What About Wash Water?
Recently, we have received several questions about proper ways to contain and/or treat wash water used to clean everything from muddy trucks to oily parts. Therefore, today we thought we would address two important questions: why does containing your wash water matter and what are some different solutions to address this issue?
First, let’s dive into the importance of containing or treating your facility’s wash water. Wash water can contain a variety of pollutants including sediment, oil & grease, and possibly chemicals. Without containment or treatment, the contaminated water can discharge off-site and into the surrounding environment, negatively impacting water quality and wildlife. For example, sediment increases the turbidity of water and can prevent fish from seeing food. Sediment in the water refracts light, interfering with the growth of aquatic vegetation. Oil & grease can deplete oxygen levels in water causing stress to organisms. Due to this, it is important to know what contaminants your facility has the potential to discharge. This knowledge will help your facility adequately treat and/or contain any contaminated water. For example, facilities washing only muddy equipment are mainly dealing with sediment as a pollutant. However, facilities using solvents or detergents to cut through oil & grease have the potential to discharge oil & grease, sediment, and harmful chemicals; solvents and detergents often contain chemicals that are detrimental to the surrounding environment. Additionally, the Environmental Protection Agency’s (EPA) National Pollution Discharge Elimination System (NPDES) permit for storm water associated with industrial activity does not allow certain types of non-storm water discharges, such as contaminated wash water. Therefore, in order to maintain compliance with a NPDES permit, wash water must be contained and/or treated. So, what are some ways to prevent the discharge of wash water in order to protect the surrounding environment and maintain compliance?
One of the most advanced options is a closed loop microbial water treatment system. In this method, all washing will need to occur on a graded concrete pad. The grade of the pad will force the contaminated water into a collection line leading to a two-part system. In this system, a plate clarifier separates solids from the water and the microbes consume the oil & grease. Then, this treated water is recycled and available for additional washing. This option is advantageous because it is a permanent solution that treats water contaminated with sediment and oil & grease. However, this system can be fairly expensive and typically must be kept indoors.
A settling tank could be employed as a solution to removing suspended particulates from water. In this system, contaminated wash water would be directed to a large tank. Similar to the first approach, washing would occur on a graded pad. The design of the pad would force water to a collection line leading to the tank. The high velocity of water exiting a hose or pressure washing system causes particles to be suspended in the water. Once the water enters the tank, the velocity will slow. As the water slows and travels through the tank, gravity causes particulates to settle. The tank would need to be cleaned periodically as sediment builds up. This system is advantageous because it is a relatively simplistic process. However, this tank would only remove particulates from the water while leaving any other contaminants such as oil & grease.
A standard oil water separator could be used as another simple solution to treat wash water. All contaminated water would need to be directed into the system through a graded pad and line. The advantages to this solution are the comparatively low cost, simplistic installation, and prevention of oil & grease discharges to the environment through storm water. However, this system would only address oil & grease and eliminate the ability to use detergents or solvents as these solutions are typically water soluble and not permitted to be discharged.
Another approach is an oil water separator with water elimination. In this approach, all washing would be conducted on a concrete pad with an additional layer of filter material underneath. This filter material would protect the underlying soils and groundwater from contamination if the concrete cracks. The concrete pad would be graded in order to direct all wash water to a collection line. This line would feed the water into an oil water separator with a mechanism to discharge the excess water as water vapor, leaving only the oil. The facility would only be responsible for disposing drums of oil. This solution would help eliminate the potential contamination from detergents and solvents as they are generally water soluble.
Clearly, there are a variety of options for constructing a containment or treatment system for wash water. We hope this brief overview of different solutions will help you find a solution that will meet your needs and budget. As always, if you have any questions or want more information, please do not hesitate to contact VET at (812) 822-0400. Stay healthy!
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