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A metal hardware contract manufacturer solves the difficult problem of managing its effluent with a turnkey process that separates solids and recycles water.
By Don Talend
Even without the costs involved in managing pollutant production byproducts, it’s difficult enough for a US firm to succeed in manufacturing, given global competitive pressures, lower labor costs in many other countries, and the volatile prices of some commodities. Add to the equation the costs and labor involved in environmental stewardship, and competing in the global economy becomes even more difficult. For some US manufacturers, byproducts that result from wet production processes may be harmful to groundwater if not treated properly onsite or handled by a vendor—at a considerable operational cost.
One such company that is trying to compete in the hypercompetitive global economy with these inherent water conservation challenges is Line Tool & Stamping Co. of Arlington Heights, IL. The 80-employee company is a contract manufacturer of various industrial products for industries such as automotive aftermarket, fractional-horsepower motors, and material handling for customers such as General Electric and Honeywell. Its tools, dies, and punch presses produce components that not only need to be smoothed down but also require removal of oil residue, explains Al Panico, president and owner of Line Tool & Stamping Co. He explains that customers require parts with no sharp edges, necessitating a mass vibratory finishing operation.
At Line Tool & Stamping Co., parts are transported from a punch press to one of two circular mass vibratory finishing machines partially filled with finishing media, a continuous feed of water and a rust inhibitor (referred to as “soap”) for the parts. Typically, Panico notes, the media are angular and made of ceramic clay, which smoothes out rough edges without deforming parts. A motor with weights on each end produces vibration in the machine’s tub, generating friction among the media and the parts. When the finishing cycle is complete, a vertical “dam” is raised and parts are diverted to a drying machine that uses media made from corncobs.
Because this finishing process is a wet process, it generates a stream of effluent that includes fine metal particulate from the parts, fine ceramic particles from the finishing media, and the soap and lubricating oils from the steel-cutting process upstream. The suspended solids in this effluent are what differentiate it from other types of byproducts for purposes of disposal in the municipal sewer serving the company. As a result, Line Tool & Stamping Co. disposes of the effluent using a method that many companies with similar effluent have traditionally used: evaporation.
A large gas-fired machine was previously used to heat the effluent and accelerate evaporation. “It was a costly thing because before what would happen was that it would take three days to bubble off a day’s worth of production water,” Panico points out. “You had to run the thing constantly. It was a tough process to quote to [my customers] because you’re a slave to a commodity. If the cost of the gas went up, I would absorb the cost. The type of companies that I deal with, they give me a purchase order, and I price it. I can’t go back to them and say that the price of gas went up and I need more money—they won’t do business with you that way.”
Although the old evaporation process was not particularly labor-intensive, Panico says that the evaporation machine was repair-intensive. “Where I think it cost more money was in the actual maintenance of the machine,” he says. “You had moving parts; you had an electric motor on it, as well. There were thermostats and other gauges on it, and it was in a dirty, hot, damp environment, and many times we had to replace things on that machine.
“My evaporator was on—I won’t say its last legs—its last toe, so I went to the distributor that sold it to me, the ones who sold me the finishing [media]. They had been trying to get me to convert for quite some time, and I resisted because I figured I wouldn’t spend the money any sooner than I had to. When my list of alternative treatments started to dwindle and I couldn’t run the evaporator anymore, I purchased a wastewater treatment system.” The new turnkey system from Oxford, MI–based Wastewater Engineers Inc. was installed in 2007 and allows the company to recycle 100% of its process water and dispose of solid byproducts without the need for special handling.
Mass Finishing Effluent
From an environmental standpoint, the effluent generated in this type of wet finishing process presents challenges. The EPA has identified 40 toxic chemicals that can cause harm when they leach into the groundwater, including the ones generated from metal finishing at a company such as Line Tool & Stamping Co. For purposes of determining if the volume of these chemicals released into landfill leachate would produce environmental harm, the EPA developed a protocol known as the toxicity characteristic leaching procedure (TCLP). If the amount of these chemicals released under test conditions exceeds regulatory limits, the waste qualifies as hazardous and must be handled according to regulations governing hazardous waste, such as handling by certified disposal agents and recycling or disposal in specially designated landfills and incinerators. These practices can be very expensive, and conventional onsite treatment practices have proved both ineffective and costly.
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| Treated process water is pumped to a holding tank, where it is recycled back into the finishing process. |
Unlike such manufacturing processes as metal cutting and grinding, mass vibratory finishing generates extremely fine solids, so fine that they stay suspended in the effluent rather than settling to the bottom and lending themselves to clarification. Moreover, these particles are so tiny that filters used to capture byproducts from metal cutting and grinding do not trap the particles effectively.
