Arbortech - Aqueous Cleaner Recycling Equipment Manufacturer

Excerpts taken from:

Opening the
'Black Box':
Regulations and Recycling Drive Use of Membrane Technologies

by John Krukowski, Chief Editor

A popular magazine cartoon of more than a decade ago depicted a scientist at work at a blackboard. Either side of the board was filled with dense formulae representing two phases of a complex chemical or mechanical process; in the middle, the professor simply had scribbled, "And then a miracle occurs." A colleague standing nearby points to this and dryly comments, "Maybe you should be more specific."

For years, many environmental professionals tended to take a similar view of membrane separation technologies as mysterious, "black box" processes that needed to be better understood before would-be users would commit to installing membrane units in their facilities. Today, however, users' comfort level with membranes is growing as regulatory and market pressures are forcing them to look for new technologies to capture solids, remove impurities and reuse water.

The MP&M Rule

Tens of thousands of facilities soon will be required to reduce metals content in their effluent by half or better. The rule is expected to create new interest in closed-loop recycling, and could prompt many plants to adopt membrane technologies.
Indeed, when U.S. EPA proposed the Metal Products and Machinery (MP&M) rule earlier this year, it gave tacit endorsement of microfiltration as a technology option for wastewater containing flocculated metal hydroxide particles:
"Well-operated chemical precipitation and microfiltration systems sampled by EPA at MP&M facilities achieved an average removal of 99.6 percent for targeted metals. Well-operated chemical precipitation and gravity clarification systems sampled by EPA at MP&M facilities achieved an average removal of 96.7 percent for targeted metals." (www.epa.gov/ost/guide/mpm/rule.html)
The MP&M rule affects many industries that produce wastewaters containing oils, organics, cyanide, hexavalent chromium, complexed metals and dissolved metals. EPA estimates compliance will cost nearly $2 billion annually, and eliminate the annual discharge of 170 million pounds of pollutants.
For more information, read "Metal Product Manufacturers Next in Line for EPA's Effluent Guidelines," March 1999, Pollution Engineering.

"Around 10 years ago, many people wouldn't have even heard of membranes," says Dr. Kishore Rajagopalan, a group leader in the Waste Management and Research Center (WMRC), Champaign, Ill. Most industrial use of membranes at the time, according to Rajagopalan, was limited to the biotechnology or dairy and food products industries. For public utilities, desalination was the usual application.

Today, a much greater variety of manufacturers and municipal treatment plants are finding uses for membrane systems, as Rajagopalan and others can attest. The WMRC's Pilot Technology Laboratory, for instance, is busy evaluating and demonstrating the efficacy of membranes for a variety of industries, many of them quite far removed from biotech. In one recent case, WMRC helped a Chicago-area manufacturer dramatically lower the suspended solids level in its discharge, conserve its use of chemicals and cut operating costs through the use of an ultrafiltration (UF) system (see "Pilot Testing" below.)

In terms of sales, membranes represent a growing portion of the total industrial and municipal market for wastewater treatment equipment. "Membrane technology has seen steady growth in the last 10 years, in the 5 percent to 10 percent annual range," says Grant Ferrier, industry analyst and president of Environmental Business International, San Diego. Ferrier predicts "healthy growth of 7 percent to 9 percent annually through 2005 as membranes find new applications and replace other filtration and separation technologies.

"Growth goes up as square-foot costs of membranes continue to come down and as market acceptance [grows]. This is occurring especially in water reuse, industrial ultrapure [applications] and even drinking water systems."

A changing view of water

"The industrial end-user is more educated, and [today's] facilities managers are performing integrated water management," notes Tom Wingfield, (who works in the membrane filtration industry). That means engineers are more likely to view water from the standpoint of an entire facility's operations, rather than narrowly and in the context of a single application.

Wingfield explains this is because industry increasingly views water not as a "commodity, [but as] a resource." Closed-loop water recycling is a common goal in fact, nearly half of Pollution Engineering readers report their facilities are actively trying to reclaim water for reuse, according to a recent survey.

Because of these factors, Wingfield says process and environmental engineers are more conscious of how a chemical say, a flocculent added at one point in the process can impact other steps. "Users will say to us, 'don't complicate my water chemistry and, sometimes, my biology.' They are looking for mechanical separation techniques rather than adding more chemicals to the water mass."

