September 1, 2009
Shop owners who cut with waterjet machines should keep abreast oflocal waste and disposal regulations.
For many first-time owners of abrasive waterjet systems, the question of whether they will be dealing with hazardous waste in either the abrasive or the water looms large. Companies don't want to expose themselves to huge disposal or treatment costs, or face fines or litigation.
Because of the numerous levels of government in the U.S. and all of the materials a waterjet can cut, shops should keep abreast of current local solid-waste and water disposal regulations—and know the business and environmental costs of what they're throwing away.
The toxicity characteristic leaching procedure (TCLP), a key test for used water and abrasive, determines the toxicity of waste. Developed by the EPA, the TCLP simulates the leaching waste undergoes if it's disposed of in a sanitary landfill. It essentially determines how much, if any, of the toxicity characteristics will leach from the waste and enter the environment. If you will be purchasing a water softener, reverse-osmosis system, or water recycling system, the equipment supplier also should be willing to provide this testing service to you at little or no cost. For abrasive, ask your waste hauler whom it uses for TCLP. Your waste hauler performs this test at least once a year anyway.
"While less than 5 percent of waterjet users might be at risk of putting hazardous waste down their drain, it is worthwhile to verify that you are in the 95 percent group," said John Frosheiser, president of Custom Service and Design, a filtration supplier in Auburn Hills, Mich. "If you are in the 5 percent minority, it is important to know that there are ways to protect your company's interests."
First, get your water tested, and ask your local water utility for a listing of limits for heavy metals (see Figure 1). You can either check out the utility's Web site or simply call. Research about local practices is paramount, because the rules can change from municipality to municipality.
Now comes the chicken-and-the-egg problem: If you are a first-time waterjet user, you have no water to test before buying a system. You may have an idea of what materials you might be cutting, but certainly not the entire universe of materials, especially if you run a job shop. In this situation, try to take a sample of water from your waterjet supplier when you are having production cuts done. Simply gather a sampling of the overflow water and have it tested. If you find that you are near or above local limits, you have a number of options, such as filtering the water before it goes down the drain.
With waterjet cutting, you are pulverizing the cut material and not structurally changing the material like with electrical discharge machining (EDM). Therefore, most of the impurities in waterjet overflow water are suspended solids, not dissolved.
"Because waterjet cutting doesn't leach material like EDM, installing a simple settling tank prior to the drain is the oldest and best form of filtration," said Frosheiser. For most, this is enough to get the water within acceptable limits.
Settling tanks also help keep sewer lines clear. Over time enough suspended solids can settle out from your wastewater to block or restrict the sewer lines. If the municipality traces this back to you, you could face a large cost to cover the cleaning of the lines. So, be a good neighbor and put a settling tank inline. They are inexpensive to build or buy and simple to maintain.
If you are still uncomfortable with what you are putting down the drain, a closed-loop water recycling system may give you peace of mind. In some localities, it is the only solution. Such a system uses a series of filters to clean the overflow water from the waterjet. After going through the system, the water is pure enough to be sent back to the high-pressure pump for reuse in the waterjet process.
Garnet, the typical waterjet abrasive, is an inert, naturally occurring, semiprecious mineral It is either mined out of the mountains of upstate New York or Idaho, or shoveled off of beaches in Australia or India. Abrasive suppliers have material safety data sheets (MSDS) for garnet that typically can be downloaded from their Web sites.
So, is used abrasive hazardous waste? It depends on what you're cutting and how much.
"If you are cutting lead or beryllium copper, then you may have a hazardous waste situation," said Alan Bennett, market manager for garnet supplier Barton Mines Co., Glen Falls, N.Y. "For most other materials, the amount of the scrap material in the abrasive is so small that it is rarely a problem. Even most stainless steels are usually not an issue unless they contain a high nickel or chrome content."
Like with water, you should conduct a TCLP for the abrasive. If you can't get a sample of used abrasive before purchasing the machine, run the system for a couple of months and have that tested.
Disposing of used garnet isn't free, and costs add up over time.
"Because of the density of abrasive, reducing transportation distance is vital to reducing this cost," said Bennett. The shorter the distance your waste needs to be hauled, the lower your cost will be.
Behind many waterjet job shops sit several bulk bags of used abrasive piled up, draining water. They're draining as much water as possible from the abrasive so they don't have to pay for the disposal of water as well. Alternatively, a shop can invest in abrasive removal systems that drain off most of the water from the abrasive while it is being removed from the waterjet catcher tank.
Another abrasive disposal option: Sell it. Companies that make pavers, for instance, may pay you to take used abrasive off your hands, if you can send a consistent and significant supply.
Abrasive recycling may be another option depending on how much abrasive you use. Recycling systems can be costly to run and maintain, so this must be balanced against the savings. Some claim anecdotally that they actually get faster cutting speeds with recycled abrasive because it has been crushed during the cutting process, in essence giving each particle a sharp edge.
As Frosheiser put it, "The difficult thing for anyone is that all these [disposal] regulations are determined by local authorities, not even at the county level."
As just one example, some municipalities may allow your abrasive to be classified as a "byproduct" rather than "waste" and give you a lower rate for hauling it away. Being a good environmental citizen—knowing that what you're throwing away is environmentally safe—is important enough. But without knowing local regulations like this, you're leaving money on the table.
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