Recycling Water-Based Cleaners
Myth or Reality?

By Raymond J. Graffia, Jr.
February 2004

The Author is the President of the Arbortech Corporation in McHenry, Illinois, USA. His company offers a wide range of products, from ultrafiltration and R.O., and ideas to help clean up the environment and promote clean and safe methods to dispose of chemical and by product waste.

On fire with fervor, I barge in,
My placard reads, "More profit margin!"
Your cleaners aren´t spent
Just contaminants...
Recycle - stop dumpin´/rechargin´!

If it were only that easy... We´d all love to save the planet, keep it green, waste minimize and satisfy every other buzz phrase that is now or ever was a popular reflection of the sentiment toward reuse of vital resources. "Can´t be done, though (you might be thinking) - not here in this plant anyway. Our processes are unique; our cleanliness specs are so tight that there is no way we could recycle our water-based cleaning solutions." But it is an interesting premise nonetheless, isn´t it? What if there actually is a way to reclaim all that wastewater generated from your washing operations? "Shoot, if that was possible, we have one conveyor line with both pre-clean and clean stages; we´ve got a half-dozen stand alone turntable washers, plus our pre-paint five stage. And our plating tanks, soaks and electros - what if those could be extended too? What about floor washing? Hundreds of gallons in mop buckets all over the shop... more than that from our walk-behind and drive-around scrubbers. Think of the potential savings"

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, 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.

Advances in membrane materials and configurations continue to increase their energy efficiency, 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.

Pie-in-the-sky dream or reality? The premise here is the latter.

This article´s intent is to share recycling expertise so the reader can consider equipment to recover and reuse aqueous cleaners; so, suspend any disbelief for the next few minutes while we examine the wisdom in at least investigating the concept, beginning with an explanation of the heart of the technology itself - membranes.

Membranes have been around for years, in metal working plant applications from ultra-purification of incoming water to pre-treatment prior to sewer discharge of wastewater, the two most common uses within industry. Focusing on the end-of-pipe scheme, the membrane selected often has pores that, in comparison to others that may be available, would be categorized as relatively "tight" - in hopes of removing as much as can be practically achieved without severely curtailing the speed of processing. Materials of construction differ from vendor to vendor, but, in a majority of cases, consist of a polymer "skin" surface atop a fiberglass substrate. For limited pH range and ambient temperature projects, such as either of the above would typically be, these components serve well.

However, when dealing with highly alkaline cleaners or very low pH combination phosphatizer/degreasers, especially at the elevated temperatures often seen in washing operations, they simply do not hold up. Additionally, the benefits of "tightness" prior to sewer discharge will now actually be detrimental to reuse because some of the good stuff may be removed during the processing. Membranes intended for use in recycling are not so "tight," and are typically made to thrive under conditions where others might fail.

Floor Scrubber Concentrate

Arbortech´s Washer Washer (small scale) and WWPro (larger scale), for example, utilize titanium dioxide membranes with a 316L stainless steel substructure. Hence, this module and others so designed can tackle applications where pH is anywhere from 0-14, at temperatures to 200F - what it often takes to recycle water-based cleaners. The mechanism for removal and concentration of the "yuck" is cross-flow (not dead end as in traditional bag or cartridge filters), pressure-driven (generated by a circulation pump) and multiple pass, with the long-term effect being that oils and soils are retained on one side of the membrane, while the water plus materials in true solution with water (like the cleaning product) pass through to the other side. With an in-line system set-up, permeate (that which passes through the membrane) is normally returned directly to the wash bath while the reject is slowly concentrated in a small (compared to the wash bath) process tank for later removal and disposal. As a result, the wash bath stays perpetually near to freshly-made-up condition and the contamination concentrates in the recycling system´s process tank instead of the wash bath, therefore requiring no (or at least greatly reduced) dump/recharge - just continual reuse.

In one unusually successful case, a company that formerly dumped and recharged its 5,000+ gallon bath quarterly before implementing a recycling system, only did so once in the next seven years... when they moved the operation out of one building and into another. While this performance is quite extraordinary, prolonging of bath life from four to six times is very common. Beyond extended bath life, what other direct or indirect contributions to the bottom line might be expected from installation of a good recycling system?

Floor Scrubber Solution Alkaline Cleaner Concentrate
Floor Scrubber Solution Concentrate on Left Permeate on Right Alkaline Cleaner Concentrate on Left Permeate on Right
Iron Phosphate Concentrate Floor Scrubber Concentrate
Iron Phosphate Concentrate on Left Permeate on Right Floor Scrubber Concentrate on Right Permeate on Left

There are nine fundamental reasons to at least consider investigation:

Some final words to the wise...

Pick your potential recycling partner carefully. Writing about the benefits of reclamation and "sales pitching" a product to accomplish this objective are both relatively easy. The willingness and ability to prove the application at your specific site, with your incoming water quality, your operating personnel, your chemicals and your contaminants are much better standards against which to measure. Vendors with capabilities to run bench scale demonstrations followed by in-the-field pilot scale testing... all done prior to your issuance of a purchase order to buy a system, may also be the ones best suited to stand up and be counted when Murphy visits you long after the final payment check has cleared.

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Copyright © 2004, ECO Services International