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The Benefits of a Membrane Recycling System

Membranes have been around and in successful use for decades. However, over the past 10 to 15 years membranes have served a third function—recycling water-based cleaners.

Ray Graffia, Jr.

What makes us buy one particular cereal when there are 46 others on the shelf? Or watch a program at 7 p.m. when there are, via cable and satellite anyway, 600 alternative options? A quick answer to the two aforementioned queries would probably be, “because that’s what I like,” however, the cereal commercial must have been intriguing or maybe you decided to try it on a reference from a family member or trusted colleague. Some unique characteristic entices us to sample or explore this or that, following which we find it to be pleasing or worthwhile. This certainly does not demean the other breakfast foods or television series, which also may turn out to be  favorites when/if we are exposed to them, but it does serve to point out the importance of product differentiation. 

There is no denying the existence of other factors beyond simple comparison and/or exposure. You might truly crave a new Mustang, Viper or “Vette,” but if all you can afford is a used Yugo, desire becomes moot. But, where pricing is similar or the differences justifiable, whether in reality or simply in the eyes of the beholder, being different could be a key to success. Therein lies not only the challenge to the sales and marketing departments of purveyors of goods but also to the consumers whose eyes and ears are besieged with ads and whose dollars are being pursued from so many angles. How can companies gain enough attention from the consumer—small business owner, maintenance supervisor or EHS engineer—to make their products known and do justice to the options that are available when taking on the task of assessing choices on any given project?

Membrane Technologies

We hear comments like these all the time…  “Parts are just not getting clean enough. Our post-wash coatings are not passing salt spray specs, wash operation costs are out of control, hauling expenses keep spiraling higher and higher and we need to do better on our waste minimization plans.” Each of these might be addressed by discerning a new cleaning technique or device, comparing several cleaning chemistries or looking at the plethora of in-house wastewater treatment technologies. At least those are the traditional things to consider. But what about thinking outside the box and shifting the paradigm? Why not approach the problem in a different manner? Why not consider recycling your wash solutions instead of dumping and recharging them? Why not look at membrane technologies to reclaim and reuse your cleaners and look at what’s out there and what makes each different?

Which is the recycled alkaline cleaner? It's as clear as night from day.

Membranes have been around and in successful use for decades. The two principal metal-working plant applications are ultra-purification of incoming water (a common use where parts’ cleaning is concerned) and pre-treatment of wastewater prior to sewer discharge. Over the past 10 to 15 years, however, membranes have served a third function—recycling water-based cleaners. Reverse osmosis (commonly referred to as RO) membranes, can be used to ultra-purify your incoming water. The membrane selected often has pores that, in comparison to others, like RO modules,  would be categorized as relatively “tight” - in hopes of removing as much as can be practically achieved without severely curtailing the speed of processing.

 Membrane materials of construction differ from vendor to vendor on such systems, but, in a majority of cases, consist of a polymer “skin” surface atop a fiberglass substrate. For limited pH range and ambient temperature projects, these components serve well when focusing less on recycling and more on wastewater treatment. 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.

 The benefits of “tightness”—desirable in making ultra-pure water or for projects involving sewer discharge—will now actually be detrimental to reuse because some of the good stuff may be removed during processing. Membranes intended for use in recycling are best if they are not so “tight,” and made to thrive under conditions where others might fail. For example, systems that use titanium dioxide membranes with a 316L stainless steel substructure  can tackle applications where pH is anywhere from zero to14, at temperatures to 200 degrees F. Therefore, when recycling aqueous cleaners in-line directly at the wash bath, such widely diverse conditions may be demanded of the equipment and must be compensated for in membrane selection.

 To further differentiate such systems, the flow pattern  for removal and concentration of the “yuck” is across the module as opposed to dead end filtration as in traditional bag or cartridge filters (Think of the contaminants as shooting across the top of your desk versus dropping from the ceiling and piling up atop your desk…), 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 process tank (when compared to the volume in your wash bath 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) dumps and recharges—just continuing reuse.

Installing a Membrane Recycling System

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 bath life four to six times or more 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 membrane recycling system?

