Membranes are changing the trajectory of wastewater treatment’s future. While they have been used for three decades, in the last 10 years high-quality membrane-based treatment for water reuse made rapid gains. More often than ever, membranes are incorporated into treatment plant upgrades or expansions.
"The larger trends driving growing use of membranes today are first, global advances in industrialization and technology, leading to increased water demands, including for higher purity water, and second, massive urbanization in emerging markets," said Erik Hanson, senior product manager, filters and membranes, for GE Power Water and Process Technologies.
Membrane use responds to concerns about the tie of water and energy. Membranes remove contaminants other treatment technologies do not. They are more productive and occupy less space than the legacy operations they replace, such as those using sand. Therefore, membranes are a success of which the material sciences can be proud. According to Hanson, GE is continuing to invest in developing low-pressure membranes to save energy and withstand higher temperatures, extreme pH and rigorous handling.
A membrane, by definition, is a selective barrier allowing some things to pass through while stopping others. In its most basic form, it serves as a sieve, separating solids from the liquids forced through it.
Membrane markets can be divided into the well-understood mass-market applications of spiral-wound membranes, primarily for microfiltration, and complex, custom-engineering projects, sometimes involving hollow-fiber membranes. These hollow-fiber membranes, unlike the spiral wound, are fabricated by extrusion.
In wastewater treatment for an industrial process, the feed solution is the input water containing ions; organics; impurities, such as microorganisms; and suspended solids fed into the membrane element. The concentrate or brine is water exiting the membrane, which contains the rejected impurities. The levels of purification found in the purified water, or permeate, depend on the membrane type (see Figure 1).
Commercially available membranes efficiently filter particles down to the size of molecules or ions. Microfiltration, the most open of the membrane filtration processes, includes pore sizes ranging from 0.1 micron to 3.0 microns.
Membrane technology first came to maturity with the development of polymeric membranes, according to a January 2016 BCC Research report on global membrane markets. However, in process industries where one-size-fits-all filter systems or membranes are not possible, "growth will be modest over the forecast period."
On the other hand, many industrial product suppliers would love to attain the growth figures projected for membrane technology in the report:
- Global markets for microfiltration membranes, which reached almost $1.9 billion in 2015, should total $2.6 billion by 2020, reflecting a five-year compound annual growth rate (CAGR) of 6.7 percent.
- The biotech, bioprocessing and pharmaceutical segment is expected to reach nearly $1.5 billion by 2020 from $1 billion in 2015, increasing at a five-year CAGR of 7.7 percent.
- The drinking water application segment will grow from $334 million in 2015 to almost $474 million by 2020, reflecting a five-year CAGR of 7.2 percent.
The BCC report’s authors say barriers to continued rapid microfiltration membrane growth include the growing use of ultrafiltration, membranes’ long lives (up to 10 years) and industry maturity. While some spent membranes are refurbished, the analysts see the market as more interested in turnkey modularization or complete systems.
This analysis agrees with general process-industry trends toward greater reliance on turnkey; third-party services, given the scarcity of corporate-engineering services.
"If you’re speaking strictly of spiral-wound membranes, then you are speaking primarily of reverse osmosis (RO) and nanofiltration, and use in broadly two categories," Hanson said. "The largest group is primarily for salt removal, whether desalination or simply a boiler-feed application where clean water is needed to prevent scale-up. Almost any industrial plant is going to have a boiler, and the water used is going to be a concern. These are well-understood applications."
The other side of the market includes more challenging applications, according to Hanson. The membranes for microfiltration or nanofiltration also have organics, solids or other types of contaminants, not just salts. GE specifically plans to develop membranes that withstand higher temperatures, wider pH ranges and more aggressive cleaning, he said.
The BCC analysts focus on two market spaces, bio pharmaceutical and industrial, including food and beverage. Biopharmaceutical filtration offers generous returns to membrane suppliers, because high water purity is required for biopharmaceutical processes, resulting in frequent filter changes and the market has a global scope.
Industrial membrane filtration challenges include its reliance on government support for regulatory and environmental reasons and impact from the economic cycle. With membrane life expectancies prolonged, revenue from replacement filters falls short of that from new installations, and this affects equipment makers that rely on a steady stream of replacement-parts business as their most certain source of even cash flow.
