Date of Award

6-2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Mohamed Abdulkarim,

Second Advisor

Dr. Sergei Agashichev

Third Advisor

Dr. Corrado Sommariva,

Abstract

In this thesis, a technological and economical comparison was conducted on both conventional and membrane based pre-treatment before reverse osmosis desalination. In order to produce high quality water at the design recovery ratio, reverse osmosis membranes should receive high quality feed water in terms of turbidity, suspended solids, and biological matters. Conventional pre-treatment schemes of media and cartridge filters after coagulation chambers have been used for years. Due to the poor performance and decline in reverse osmosis recovery, membrane based pre-treatment has emerged and has been under research and study in the recent years. Few conventional pre-treatment reverse osmosis plants have been replaced by a membrane based pre-treatment.

The following study is an attempt into that direction to state and verify the ability of membrane based pre-treatment scheme to produce the high quality feed water to the reveres osmosis membrane.

The methodology used for analysis of technological schemes includes three groups of technological and economic indicators, these are: (A) water quality data; (B) technological characteristics of equipment, and (C) economic characteristics of the processes.

The study is based on set of experimental projections of water quality data after pretreatment such as turbidity, the SDI index and total suspended solid. These data were received from several pilot system and full- scale plants. These plants are: (1) conventional pretreatment of the RO pilot plant installed by Ondeo Ltd. located at AI -Taweellah site, (2) conventional pretreatment installed at AI-Fujairah hybrid desalination plant, (3) MF pretreatment based on the "Zenon" system located on AI-Taweellah site, (4) UF pretreatment based on the "Aquasource" system located at AI-Taweellah site, (5) hybrid type of pretreatment proposed by GrahamTech Pte Ltd (Singapore) located in Bainouna power station, and (6) pretreatment scheme of RO desalination plant in Addur (Bahrain).

The average SDI15 index of filtrate over three months of study provided by the "Aquasource-UF and "Zenon-MF" systems were 1.5 and 2.9 respectively. Required level for reverse osmosis should not exceed an SDI15 of 3.0. Hybrid type pretreatment proposed by GrahamTech Pte Ltd demonstrated satisfactory level of performance characteristics. The SDI15 index observed to be less than 1.0 and daily degree of deterioration of normalized permeability was 0.27%. Comprehensive analysis for these case studies is explained in chapter 5.

Economic assessment of pretreatment schemes in design of the sea water RO was conducted on a demo plant. Design capacity of the demo plant is 250 m3(of permeate)/day. The design of the demo plant was prepared by Japan Cooperation Center for the Middle East. The project is part of the "Advanced Hybrid Desalination System in Abu Dhabi".

The following economic forecasts were done in this study: total cost of filtrate (including investment and O&M of pretreatment) is estimated to be 0.48 and 0.57 $/m3(fiItrate) for conventional and membrane pretreatment respectively. Cost of installed equipment is estimated to be 520.05 $/ m3/d and 613.6 $/ m3/d for conventional and membrane pretreatment respectively.

This study concludes that membrane-based pretreatment is a competitive technological alternative to conventional one. Membrane-based pretreatment can successfully coexist with conventional pretreatment rather than the process that should replace it. Some hybrid configuration of pretreatment schemes including conventional processes along with MF and UF can be recommended for further research.

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