Comparison of Membrane Pretreatment Options for Swro Operation

Comparison of Membrane Pretreatment Options for SWRO Operation

For Poster Presentation

R.R. Ferlita, R.C. Eck, X. Wang, G. Kim, and H. Roh

Russell Ferlita, Research Engineer (rferlita@doosanhydro.com), Research and Development, Doosan Hydro Technology, 912 Chad Lane, Tampa, FL 33619, USA, phone# 813-805-8859, fax# 813-623-6666

Ryan Eck, Research Engineer (reck@doosanhydro.com), Research and Development, Doosan Hydro Technology, 912 Chad Lane, Tampa, FL 33619, USA, phone# 813-805-8404, fax# 813-623-6666

Xing Wang, Research Engineer (xwang@doosanhydro.com), Research and Development, Doosan Hydro Technology, 912 Chad Lane, Tampa, FL 33619, USA, phone# 813-805-8384, fax# 813-623-6666

Gyu Dong Kim, Research Engineer (gkim@doosanhydro.com), Research and Development, Doosan Hydro Technology, 912 Chad Lane, Tampa, FL 33619, USA, phone# 813-805-8778, fax# 813-623-6666

Hyung Keun Roh, Director of Research and Development (hroh@doosanhydro.com), Research and Development, Doosan Hydro Technology, 912 Chad Lane, Tampa, FL 33619, USA, phone# 813-805-8383, fax# 813-623-6666

Abstract

The increased pressure on the current water resources is a direct result of the increasing water demand and climatic drought conditions in many areas of the world. To meet these demands, many utilities must diversify their water supply portfolio to maintain required production of clean water. This has led to the use of nontraditional water sources with relatively high levels of contaminants, such as the sea (1-6).  Among the leading technologies implemented for desalination is seawater reverse osmosis (SWRO).  SWRO systems are sensitive to the quality of water delivered to them.  High quality feed water is desirable; however, the capital expenditure (CAPEX) and operational expenditure (OPEX) of the system must be taken into consideration when designing and building an SWRO treatment plant.  Two different membrane pretreatment types [both ultrafiltration (UF) and microfiltration (MF)] and a total of six different modules were compared to each other on the basis of overall costs, energy and chemical requirements. In addition, the quality of water delivered to the SWRO system was compared between UF and MF.

Due to the nature of the membrane filter operation, frequent backwashes and chemical cleanings are necessary to maintain good performance and prevent irreversible fouling.  Due to these factors, membrane pretreatment is often perceived as being a more expensive option. However, the high filtrate quality obtained from membrane filtration allows for increased flux operation of RO membranes, decreasing the CAPEX and OPEX of the RO system.  The filtrate generated from the membrane pretreatment systems in this study was fed to an SWRO system.

The investigation of the membrane pretreatment system was undertaken in two separate parts.  The first part was the investigation of three different UF membranes (designated membranes 1, 2, and 3) using inside-out filtration mechanism.  These membranes characteristically had a small pore size (approximately 0.02µm).  The second part of the membrane pretreatment investigation incorporated three different MF membranes (designated membranes A, B, and C) using outside-in filtration mechanism.  The pore size of these membranes was approximately 0.1µm.  The operation of all the membranes tested was performed according to manufacturers’ recommendations and was optimized for the water quality tested. The filtrate quality delivered by the membrane pretreatment system was consistently high (turbidity <0.05 NTU and SDI<3), regardless of the feed water quality.  This reliable performance is due to the absolute barrier provided by the membranes.  Since no coagulation was used for all the pretreatment membranes tested, no significant removal of dissolved organic carbon was observed.

In order to evaluate the relative performance of the membrane types and models tested and their effects on the operation and performance on downstream membrane desalination processes, an SWRO system was constructed. In order to effectively compare the membrane pretreatment systems, operational parameters and performance of the SWRO system were monitored.  Additionally, membrane elements from two manufacturers were tested (designated membrane α and membrane β for comparison) and their operational conditions were optimized using projection software provided by the manufacturers.

The results of this study indicated the SWRO system fed with filtrate from the UF pretreatment system consistently operated at lower pressures and consumed less energy than the SWRO system fed with filtrate from the MF system. Additionally, the performance of the SWRO system was more stable (suffered from less fouling). Membrane pretreatment is considered to have a number of benefits when compared with conventional pretreatment options, such as Dual Media Filtration. However, the pore size plays an important role in fouling of RO membranes. Thus, a detailed analysis of membrane performance under various membrane pore sizes is needed.

Keywords

SWRO, membrane pretreatment, membrane comparison

References

(1) Fritzmann, C., et al., State-of-the-art of reverse osmosis desalination. Desalination, 2007. 216(1-3): p. 1-76.

(2) Greenlee, L.F., et al., Reverse osmosis desalination: Water sources, technology, and today's challenges. Water Research, 2009. 43(9): p. 2317-2348.

(3) Jacangelo, J.G., R. Rhodes Trussell, and M. Watson, Role of membrane technology in drinking water treatment in the United States. Desalination, 1997. 113(2-3): p. 119-127.

(4) Shannon, M.A., et al., Science and technology for water purification in the coming decades. Nature, 2008. 452(7185): p. 301-310.

(5) Van der Bruggen, B. and C. Vandecasteele, Removal of pollutants from surface water and groundwater by nanofiltration: overview of possible applications in the drinking water industry. Environmental Pollution, 2003. 122(3): p. 435-445.

(6) Van Der Bruggen, B., et al., A review of pressure-driven membrane processes in wastewater treatment and drinking water production. American Institute of Chemical Engineers, 2003. p. 46-56.

(7) Wilf, M. and C. Bartels, Optimization of seawater RO systems design. Desalination, 2005. 173(1): p. 112.