New materials, designs and digitalization provide cost-effective, long-term membrane-system performance
Chemical processors prioritize uptime and high performance in membrane and filtration systems, so innovative technologies are being developed to minimize downtime and provide more cost-effective long-term performance in challenging chemical processes and wastewater recovery and recycling applications.
“Processors demand stable and reliable performance because unplanned downtime translates directly into significant lost profit opportunity,” says Jay Horowitz, applications engineer with W.L. Gore & Associates (Elkton, Md.; www.gore.com).
Several common issues contribute to costly downtime and poor performance in membrane and filtration systems. Dominik Schreier, director of global engineering WMS with Mann+Hummel Water and Membrane Solutions for cleaner water (Ludwigsburg, Germany; www.mann-hummel.com), explains the hurdles: “Chemical processors face three major challenges when it comes to membranes and filters. The first is fouling, especially biofouling, and the second is scaling. If you can reduce both of those, you can directly improve efficiency and, at the same time, increase permeate productivity.
“The third challenge is chemical and thermal stability,” Schreier continues. “That’s not only important in the filtration applications themselves, but they’re also critical during cleaning processes with harsh agents at wide pH ranges and at higher temperatures.”
Fortunately, new technologies are available to address common operational challenges and improve performance.
Enhancing performance
Fouling is one of the biggest causes of poor performance and high operating expenses, so providers focus heavily on developing technologies aimed at reducing fouling, which in turn boosts recovery rates, uptime and efficiency and lowers costs.
For example, hollow-fiber ultrafiltration (UF) membranes are often used in reverse osmosis (RO) pretreatment, especially in water reuse projects, but RO biofouling can lead to significant downtime for cleaning and shortened RO membrane life. However, new UF membranes, called Fine UF, developed by Toray Industries (Tokyo, Japan; www.toray.com) have smaller, finer pore sizes (in the single-digit nanometers) than conventional UF membranes, so they are capable of rejecting the dissolved organics that cause biofouling of RO membranes. “As a result, RO membranes will foul at a slower rate, which will reduce downtime for cleaning, extend RO membrane life, minimize the cost of chemical cleaners and reduce power consumption,” says Sean Carter, sales director with Toray Membrane USA.
Mann+Hummel’s Schreier says: “Fouling is caused not only by the membrane properties alone, but also by the overall element construction. Spiral-wound elements, the most commonly used, have specific feed spacer designs to reduce fouling propensity and optimize pressure loss.
“Low-fouling constructions help in two ways,” he continues. “First, they increase the recovery rate of valuable products. Second, they reduce the downtime needed for cleaning, which leads to a higher product yield, lower investment cost and lower energy consumption/input for filtration for overall lower operating expenses.”
Mann+Hummel provides TurboClean sanitary membrane elements (Figure 1), which feature a rugged polypropylene shell that results in a stronger, more rigid and durable element that is better suited to challenging applications, such as the processing of dairy products, sweeteners, beer and wine, pharmaceutical products and proteins.
FIGURE 1. TurboClean sanitary membrane elements from Mann+Hummel feature a rugged polypropylene shell that results in a stronger, more rigid and durable element that is better suited to challenging applications
TurboClean elements are available with all membrane types (RO, nanofiltration (NF), UF, and microfiltration (MF)), and are manufactured to a precise diameter that reduces bypass flow by 60% or more when compared to conventional full-fit, net-wrapped or caged membrane elements.
The reduced bypass flow provides up to 35% water savings and 22% energy savings, while also maximizing cross-flow velocity at the membrane surface for enhanced product throughput and better overall product yields. The lower bypass flow also allows more of the cleaning solution to flow inside of the membrane element and across the membrane surface. In addition to better performance during operation, higher crossflow velocity results in more effective cleaning and lower microbial levels.
Performance degradation is another common — and costly — issue related to fouling in industries operating at pH 0 through 14, says Gore’s Horowitz. “Performance degradation typically manifests in one of two ways: either as increased breakthrough of unwanted materials into the filtrate or as a pressure drop that fails to recover after cleaning cycles.
“Cleaning frequency and duration govern a plant’s overall capacity utilization,” says Horowitz. “In some facilities, you see ten or more sequential filtration steps, with one or more stages requiring chemical additives that need to be removed by a subsequent stage. That kind of process complexity adds capital and operational costs.”