However, increasing interest in industrial-site water reclamation offers a growth avenue, and semiconductor and electronics manufacture demand increasing water purity. In food and beverage, microfiltration is standard for certain dairy industry processes including recently developed milk-based liquid and popular high-protein, low-carbohydrate dairy beverages, but that does not hold true for the rest of the industry.
"Overall, the industry is fractionalized and material specific," said BCC Research analyst Lance Leverette. "The sheer number of competitors shows the maturity of the two most widely used materials: polyvinylidene fluoride (PVDF) and polyether sulfone (PES). For some applications, microfiltration membrane costs have dropped more than 80 percent since the 1990s."
The competitive landscape compels some membrane suppliers target high-revenue areas such as biopharmaceutical, while others increasingly turn to large-volume projects to drive growth.
Membranes commonly found in industrial settings include those for microfiltration, nanofiltration, ultrafiltration and RO.
Microfiltration and ultrafiltration use low-pressure membranes, either in a pressure or immersed system, for suspended solids removal following secondary clarification. Ultrafiltration membranes are effective for virus removal.Microfiltration is a low-pressure (10-to-100 psi) membrane process used to separate particulate from water down to sub-
In addition, microfiltration or ultrafiltration membranes are immersed in aeration tanks in a vacuum system, or they are implemented in external pressure-driven membrane units as a replacement for secondary clarifiers and tertiary polishing filters.
High-pressure membranes for nanofiltration or RO pressure systems treat and produce high-quality product water for indirect potable reuse and high-purity industrial process water.
"One challenge with membranes in wastewater treatment is the potential for fouling," said Khahil Z. Atasi, senior vice president with CDM Smith in a post on the company’s website. "Membrane fouling — caused by colloids, soluble organic compounds and microorganisms typically not removed well with conventional pretreatment methods — increases feed pressure and requires frequent membrane cleaning."
According to a December 2015 report from Transparency Market Research on membrane markets to the year 2020, the primary criteria for selecting a suitable membrane include membrane thickness, either with homogenous or heterogeneous structure, and pore size. In some cases, membranes can be either neutral or charged, and the flow of particles is either active or passive.
Particle transport can be facilitated by pressure, concentration, chemical or electrical gradients in the membrane process. Membrane filters do not need expensive or difficult-to-handle absorbents or solvents, and the equipment is simple and modular. Environmental concerns boost the membrane market because membranes reduce waste and enhance its general reuse.
Hanson sees GE continuing to invest in membrane technology, especially regarding low-energy and robust membranes. "The more salt that is present in the water, the more pressure required, and maintaining those pressures is very energy intensive," he said. "In a design environment focused on total life-cycle costs, research on salt removal at lower pressures continues." He added that using low-energy RO elements for drinking water and other applications, but not ultra pure water, is "taking off."
"As more uses are being found for membranes, membrane robustness improves because of the need for frequent cleanings, wider pH ranges and the ability to withstand higher continuous temperatures," Hanson said.
North America and Europe have the highest market demand for membrane filters because of their stringent environmental regulations, according to Transparency Market Research. Continuing research and development into high-performance membranes for industrial gas processing is also increasing demand in these regions. In the Asia Pacific, demand for membrane filters is high because of increasing water and wastewater treatment, with this rising demand expected to continue through the next few years.
- "Tubular membranes in industrial wastewater filtration systems & Technologies," Porex Filtration Division, porexfiltration.com/learning-center/technology/tmf-industrial-wasterwater/
- Atasi, K. Membrane Technology Advances Wastewater Treatment and Water Reuse, cdmsmith.com/en-US/Insights/Viewpoints/Membrane-Technology-Advances-Wastewater-Treatment-and-Water-Reuse.aspx
- BCC Research LLC, Wellesley, Massachusetts, bccresearch.com
- Transparency Market Research, transparencymarketresearch.com
Kevin Parker is the editor in chief of Processing magazine and group editor at large of Flow Control and Water Technology magazines. He may be reached at [email protected].