Soft media, such as the ceramic clay media that Line Tool & Stamping Co. uses, also produce a higher volume of byproducts than that produced by harder media, such as steel. This high volume can saturate water in the effluent, decreasing its ability to suspend the solids and causing buildup of byproduct solids on production equipment. If the effluent is not discharged from the vibratory equipment in a timely fashion, a buildup of byproduct solids can compromise equipment performance and preclude disposal into a municipal sewer system.
“What people who cut ceramic tile don’t realize is that an awful lot of solids are given off as a byproduct of the process,” Wastewater Engineers President Chuck Case says of a manufacturing process that generates a volume of suspended solids similar to that generated by Line Tool & Stamping Co. “The same thing is amplified in a production situation—day in and day out with the same type of solids. By percentage, about 85% to 90% of the solids will settle out in water, and 15% to 20% of those solids will be suspended in water.” If left untreated, byproducts from metal mass-finishing operations pass through sewage treatment without being degraded by bacteria and accumulate in soil and rivers, contaminating animal species that cannot properly digest the metals.
In many mass-finishing operations, washing parts before smoothing them out is cost prohibitive, and the finishing equipment doubles as washing equipment. The finishing equipment can accumulate a residue of oil that was used in machining that occurred upstream. Not only can the oil residue adversely affect the performance of the finishing equipment, but it also makes the effluent unsuitable for discharge into a sewer system.
Another reason effluent from this type of finishing operation is not suitable for discharge directly into a municipal sewer is the typical high demand on oxygen in the sewer system to break down the effluent. Because vibratory compounds such as rust inhibitors are composed of amides, amines, and surfactants with high oxygen demands, the effluent most likely is above the allowable threshold for direct discharge into a sewer system.
Many manufacturers have used the evaporation method previously employed by Line Tool & Stamping Co. to manage their effluents. Besides the inefficiency and high-energy costs that are likely inherent in this process, other potential pitfalls exist. First, the manufacturer should avoid dispensing high-pH effluent to the evaporator because the steam gets exhausted to the atmosphere. Additionally, if large solids are not separated from the effluent prior to evaporation, they can agglomerate in the heating chamber and create a formidable cleaning task.
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| After parts undergo finishing, they are sent to a drying machine. |
Case argues that using ultrafiltration creates a situation not unlike the one Line Tool & Stamping Co. dealt with when utilizing evaporation: The filter membranes struggle to keep up with the volume of pollutants in a high-volume production scenario. Other shortcomings of ultrafiltration include its inability to remove dissolved metals, the presence of which usually makes the effluent unsuitable for sewer discharge; the high cost of replacing membranes that quickly clog; and the need to haul away separated solids from initial filtration and backflushing. “Most folks who have tried to get a small-enough micron find that the ultrafilters will clog rather quickly, and, therefore, it’s not as cost-effective as, say, a washer, where you’re taking out oils and gross suspended solids. The particles plug that ultrafilter rather quickly.”
Other methods of treating this type of effluent have been used, including settling and centrifugation. The main drawback of these methods is their inability to separate fine suspended solids, which, in a short time, can build up on manufacturing equipment. Settling uses a series of baffled tanks that remove larger particles; however, this process does not filter out smaller suspended solids or treat dissolved metals or oils to the point of suitability of disposal to a sewer. Centrifuges separate substances of differing specific gravities via centrifugal force as they spin on an axis. This process fails to separate smaller suspended solids; additionally, a non-automated centrifuge might cost as much as $10,000, and an automated unit that discharges once full might cost as much as $40,000. Polymers have been added to the centrifugation process to remove fine suspended solids, but this is another expensive component on top of the cost of the equipment.
Going Zero-Discharge
Another consequence of globalization is that, increasingly, major automakers and other industries are requiring their suppliers to comply with the environmental stewardship standards of ISO 1401. Recycling the process water can be not only compliant with international standards and environmentally responsible but profitable as well. Panico points out that before Line Tool & Stamping Co. had the new effluent treatment system installed, the finishing process required a constant supply of potable water during production. The process now recycles the process water while eliminating the high-energy costs of evaporation.
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| Line Tool & Stamping’s effluent treatment and water recycling equipment |
The first stage of the recycling system installed by Wastewater Engineers utilizes a dump/lift station equipped with an onboard, float-activated sump pump. Effluent from the finishing process fills a sump whose 2 cubic feet have been designed to prevent solid material from settling. As fluid accumulates, the float sensor activates a sump pump that transfers effluent to a 175-gallon collection/settling vessel with a 45-degree, conical bottom. A discharge gate valve located at the bottom of the collection/settling vessel allows gravity discharge of large solid matter into a filter cart located directly below. The filter cart is equipped with a large filter bag, a support basket, a fluids sump, and a discharge sump pump. After the filter bag traps solids, it transfers water back to a reactor.
