mohamed

Second Advisor

Mohsen Sherif

Third Advisor

Djouida Chenaf

Abstract

The impact of reject brine chemical composition and disposal from inland desalination plants on soil in the eastern region of Abu Dhabi Emirate, namely Al Wagan, Al Quaa and Urn Al Zumool, was evaluated. Twenty five (25) inland Brackish Water Reverse Osmoses (BWRO) desalination plants (11 at Al Wagan, 12 at Al Quaa, and 2 at Urn Al Zumool) were investigated. The average capacity of these plants varied between 26,400 G/d (99.93 m3/d) and 61,000 G/d (230.91 m3/d). The recovery rate varied from 60 and 70% and the reject brine accounts 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 to 30.30 (mS/cm), respectively. The reject brine was disposed directly into surface impoundment (unlined pits) in a permeable soil with a low clay content, a cation exchange capacity (CEC) and organic matter content. The groundwater table lay at a depth of 100 - 150 m. The average distance between feed water intake and the disposal site was approximately 5 km. A survey was conducted to gather basic information, to determine the type of chemicals used, and determine if there were any current and/or previous monitoring programs. The chemical compositions of the feed, product, reject, and pond water were 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 were above the Gulf Co-operation Council (GCC) and Abu-Dhabi National Oil Company (ADNOC) Standards for drinking water and effluents discharged into the desert. The Total Petroleum Hydrocarbon (TPH) was also analyzed and found to be present, even in product water samples, in amounts that exceeded the GCC standards for organic chemical constituents in drinking water (0.01 mg/l). Chemical analysis has revealed that the horizontal movement of contaminants was higher than the lateral movement. The fate, and impact of concentrate (reject brine), was studied using batch and column tests. The results obtained from the batch test revealed that the retardation coefficient takes the following order Potassium>Strontium>Sulfate. The results obtained from the leaching column test showed that strontium retardation calculated as the area under the curve and for PV at C/Co = 0.5 was higher for in-place (natural) soil than sand dune soil. In addition, the changes in electrical conductivity (EC) were similar to that of an ideal tracer. The outcomes from CXTFIT modeling program indicated that the in-place (natural) soil had a higher dispersion coefficient (D), a higher retardation coefficient (R) and a greater dispersivity (α) than sand dune soil. This suggested a faster movement of contaminants in sand dune. Predictions of field conditions using CXTFIT model showed that Sr required 13-14 days to reach the feeding aquifers of 100 m depth in the case of sand dune soil, whereas it requires 16 days for the In-place soil. Finally the available options that can be implemented to reduce the impact of reject brine on environment were discussed.

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