 There are nine fundamental reasons to at least consider investigation:

1. Improves parts’ cleanliness—If the condition of the wash bath is consistently high quality, the washing process will be enhanced and parts cleaned will always be at maximum purity. You know how well your bath cleans just after a dump/recharge; why not just keep it that way, essentially permanently?
2. Improves rinsing—Typical washing operations result in transfer by carry-over of a small portion of the wash bath to the subsequent rinse stage. Where this carry-over is highly contaminated, the negative consequences and wasted water at the rinse stage can be dramatic. (The solution to pollution need not be dilution!) After installing adequate recycling, including counter-flowing measures, rinse stages that formerly overflowed at high rates have been reduced to lower rates, and, in some cases, even turned into standing rinses.
3. Improves subsequent steps—How difficult is it to paint, powder coat or plate a part that has not been properly cleaned?  By maintaining wash bath cleanliness, those issues and the accompanying rejects attributable to poor cleaning often disappear.
4. Increases production—Is your wash process a production bottleneck?  If so, forget about ever-shortening cycles of dump and recharge, because recycling can keep high quality cleaning virtually perpetually available. To reiterate, just think about your reject rate on parts … how much might it be reduced if they came out consistently clean?
5. Reduces labor costs—Do you dump and recharge on straight time or overtime?  Many companies do such work after hours or on weekends, making the labor costs even greater.  And how about the dollars spent addressing all the paperwork required for proper handling and disposal of the wastewater? 
6. Saves power—Whether you heat by gas or electricity, as your wash bath deteriorates one common performance booster is to turn up the heat and that can be expensive. The potential to maintain or even lower the operating temperature in a wash bath is an increasingly important reason to consider membrane recycling.
7. Saves hauling costs—When was the last time that your cost per gallon to haul this “stuff” away was reduced?  How is such a price reduction even possible?  Since the hauler’s first objective is usually to dewater the product hauled, if you remove most of the water and present them with a far stronger concentrated solution, this saves them costs and saves you money.
8. Saves water—In portions of the world where good quality water is scarce and a precious commodity, keeping a 5,000 gallon bath in use instead of recharging it three to four times per year would be substantial conservation. Further, consider the reduction in water usage if recycling can enable a rinse overflow to be reduced, for example, from 3 gpm to 2 or 1 gpm, or even eliminated.

Typical Membrane Materials

Now that you are convinced to check out recycling with membranes, what are your options? Let’s review the three most typical membrane materials of construction and kick around the compatibilities for each. This trio includes: polymerics, ceramics and sintered metals. How do they differ?

Polymer membranes typically can only function with decent longevity under circumstances where both pH and temperature are limited. A pH range of 3.5 to 10.5 might be expected, with the ability to sustain exposure to an operating bath temperature of perhaps 130-140F maximum. Eventually, even where material incompatibility does not lead to failure, compression of the membrane substrate leads to decreased productivity on the permeate (treated/recycled water) side; over time these membranes need to be replaced.

Ceramics and sintered metals, on the other hand, can often tolerate almost any extremes that one might see in a washing operation. Both are typically suitable for any pH—across the full 0 to 14 range and temperatures as high as anyone uses to clean. However, temperature variation to a point where the far more fragile ceramics might crack could lead to premature failure of those. Additionally, where the membrane recycling system includes the option for offsite restoration of membrane performance, the ability to ship ceramic membrane modules back and forth would not be a viable option due to the rough handling common when using commercial shipping firms, like UPS, Fed-Ex, DHL, etc. A fractured ceramic membrane must be replaced and that costs a lot of money; hence, the most bullet-proof of these three membrane materials of construction is sintered metal. How rugged are they? Where factory membrane restoration is an option, seventy-five percent or more of those end users utilize this service to keep their membranes in tip-top shape.

Some Final Words to the Wise

Presuming that you are driven to at least explore recycling, look for things that differentiate one vendor from another; pick your potential partner carefully. Writing about the benefits of reclamation and “sales pitching” a product that can accomplish this objective are both relatively easy. Remember the old phrase, “Words are cheap!” The willingness and wherewithal to prove the application at your site, with your incoming water quality, your operating personnel, your cleaning chemicals and your contaminants are much better standards against which to measure viability of one system manufacturer versus another. Vendors with capabilities to run bench scale demonstrations followed by in-the-field pilot scale testing, may be the ones best suited to stand up and be counted if “Murphy” ever visits you after the final payment check has cleared. What can go wrong probably will, so do your homework, be thorough in your evaluations and testing, and keep an open mind.