S. Ebrahim

Cleaning and regeneration of membranes in desalination and wastewater applications: State-of-the-art

Abstract Membrane fouling is a major problem in brackish and seawater desalination and in wastewater reclamation by reverse osmosis processes. Proper pretreatment and periodic cleaning and regeneration are the only available and widely used solutions for this problem. A critical review of methods of cleaning and regeneration of brackish water, seawater, and wastewater reverse osmosis membranes is presented. The review covers physical, chemical and physio-chemical cleaning methods, in addition to the regeneration of reverse osmosis (RO) membranes. Recent developments in cleaning and regeneration techniques and areas of research are also discussed.

Fifteen years of R&D program in seawater desalination at KISR. Part I. Pretreatment technologies for RO systems

Abstract Reverse osmosis (RO) has been established as a reliable process for seawater desalination. The reliability of the RO technique depends upon the extent of the pretreatment that must be designed to reduce the suspended and colloidal materials in the feedwater. During the last 15 years of research and development work at the Doha Research Plant (DRP), the Kuwait Institute for Scientific Research (KISR) has evaluated various types of pretreatment technologies for RO systems. These included: conventional pretreatment (CP), microfiltration (MF) and the beachwell (BW) intake systems. This paper gives brief description of these pretreatment technologies which were implemented at DRP and discusses their performances

System identification and control of reverse osmosis desalination

Abstract Efficient control system is the key point to a successful long-term operation in any industry. In reverse osmosis desalination process, various important parameters such as permeates flux and conductivity must be controlled. In this paper, the latest state of the art techniques are utilized to develop an effective closed loop control system for the above two mentioned parameters in a hollow fine fiber membrane configuration system located at the R&D laboratory at Doha Reverse Osmosis Plant of Kuwait. These techniques include: system identification, relative gain array and controllability test to find best pairings and structure, Zeigler-Nichlos settings to design SISO controllers for open loop systems, and for the multivariable system the biggest log modulus tunning technique is implemented. The manipulated variables are feed pressure and pH which control permeate flux and conductivity, respectively. The control system was simulated and satisfactory performance was obtained for set point tracking.

Economics of seawater desalination by reverse osmosis

Abstract The ultimate goal in the scientific study of desalting and water purification is to design a process that produces potable water at the lowest possible cost. Presently two major techniques are commercially used in different parts of the world: distillation and membrane processes. The dominant distillation process is multi-stage flash (MSF), and the main membrane process is reverse osmosis (RO). Although cost factors vary by site, the total cost of producing potable water from seawater with the RO process is usually less than thermal desalting processes. In this paper results of a study carried out in Kuwait to compare the unit cost of water produced from one-stage and two-stage hollow fiber (HF) and spiral wound (SW) seawater RO systems are presented. Results indicate that an average reduction in product water cost of about 22% could be achieved when one-stage RO is used instead of two-stage RO to produce drinking water from seawater in Kuwait. Moreover, an average of 11.84% of the capital investment cost can be saved by using a one-stage instead of a two-stage RO system. A greater reduction in product water cost is expected in the future as there is more room for improvement in the design, operation and maintenance of seawater desalination by RO technology.

Performance evaluation of two RO membrane configurations in a MSF/RO hybrid system

Abstract Although integration between multistage flash distillation (MSF) and reverse osmosis (RO) in hybrid desalination systems has been long discussed in the literature, and has been shown to be technically and economically superior to nonintegrated MSF and RO systems, no serious attempts have yet been made to adopt or implement such an approach in the design or construction of new desalination plants. This, perhaps to some extent, may be attributed to the real need first for some tangible experience on an acceptable scale and to the lack of experimental data on the performance of RO membranes in MSF/RO hybrid systems. Hence, this paper attempts to fill in this gap by presenting: operational experience using reasonably-sized RO production plants, a large body of experimental data on RO membrane performance in a simple MSF/RO hybrid model, and an overall evaluation of the performance of the RO membranes operating under the given conditions. The work represents the second phase of an experimental investigation of MSF/RO hybrid systems. In this phase the performances of two types of RO membranes operating in a simple easy-to-implement MSF/RO hybrid model were measured and evaluated. The experiments were carried out at the Doha Desalination Research Plant (DRP) using two RO units linked with the nearby MSF unit A-1 of the Doha East Distillation Plant via one common feed water header and pretreatment unt. The common feed water system, however, does not prevent either of the two RO units from being operated independently from each other. The RO units are of the spiral-wound and the hollow-fiber twin seawater RO membrane configurations, each of 300 m3/d nominal production capacity. Descriptions of the MSF/pretreatment/RO experimental model, measurements of performance data, analytical procedures, and discussions of the results obtained are presented. The results indicate that the two tested types of membranes behave in a very similar fashion, both qualitatively and quantitatively. RO product water recovery under hybrid operation is significantly higher than under isolated surface seawater operation. Up to a 43% increase in the RO product water recovery was realized when data under hybrid operation were compared with those under isolated surface seawater operation and similar feed pressures. The average change in RO product water recovery was almost linearly related to the change in feed water temperature at an average rate of 2.2% 1° C change in feed water temperature.