The reactor has two parts: a mixing chamber with a conical bottom for liquid and a gravity-bed filter located directly beneath the mixing chamber. The operator pushes a button on a control panel that draws effluent from the upstream collection/settling vessel via an air diaphragm pump. When the 100-gallon level is reached in the mixing chamber, the operator starts a turbine mixer and adds a proprietary flocculent chemical to the liquid in the collection/settling vessel. The liquid and flocculent are mixed until a countdown timer control expires and the liquid and remaining suspended solids, dissolved metals, and oils are converted into a filterable agglomeration or floc.
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| The finishing machines use ceramic clay finishing media to smooth out rough
edges on the metal parts that the company manufactures. |
According to Case, the flocculent encapsulates solids and oil residue in the floc, preventing leaching and making the floc suitable for disposal in the trash farther downstream. The flocculent is formulated to leave intact any intentional additives to the production process that wind up in the effluent, such as rust inhibitors or chelating additives that attract dissolved metals to facilitate surface polishing or burnishing. The flocculent is also formulated to not have a major effect on the pH of the water, and it can be used in effluent with a pH between 6.0 and 10.0.
Case notes that the feasibility of using the treatment system depends on a couple of factors in the finishing operation. If the effluent has a high bacteria population that is indicated by a foul odor, it may be necessary to add bactericide or treat the liquid and add an odor-eliminating treatment. In addition, the metal-finishing effluent should not be commingled with other effluent in the storage, treatment, or recycle vessels because one will likely compromise the ability of the other to be recycled.
Following the flocculation stage, the operator opens a discharge gate valve on the reactor once per shift, and the contents of the mixing chamber flow down to the gravity-bed filter, where the toothpaste-like floc is captured by filter media made of a paper roll that is stretched across an auto indexing bed. Alternatively, the discharge gate valve can be equipped with an air-actuated valve and programmable timer for automatic “burping” of the floc. Once enough floc accumulates on the filter media to activate a float switch, a drive motor starts and pushes the auto indexing bed forward, depositing the floc into an adjacent sludge gondola. The treated liquid is discharged through a final canister filter and in a 300-gallon recycled-water holding vessel equipped with a pump for diverting the recycled water back to the mass-finishing equipment. The entire process of treating 100 gallons of effluent takes about 25 minutes, during which the operator is present for 10 minutes.
Besides separating suspended solids and dissolved metals, the flocculent removes up to 3% total oil from the effluent. For effluent with a higher percentage of oil, coalescers or skimmers are available to remove a higher volume. Emulsified oils (i.e., those that are engineered to combine with water) can be encapsulated by the flocculent if the oil-water bond is weak and may require the use of pretreatment chemicals for capture by a coalescer or skimmer.
When Line Tool & Stamping Co. was exploring new ways to treat its effluent, Case calculated that calling a hazardous materials specialist to dispose of the effluent would have cost $0.30 per gallon. The new treatment system yields savings beyond the hauling costs, however. The rust inhibitor that the company uses in its finishing process costs about $0.16 per gallon. The flocculent, which costs $0.08 a gallon, preserves virtually all of the rust inhibitor for reuse in the recycled liquid; this eliminates the $0.16-per-gallon cost of an additional inhibitor that would be added to potable water for metal finishing. So the company is spending about $0.08 a gallon to treat and recycle the water versus about $0.46 a gallon to have it hauled away—a more than 80% savings.
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| One treatment aspect is a chemical that flocculates fine solid material. |
Panico reports that the cost savings of using the new process are significant. “We’re probably using somewhere around $1,000 less in natural gas costs per month,” he says. “Number two, we’re not putting carbon emissions into the atmosphere, because then we were burning it off, and we had to funnel it outside. The other thing is that we’re using a lot less water—before, we were running water and soap through the machine constantly, whereas now we fill the tank once with water, and you need to drain the water maybe once every three months. My guess is that I saved myself probably $500 to $600 a month in water.
“I would say on any given month, it could be a little less, a little more, but I would say that, conservatively, we save anywhere between $900 and $1,100 a month between the cost of water, the cost of natural gas, and the cost of soap.”
The fact that the new process is a turnkey system also benefits the company, Panico adds. “The other thing is fewer maintenance costs. There are very few things that can go wrong with the equipment. There is basically a mixer and a couple of motors with pumps on them—that’s the extent of the moving parts.
“It took them about half a day to train us,” Panico continues. “Anytime I replace a piece of equipment, it’s got to be as hands-free as possible because today the manufacturing environment is so fiercely competitive that you’ve got to cut out as many steps as you can to try to be lean, even in the ancillary areas—not just in the actual production and manufacturing process but also in your secondary processes.”
Don Talend of Write Results, West Dundee, IL, is a public relations and communications consultant with a background of more than 15 years working in the media.
OW - January/February 2008
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