The drive for water reuse has changed attitudes about membranes and other technologies that Wingfield says formerly might have been given "short shrift" by potential users. That, along with concerns about the risks of using treatment chemicals, which he also notes are in many cases the foremost contributor to operational costs. (A recent survey of water utilities by Denver-based consultant Richard P. Arber Associates found that reduced chemical consumption was one of the biggest drivers behind their adoption of membrane technologies.)

Different membrane types are filling niches in specific applications, often as replacements for older technologies. Reverse osmosis (RO), for example, is well known as a replacement for evaporation and distillation in making potable water. And Wingfield says microfiltration (MF) is replacing sand filters in some industrial and municipal wastewater applications, where it is paired with RO for water reclamation. UF systems are used for volume reduction and to segregate streams in industrial applications with colloidal and high molecular weight constituents.

UF systems are generating a lot of interest in municipal applications, too, notes Karen Rasmussen, an analyst with Frost & Sullivan, San Jose, Calif. "As membrane prices have gone down and the technology has improved, you're [also] seeing less fouling and more reliability," she says.

Some common applications pair membranes with other technologies, Wingfield notes. In the microelectronics industry, for example, an RO/ion exchange treatment train is not unusual.

Membrane Types: The Basics

Often referred to as "filtration," membrane systems nonetheless operate differently from conventional filtration, such as sand filters. Unlike those processes, membranes don't rely on particles becoming entrapped within the filter matrix. Instead, the filtration occurs at the surface of the filter, where "permeate" is able to penetrate the membrane's pores, while "concentrate" too large to make it through the pores is captured at the surface. In a common membrane configuration (cross-flow filtration) the feed and concentrate flow is parallel to the membrane surface, allowing contaminants to be carried off.
The four most-common membrane types are classified by their pore sizes.
Microfiltration (MF) has pores from 0.1 micron to 1 micron and can be used to remove bacteria and suspended solids. MF elements typically are made of polymeric material such as Teflon or polyacrylonitrile, although ceramic or metallic materials also are used.
The next smaller pore size in membranes is ultrafiltration (UF), generally 0.003 micron to 0.1 micron. UF removes most non-ionic material, including colloids, viruses and certain proteins.
With nanofiltration (NF), pore sizes are much smaller (0.001 micron to 0.003 micron) and greater pressure is required to pass liquids through the membranes. NF rejects concentrate in two ways: Non-charged soluble organics physically are too large to pass through, while charged soluble salts smaller than the pores are rejected because water is more soluble in the membrane than the salts. These membranes typically are made of a polymeric base and thin film composite.
Reverse osmosis (RO) systems have membrane pores of approximately 0.0005 micron. RO units perhaps are best known for desalination, but they also have industrial applications in, for example, concentrating sugars in food processing or removing toxic metals from electroplating streams.
RO systems rely on pressure to cause water to flow through a membrane from a concentrated solution to a dilute solution. Their energy efficiency, thanks to improved membrane materials, has steadily improved. Consultant Richard P. Arber recalls when typical UF systems required pressures of 300 psi to 400 psi; today, he says, pressure requirements of 100 psi to 200 psi are common.

In the power industry, MF followed by RO is used to reuse water for cooling towers.

But while the cost of water remains a major concern of utilities and industry, regulations also are driving membrane use. New Metal Products and Machinery (MP&M) effluent limitations and pretreatment standards, for example, mean that traditional sand filters "aren't going to cut it" in many applications. Because of tighter guidelines like MP&M, he says, "Most of our customers see they have membranes in their future." (See "The MP&M Rule" sidebar.)

Don't skimp on pilot testing

Consultants and vendors, "have done enough work [with membranes] that we're comfortable with the technology." But clients are not as fluent with membrane systems, so (equipment vendors) and others stress the importance of pilot testing.

"Often people hear horror stories about a guy who buys a $100,000 system and it fails in the first six hours," says WMRC's Rajagopalan. Perhaps left unsaid in those environmental urban legends is the fact that the user did not spend enough time testing the unit to evaluate fouling characteristics, and pretreatment and cleaning requirements. Or, whether a membrane system even made sense for the application.

"Make sure your application is a good fit," cautions consultant Richard Arber. "Not every application fits membranes." Petroleum products, he notes, often are not a good match. (That might be changing, however see the "Emerging Membrane Technologies" sidebar.)