He says that there is ongoing development of new polymers for extreme chemical environments, including Gore’s products, which use polymers that are chemically resistant across the pH spectrum. “Gore Membrane Filter Sock and Tube Assemblies use expanded polytetrafluoroethylene (ePTFE), one of the most chemically stable polymer materials. Its resistance to chemical attack enables our products to achieve operational lifetimes that most filtration technologies cannot approach (Figure 2).
FIGURE 2. Gore Membrane Filter Sock and Tube Assemblies use expanded ePTFE which resists chemical attack to achiever longer operational lifetime
“That said, many advances are not purely about materials, they are about process design,” notes Horowitz, who points to Gore’s Tubular Back-Pulse Filters. “Rather than driving particles into the membrane depth, we build them up as a filtration cake on the membrane surface and then remove that cake through a back-pulse cleaning cycle,” he says. “When operated properly, this approach sustains a durable and long-life membrane filter. Properly maintained installations have lasted more than 10 years in continuous production.”
Because the particles are not being embedded into the membrane, the back-pulse (the primary cleaning mechanism) briefly reverses liquid flow to dislodge the surface cake. “The membrane itself is not being exhausted. However, even surface-filtration systems must contend with scaling or fouling from unplanned impurities or process upsets. If desired, plants can further restore differential pressure through a highly effective acid wash, conducted infrequently or periodically,” says Horowitz. “The good news is that our ePTFE-based Membrane Sock and Tube Assemblies are fully resistant to pH levels of 0 through 14, making them completely compatible with strong acidic or strong basic cleanings.”
The benefits of this effective low-fouling design are tangible: longer filtration cycles, reduced cleaning frequency and shorter cleaning duration, all of which translate into higher plant utilization and lower operating costs, explains Horowitz.
Another approach to combat fouling in challenging applications, including very difficult wastewater recovery and recycling processes that have struggled with conventional membrane performance, comes from New Logic Research (Minden, Nev.; www.vsep.com). The company’s Vibratory Shear Enhanced Processing System, or VSEP, is a unique membrane system that resonates to vibrate the membrane, creating very high shear at the membrane surface to reduce fouling, scaling and plugging (Figure 3).
FIGURE 3. The Vibratory Shear Enhanced Processing System, or VSEP, from New Logic Research is a unique membrane system that resonates to vibrate the membrane, creating very high shear at the membrane surface to reduce fouling, scaling and plugging
The VSEP system uses torsional oscillation to create very high shear at the membrane surface, which disrupts concentration polarization and prevents scaling. While other membranes are limited by solubility, VSEP can work like a membrane-crystallizer, precipitating solids during the filtration process.
“The vibration has the effect of keeping the membrane from fouling, scaling or plugging,” says Greg Johnson, New Logic Research CEO. “Our membrane is used where the selectivity of a membrane is desired but conventional spiral membranes cannot be used due to fouling and scaling potential, including very difficult effluent streams.
“The advantage of VSEP is the simplicity,” notes Johnson. “We can take raw wastewater and, without pretreatment, make very clean water. There may be less expensive solutions, but they often involve a complicated system with many different pieces of equipment working in series. Instead, our process simply agitates the membrane by moving it back and forth, creating very high shear, which makes it difficult for particles to attach to the membrane, so it suppresses fouling and scaling of the membrane to reduce cleaning frequency.”
Wastewater recovery
“As global water shortages become more severe, manufacturers are increasingly turning to recycled wastewater and seawater as alternative sources for ultrapure water. Industries that consume vast amounts of ultrapure water require advanced filtration technologies capable of removing a variety of impurities, including salts, silica, boron, urea and alcohols,” says Toray’s Carter.
“Urea, in particular, is a major challenge due to its small molecular size and neutral charge, which makes it difficult to remove efficiently,” he says. “Our new technologies have been designed to address this challenge.”
Toray Industries TBW-HR and TBW-XHR ultra-low pressure RO membrane elements were designed to improve the rejection of silica, boron and other neutral molecules from water by controlling RO membrane micropore sizes and membrane structures (Figure 4).
FIGURE 4. Toray Industries TBW-HR and TBW-XHR ultra-low pressure RO membrane elements were designed to improve the rejection of silica, boron and other neutral molecules from water by controlling RO membrane micropore sizes and membrane structures
Impurity rejection with TBW-HR and TBW-XHR elements exceeds that of existing ultralow-pressure RO membrane elements. A key prospective benefit is purification of higher-quality and higher-purity water, which is essential, as demand for extremely high water purity has risen in industries such as electronics and semiconductor production.
For the TBW-HR series, Toray developed an RO membrane element with double the neutral molecular component rejection capacity of the company’s conventional offerings while maintaining low operating pressures. High solute rejection is achieved by precisely controlling RO membrane micropore sizes and enhancing the membrane polyamide structure.
