Water treatment membranes, used extensively for desalination, are rapidly expanding into other markets, according to a recent Lux Research (www.luxresearchinc.com) report, including municipal water recycling, industrial process water and wastewater treatment, and cooling tower and boiler water treatment. In the report — “Filtering out growth prospects in the $1.5 billion membrane market” — Lux Research predicts the global market for water treatment membranes will almost double during the next decade from $1.5 billion in 2009 to $2.8 billion in 2020.
There are four primary types of water treatment membranes, said Joe Such, general manager of Reverse Osmosis and Electrodialysis Technology, GE Power & Water:
- Microfiltration (MF) removes what can be seen in the water, primarily total suspended solids (TSS). Applications include pretreatment of water for filtering with other membrane systems.
- Ultrafiltration (UF) removes the next smaller size of contaminants, including TSS and total dissolved solids (TDS). Applications include pretreatment to reverse osmosis systems.
- Nanofiltration (NF) removes even smaller particle sizes such as pesticides, herbicides, and synthetic dyes.
- Reverse Osmosis (RO) removes the smallest particle sizes such as acids, aqueous salts, and metals. Applications include boiler feedwater treatment, drinking water systems, and ingredient water for beverage production.
“Membrane systems are designed based on molecular size of the particle that needs to be separated from the water,” Such said. “Which membrane is used in an application is dependent on what is in the water and what quality the water needs to be.”
Russ Swerdfeger, product manager, Memcor UF Products, Siemens Water Technologies, further explained that MF and UF are hollow-fiber membranes that are most commonly used for solids removal processes. “The majority of the installed base in North America operates in ‘out-in’ mode (feed water passes from the outside of the fiber to the inside; filtrate is collected in the center of the fiber), with membrane pore sizes ranging from 0.01-0.2 microns,” he said. “MF/UF is used in municipal water systems as a final filtration step, in wastewater re-use applications filtering secondary effluent, pretreatment in seawater desalination, and industrial applications for process water make-up or pretreatment to RO.”
NF and RO are pressure-driven, spiral-wound membranes that remove dissolved contaminants. “However, they are susceptible to solids loading, making MF/UF excellent pretreatment options,” Swerdfeger said. “Typical applications include municipal drinking water for softening or desalination, wastewater polishing for re-use, and industrial process water make-up.”
Membrane bioreactor (MBR), another treatment process gaining acceptance, uses hollow-fiber or flat-sheet membranes, MF/UF processes, and also incorporates a biological reactor in wastewater treatment applications, Swerdfeger said. Most configurations operate in a submerged driven out-in mode.
There are a number of factors to consider when designing a water treatment system incorporating membranes. “In applying UF membrane systems, we first consider the capacity demands and treatment goals of the process to determine if a pressure or submerged process best suits the application,” Swerdfeger said. “We then focus on feed water quality and attempt to understand just how the owner needs the membranes to perform.”
According to Swerdfeger, designers need to understand the following:
- turbidity fluctuations of the feed;
- temperature range of the feed;
- total organic carbon;
- iron and manganese;
- alkalinity; and
“We also look at the process integration of the UF system,” Swerdfeger said. “For example, some sites lack wastewater disposal, in which case we must consider where backwash and cleaning wastes would end up. We encourage our customers to think in a system’s perspective, meaning, ‘let us work with you to help optimize the design and operations of the UF system in question.’”
GE Power & Water’s Such divided design considerations into three areas: project scoping details, make-up water quality details, and target product quality details. Project scoping details include determining flow rates, both daily and peak flow; identifying all water sources — well water, municipal supply, surface water, or process water/wastewater — and seasonal variations; and determining a projected running schedule (24/7 or on/off) and storage capabilities such as whether existing tanks are available for post-pretreatment break and for permeate product storage.
Make-up water quality details include the following:
- detailed feed water analysis;
- free and total chlorine analysis;
- Silt Density Index (SDI) for projected make-up water (SDI evaluates the potential of feed water to foul a 0.45-micron filter);
- turbidity for projected make-up water;
- particle size analysis for projected make-up water;
- temperature of feed water (average and range);
- Grid 48 for process water re-use applications;
- Argo Analyzer projections; and
- pretreatment and cleaning chemicals required.
Target product quality details include target product quality parameters and flows.
As water treatment membranes gain market share and find broader application, equipment manufacturers are responding to these trends with more efficient and integrated systems. “Speaking from the perspective of UF membranes only, we see demand for UF increasing globally,” Siemens’ Swerdfeger said. “Siemens maintains a robust research and development program that seeks to advance membrane fiber and UF module technology. Specifically, we see a trend toward the use of UF as pretreatment to RO in both advanced wastewater re-use and desalination applications.
“These applications are growing rapidly as water-stressed regions seek reliable alternative water supplies,” Swerdfeger said. “We are innovating in materials, component, and systems levels to address these applications and to improve our products for established applications such as surface water filtration. We expect the outputs of our membrane research and development will allow us to offer even more cost-effective and efficient UF systems in the future.”
GE Power & Water’s Such noted a water re-use trend. “Our advanced, reliable portfolio of chemicals, equipment, and services gives GE the ability to deliver a comprehensive, integrated approach to wastewater management, resulting in improved operational efficiency, enhanced life cycle value, and reduced environmental footprint,” he said.
GE’s Re-PAK system is an integrated UF and RO package plant designed for water re-use applications. The two technologies are combined on a single skid with a single control system and use a multifunctional tank for clean-in-place, break, and back-pulse functions, versus three tanks in a traditional UF/RO configuration, Such explained. This helps reduce Re-PAK’s footprint by 35 percent and optimizes equipment integration for efficient performance, he said.
Desalination research center opens
The hub of NCED will be a desalination pilot-scale testing and research facility, which will allow researchers to performance test new and improved desalination technologies and processes at a pilot scale, enabling the industry to validate commercial products, integrate currently available technology, and assess potential technology options. CH2M HILL was appointed lead design consultant for the new pilot-scale testing and research facility, which is expected to be operational by September 2011, in time for the International Desalination Association World Congress in Perth.