At a minimum, users should not view membrane systems as a one-size-fits-all solution. "There really is no drop-in solution," Rajagopalan says, "because there are so many different chemistries out there."

WMRC recently helped Werner Co., a manufacturer of ladders, select the best closed-loop recycling process for its facility in Franklin Park, Ill. The plant generated about 1500 gallons per day of cleaning/deburring solution. The stream constituent of greatest concern was fats/oils/grease (FOG), which sometimes exceeded the limit of 250 mg/l. In addition, the plant risked a surcharge for its total suspended solids (TSS) content.

Several potential solutions were evaluated, including the use of a hydrocyclone, coarse filtration and chemical treatment. These were ruled out for reasons of performance or cost.

For one month, engineers also pilot tested a UF system manufactured by Arbortech Corp., McHenry, Ill., equipped with a series of four, eight-foot-long tubular membranes. Through experimentation, WMRC was able to improve flux enough to allow a substantial reduction in membrane area, reducing the eventual cost of the full-scale UF system by more than half.

Using UF for its closed-loop recycling, Rajagopalan reports, Werner has been able to:

Reduce FOG levels to less than 30 mg/l.
"Drastically" reduce TSS.
Reduce the facility's use of deburring chemicals by more than 50 percent.
Eliminate discharge of deburring solution to the local publicly owned treatment works.

Werner typifies today's company that is pursuing closed-loop recycling both for economic and regulatory reasons. And, through careful evaluation of its options, it has successfully adopted a membrane technology solution.

Although not a part of the above re-printed article, Arbortech's Ray Graffia Jr. reports that Werner's continuing success can be , at least in part, attributed to a change in the cleaning/deburring chemistry. Werner now uses Arbortech Corporation's own membrane cleaner,"TUF", to clean and debur its parts. The UF system is thriving, processing speed is consistently high, and the parts are reportedly, "cleaner than ever," as related to Graffia during a visit to the plant mid-July 2001.

Emerging Membrane Technologies

Membranes themselves are not a new technology. But advances in membrane materials and configurations continue to increase the reliability and applicability of these processes.

Significant breakthroughs have included composite polyamide membranes capable of removing 99.5 percent of dissolved ions at feed pressures of less than 200 psi, and oxidant- and chemical-resistant membranes for MF and UF applications. A sampling of other noteworthy developments includes:

Research at Rensselaer

In the academic world, Prof. William N. Gill of Rensselaer Polytechnic Institute, Troy, N.Y., has been notably active in research to improve the performance of membranes. The Russell Sage Distinguished Research Professor in Chemical Engineering has co-authored numerous papers on the use of RO and other membranes in the microelectronics and metal finishing industries.

"There has not been sufficient attention given to the economic benefits of membrane separations," Gill says. Several papers he has coauthored shed light on how membrane performance might be improved to increase economic and environmental payback.

For example, at a meeting of the American Council for an Energy-Efficient Economy (ACEEE), Gill and fellow Rensselaer researchers presented the results of a study of an RO membrane that successfully processed extreme-pH (13.5) copper cyanide rinse water for up to four months with no decrease in flux or rejection observed. That was the sort of harsh environment an RO unit would encounter in processing copper cyanide rinse waters; previously some commercially available membranes were purported to survive a pH of "only" 12.

A scanning electron microscope study showed no breakdown of the membrane surface's "ridge and valley" polymeric structure. Also, the Rensselaer team found pretreatment with an ethanol solution improved the membrane's flux fivefold. (Goel, M., et al. "Hazardous Source and Waste Reduction in Metals Finishing Industry by Hybrid Membrane Separation Process," ACEEE 1995 Summer Study on Energy Efficiency in Industry, pp. 617-628. Results of a study that exposed RO membranes to high pH solutions for up to six months were published in Goel, M., et al. "Stability and Transport Characteristics of RO Membranes Using Cyanide Rinse Waters," Journal of Membrane Science 141, 1998, pp. 245-254.)

Of interest to readers in the semiconductor industry, Gill and his peers have documented the use of an RO system in reprocessing hydrofluoric (HF) acid etch waste. The "reprocessor," according to the Rensselaer scientists, "has the potential to be a part of both an environmental pollution reduction strategy, and a source of new ultrapure etching solutions." (Gill, W., et al. "Novel Membrane-Based Systems for Reprocessing HF Acid Etching Wastes," Advances in Environmental Research, 2 (3) 1998, pp. 333-350.)