Best Management Practices & Pollution Prevention
Printers can become part of the solution by doing the following (some of these may be requirements based on state/federal regulations):
Improve production methods by coordinating runs according to color, type or quantity, thereby reducing the number of cleanups.
Soiled shop towels may contain hazardous or volatile solvents and residues. To reduce the risk of fire and control fugitive VOC emissions, soiled shop towel storage containers must be kept closed at all times.
Observe good cleaning practices by only using enough solvent to get the job done.
Closely manage the dispensing and storage of solvents and towels/wipes.
Separate excess solvent from towels/wipes using techniques such as gravity draining, hand wringing, mechanical wringing, and centrifuging. Recovered solvent can be reused and recycled.
Use alternative solvents that minimize hazardous waste and air pollution. For example, using cleaning solvents that do not contain any listed chemicals or those with flashpoints below 140°F and have a vapor pressure less than 10 mm Hg at 68°F are ideal).
Collect solvent waste for recycling.
Establish accountability for solvent use and waste generation.
Use water based inks, where applicable.
Shop towel centrifuge
Reusable Shop Towels
The effluent released from the spent towels at the laundry can become a concern to the sanitary system (i.e., sewer treatment) as the contaminants are washed out. It is the presence of inks and solvents that create problems for the industrial laundry and the community sanitary sewer system that handles the effluent from the laundry and most industrial launderers have set up treatment systems to minimize the impact of these contaminants.
In order to minimize the impact on water quality, control costs associated with shop towels, reduce VOC emissions and solvent purchase shop towels should be carefully managed on site. Excess solvent can be removed from used wipes by gravity separation, hand wringing, mechanical wringing, spinning in centrifuge or microwaving (typically provided by a service). Regardless of the method, the solvent extracted can be reused or recycled off site (see solvent recovery section).
Gravity separation involves placing the shop towels inside a closed container with a false bottom and permits the solvent to move down and out of the towels. A false bottom typically consists of a metal grate and/or drain at the bottom of the container that permits the solvent to move away from the shop towels. In order to extract the maximum amount of solvent for recovery this method should be combined with hand and or mechanical wringing, or centrifuging.
Hand wringing consists of hand squeezing the towels to extract the solvent. The amount of solvent extracted depends on the operator. Mechanical wringing consists of feeding the towels through a hand crank or electric powered wringer. These systems typically mount on the top of a 55-gallon drum. As the towel is wrung the solvent drips into the drum. The electric powered wringers must be equipped with explosion proof wiring.
A centrifuge is a mechanical device that spins an object to separate materials with different specific gravity. Centrifuging involves placing the shop towels in an industrial centrifuge where the towels are spun and the solvent is drawn out of the towels and collected. A centrifuge can extract 2 to 3 gallons of solvent from approximately 220 towels that have no free flowing liquids when placed in the centrifuge.
When installing a centrifuge, be sure to check local fire codes that may affect ventilation and electrical requirements. The centrifuge must be constructed using explosion proof wiring systems if used with flammable or combustible materials.
Microwave solvent extraction is similar to other types of solvent recovery technologies. The goal of the microwave system is to recover clean usable solvents from shop towels contaminated with ink and other contaminants.
The microwave recovery system is more versatile than traditional recovery systems. As can be seen in the diagram below, the microwave system works in a one-step process subjecting the print towels and blanket wash to intense microwaves that break the emulsion between the water and solvent. Breaking the emulsion allows the clean solvent to be recovered and reused without any additional processing. The recovered water and solvent mixture is collected together and then separated into separate containers. After being treated by the microwave unit, the soiled print towels are then ready to be laundered by a commercial laundry.
The wastewater, which ends up as “distilled water”, generally meets the local regulatory requirements and can be discharged to the local sewer authority. It is important to recognize, as with any discharge to a sewer authority, it is imperative to contact them to ensure the acceptability of the discharge. Discharges of industrial wastes to septic systems are generally prohibited.
Reusable towels contaminated with ink, solvent, or oil, that would be otherwise classified as a hazardous waste are not considered hazardous wastes under federal and most state regulations if they are not saturated and are laundered and reused.
Each state regulates towels differently and the printer must first comply with state regulations.
Users of disposable wipes need to be careful about how the used wipes are disposed of if they are to remain in compliance with regulatory requirements and minimize corporate environmental liabilities.
Used wipes may be subject to hazardous waste regulations if the wipes contain inks, solvents, oil, or residues that are classified as hazardous. Towels that are contaminated with materials that are classified as “listed” hazardous wastes must always be considered as hazardous and must be disposed of as such. Towels that are contaminated with materials that are classified as “characteristic” must either be handled as a hazardous waste or the printer can evaluate the towel and if it does not exhibit any of the characteristics of a hazardous waste, it can be classified as nonhazardous.
However, even if the wipes do not contain hazardous solvents or residues, it may not be in the best interest of the printer to dispose of their wipes with the rest of the trash. Contaminants that can leach out of the wipes at a landfill can expose the printer to expensive remediation costs if the landfill used for the towels becomes a Superfund site. There is no statute of limitations for liability. If disposable wipes are used, it is important that the printer has a documented, accurate, and comprehensive picture of all the solvents and residual contaminants that could remain on the used wipes.
For access to vendors who may supply alternative materials and equipment, see the PNEAC Vendor Directory.