The TBW-XHR series membranes use a new manufacturing technology that enhances the removal of urea, boron, alcohols and other substances while maintaining high water permeability at low pressure. Internal testing has demonstrated that the urea removal efficiency of the TBW-XHR membranes is nearly 90% at system conditions, a previously unheard-of removal rate by brackish-water RO membranes.
“This is particularly valuable for producing ultrapure water from recycled wastewater, which often contains urea concentrations much higher than those found in tap water and with the increasing demand for sustainable water sources, this innovation provides a solution that not only improves water quality, but supports the global transition to more circular and environmentally friendly water treatment practices,” says Carter.
Also recognizing the growing need to support tough wastewater recovery and recycling applications, Horowitz says Gore has entered into a strategic partnership with Membrion (Seattle, Wash.; www.membrion.com), a company developing ceramic electrochemical membranes designed for highly acidic, metal-laden industrial wastewater streams, such as mining operations, semiconductor fabs and battery recycling.
Membrion’s Electro-Ceramic Desalination (ECD) technology continuously separates dissolved metals and salts into a concentrated side stream so treatment performance remains stable.
Using ceramic membranes and an applied electrical field, Membrion’s technology actively transports dissolved ions out of wastewater as it flows through the system. Instead of relying on pressure, chemical precipitation or ion exchange, the electrical field drives targeted ions across the membrane into a small, concentrated side stream.
Because the membranes are ceramic, rather than polymeric, they tolerate harsh industrial conditions, including low pH conditions, foulants, oxidizers, solvents and complex wastewater chemistry. The result is stable treatment performance in streams where conventional filtration systems struggle or require significant pre-treatment.
“Membrion’s ceramic electrochemical membrane technology represents the cutting edge of what is possible in the most demanding industrial wastewater environment,” says Horowitz.
As advances and innovation continue, processors can expect to achieve higher performance with less downtime and lower operating costs to support even the most challenging wastewater recovery and process applications.
Digital Platforms Enhance System Performance
By providing continuous intelligent recommendations and monitoring, digital platforms can help enhance system performance of water treatment applications.
For example, Mann+Hummel offers a digital platform, STREAMETRIC, that monitors and logs key operational and maintenance data of water and wastewater systems. “It alerts if conditions are becoming critical for membrane systems and allows adjusting process parameters to maintain optimal conditions and cleaning intervals,” says Schreier. “Our customers and service teams use the platform to ensure a reliable, observable and robust membrane system operation, day to day, maximizing uptime of membrane systems.”
And, Kurita America (Minneapolis, Minn.; www.kuritaamerica.com) offers Kurita Connect360 (currently available in Europe and soon to be available in the U.S.), which serves as a global digital platform designed to centralize monitoring, analytics and reporting across water treatment applications like cooling, boiler, membrane and wastewater systems. The platform integrates smart monitoring, reporting and analytics into a single interface. It provides sustainability dashboards that quantify water and CO2 metrics, serving as a digital backbone that standardizes KPIs and turns field data into actionable insight for operational excellence and sustainability performance.
Another part of Kurita’s digital toolbox, the S. Sensing RO-AS (Reverse Osmosis Anti Scalant) device, defines the minimum effective dose and maximum achievable recovery, along with key parameters to monitor to achieve stable RO or NF system operation.
When combined with Avista AdvisorCI modeling and Chromatic Elemental Imaging, Kurita’s service provides confirmation of membrane performance to help verify the correct anti-scalant doses under real operating conditions, identify the minimum effective dose to reduce chemical costs, validate maximum recovery to enhance water production and validate performance in real time through an analytical lens. The technologies can also help provide confidence in product selection and system design.
“Using the AdvisorCI software modeling program and the RO-AS sensing device, we can gain accuracy in our modeling to provide better predictive water analysis with more realistic limits on very high recovery projects,” says Ken Robinson, director of applied technology with Kurita.
“As industry continues to push recovery limits further, the more risk you have and the more difficult it is to understand the realistic expectations of a system,” says Robinson. “So, we’ve developed this analytical program as part of our automation monitoring and digital program to provide a more realistic snapshot of the limits of concentrating that water and reducing waste.
“Having better analytics brings a better process outcome, which reduces the risk of poor performance in water treatment projects. This is critical because it’s one thing to assume a technology will provide a certain result and another to have the confidence that it will produce a good result,” says Robinson. ❏
– Joy LePree