Pilot study of MSFRO hybrid systems

Abstract Evaluation of the reverse osmosis (RO) process performance in an multistage/reverse osmosis ( MSF RO ) hybrid system is of particular interest due to the obvious advantages of hybrid desalination plants over isolated ones. Meaningful evaluation of the RO process performance in a hybrid model requires continuous monitoring of an RO test unit for an appreciable period of time during the winter season when the ambient seawater temperature is low. The primary objective of this study was to systematically confirm possible gains in the RO product water flow rate and to examine the overall performance of an RO plant operating in a hybrid environment. Experiments were carried out at the Doha Desalination Research Plant (DRP) using a carefully designed and equipped 20 m3/d RO test unit linked with the nearby MSF unit A-1 of the Doha East Distillation Plant. Actual hybrid testing of the RO unit started during the cold season and continued for about 1,800 h. The temperature of the RO seawater feed withdrawn from the MSF reject stream ranged from 24 to 31°C. Operating data collected from the RO test unit included temperature, pressure, flow rate, concentration, silt density index (SDI), and pH according to the function of each stream. A description of the experimental model, including the MSF RO arrangement, performance data, and a discussion of the results obtained are included in the course of this paper. It was shown that an increase of up to 49% in the RO product water recovery was realized when data from before and after hybridization were compared. Also, a 42–48% gain in RO product water recovery was estimated for a seawater feed temperature of 33°C as compared to an isolated RO plant using surface seawater at a temperature of 15°C and at a reference feed pressure of 55 bar. Higher SDI values, increased frequency of backwash and chemical dosing, and loss of the membranes salt rejection were also encountered during the hybrid testing.

Desalting of subsurface water using spiral-wound reverse osmosis (RO) system: technical and economic assessment

Abstract Subsurface water rise is a major problem in Kuwait. The impact of this problem is manifested in surface water ponds, cracks in buildings, flooded basements and damaged roads. Dewatering this water of moderate salinity is necessary. Being in an arid area with very limited water resources, treatment and recycling of the subsurface water could be very important to a country like Kuwait. For this purpose, a pilot study was carried out by KISR to desalinate the subsurface water using the reverse osmosis (RO) technique. The main aim of this study is to assess the viability and economic feasibility of using RO technology. This paper outlines the results of over 8000 operating hours performance data of an RO plant utilizing spiral-wound membranes (SW) used to desalinate subsurface water with TDS of about 11,000 mg/1 and an economic feasibility evaluation. Results indicate that the (SW) RO system is a viable technique to desalinate this type of water. The improvements in TDS, COD and BOD were 99%, 96% and 42%, respectively. The economic feasibility evaluation indicates that the unit cost of desalting subsurface water by RO is 0.235 KD/m3 (0.776 US

Fifteen years of R&D program in seawater desalination at KISR part II. RO system performance

/m3), which is considered to be economically feasible for a small-scale plant.

Evaluation of commercial cleaning agents for sea-water reverse osmosis membranes

Kuwait Institute for Scientific Research (KISR) and the Ministry of Electricity and Water (MEW) collaborated over the past 15 years in developing and adapting the seawater reverse osmosis (RO) technology to the Gulf seawater conditions (one and half time the salinity of open seas and large temperature variations between summer and winter in the range of 35°C and 10°C, respectively). The development process went through several stages involving performance evaluation of three types of membrane configurations under various operating conditions and using different types of feed water pretreatment techniques. It went also through the evaluation of various commercially available energy recovery systems and the development of a new system. During this period, the RO research program evaluated the performance of ten different seawater membranes, cleaning and restoration techniques and procedures, using various potential agents. Furthermore, computer aided design program and process design and optimization procedures were developed specifically for Gulf seawater conditions. The studies also involved two-phase evaluation of multistage flash/reverse osmosis (MSF/RO) hybrid systems. Cost assessment of product water from RO under different operating conditions and various system configurations was always an important integrated part of each research project.

Microfiltration system as a pretreatment for RO units: Technical and economic assessment

Abstract In this work attempts were made to evaluate commercial seawater reverse osmosis (RO) membrane cleaning agents against the membrane manufacturers recommended cleaning agents. Results indicate that the commercial cleaning agents used in this study are generally more effective in restoring the performance of fouled membrane than the conventional cleaning agents recommended by the membranes, manufacturers.