Guide to Washwater Re-use

A Guide to Water Reuse in the Carwash Industry

Reclaiming or reusing water in the Carwash Industry often gets bad press because of misconceptions in the technology and the process. The most common complaint from wash owners and their customers is the quality of the water. Typical reclaim systems include underground settling tanks and either an automatic backwashing filter or a Centrifugal separator system. In centrifugal separation, centrifugal force is used to separate solids from the liquid stream Separators are often used together with a filter as a pre treatment to remove larger particles from the water stream Automatic Backwashing Filters are designed for applications that need a constant quality of water delivering this style of filtration will ensure that the quality of water will remain constant no matter what type of particles are passed through the filter.
 

These systems were designed to reduce total suspended solids. The treated water is then re-used in the initial wash cycles in the process with no harm to the cars being washed or downstream equipment. The water however is still visibly dirty and contains oils/ detergents/ dissolved solids and other contaminants making the water unusable or undesirable in the rest of the wash process.

The truth is most process water (carwash and others) can be treated and re-used. Its knowing what is “in” the water and how to get it out. Different technologies exist for reclaiming and re-using process water. This article will help in understanding reclaim water in a carwash and options to achieve the water quality goals.
 

Keep these few points in mind as you read through this article:

1. Look at the recovery and re-use of Carwash water as a “process”. There are different technologies that will be applied depending on the conditions of the feed water and the quality of the process water desired.

2. Each Carwash is “different”. Many factors go into the design of a solution that works for each wash. Factors to consider in the design other than the feed conditions or quality of water desired may be space constraints, chemicals used, process flow, flowrates and pressures to name a few.

3. In some cases other technologies exist that can be applied to certain water quality problems, for the purposes of this article we have limited them to the equipment discussed below.

4. Don’t be intimidated! The re-use and reclaim of water may seem difficult, however the process is simple. Identify what is “in” the water to be treated and then applying the right technologies to remove it. 

Know the problem

Know the problem. Identify what you want to achieve with your reclaim process. Maybe you have usage restrictions or discharge issues, or rising water and sewage costs. Maybe you are not happy with the water quality, or you have downstream equipment maintenance issues. The importance here is that there are different levels of water treatment depending on the usage or discharge. Whatever the reasons, understanding what you are trying to accomplish has an impact on the approach to the process and design. 

The Water

Carwash Process Water is unique in that it will be different in each location. Generally what is in the water is similar in all Professional washes, how much of each is the problem. Environmental differences, owners preference to soaps/conditioners, and feed water quality are some of the reasons they are different. An improperly installed or the lack of maintenance of the settling tank system further erodes the quality of the water to reclaim. 

A water analysis should be taken of the water to be treated. Additionally it should be noted at what point the sample is drawn. Was the settling tank just pumped? Is it winter, when road salts are used? These questions and others help in identifying the technologies that should be applied to the design. Another important consideration is the products used in the wash. Once something is identified in the water, it’s possible that it is introduced via the products used. Finding alternatives can eliminate having to treat to remove them.

The Process

In understanding the design of the carwash reclaim process it helps to know the wash equipment and how it operates. Differences in the wash equipment and the quality of water that can be used in each step of the wash will help in designing a balanced and efficient system. In addition you will also want to consider the other uses of the water at the carwash. Chemical mixing, irrigation, and facility maintenance can have an impact on options in the design and use for the reclaimed water.

The filtration process to reclaim carwash water starts at the floor drains or drainage system prior to the settling tanks. This is where large debris is captured and removed prior to discharge to the underground settling tanks. The underground settling tanks rely on gravity and naturally occurring biological activity and improves the water to be reclaimed. Proper tank maintenance goes a long way to achieving the best results in recovering and reusing water at a Carwash. It helps to regulate what is going into the rest of the reclaim process and should be periodically pumped to maintain performance. 

Volumes can be written about the design on the drainage and tanks, but we will leave that for another discussion and jump to the process and equipment used in reclaiming water. The design of the reclaim process can be decided based on customer preference on the water quality at each application of the carwash. Depending on these factors, appropriate technologies applied in the proper sequence will be needed to meet the criteria. 

The Technologies
There are many technologies that can be applied in the recovery and re-use of carwash water. Each technology has pros and cons to their use and some can even be applied at different stages in the process. 

A brief overview of some of the equipment (technology) applied in the carwash water reclaim process follows. Other choices in technologies exist, and can be addressed in the design.

- Automatic Backwashing Filters or Particle Separators – Used to reduce suspended solids in the water. These systems typically remove solids down to 25 microns and can be used in the initial stages of the wash. Washes have traditionally used this water for presoak, tire, undercarriage and even the in the application of soap to the car. Although the sediment has been reduced in size down to 25 microns the appearance of the water is a darker grey.

- Oil/Water Separator - Oil and grease removal is necessary to protect membrane based technology downstream of the process The oil/grease content of the reclaim water must be less than 10 ppm for UF Technology and less than 1 ppm for Reverse Osmosis.  Anything higher risks fouling the membranes. Typical oil water separators are tanks designed with compartments and baffling. As the water enters the chambers the oil starts to rise to the top and is skimmed out. If the oil/grease is content of the water is primarily emulsified a different treatment process may be required.

- Ozone Generation -   Ozone can be recycled into the underground settling tank to oxidize organic solvents, sulfides, odors, and heavy metals. This helps in maintaining pit performance and improves the aesthetic quality of the reclaimed water. (a much lighter shade of grey)

- Ultra filtration - Ultra filtration is a low-pressure membrane process, capable of removing, bacteria, virus, suspended solids and large organic materials. The filtrate water from the ultrafiltration system can be used in the wash, final rinse, chemical mixing, and as feed to the reverse osmosis spot free rinse system.

- Flocculation – This process consists of a contact tank and the dosing of a flocculant agent into the process. The flocculant (like Alum and others) help to bind together the suspended solids of less than 25 microns in the water and gravity settles it to the bottom of the contact tank to be discharged. (flocculation will only be used if the  volume of suspended solids less than 5 micron exceeds recommended limits.

- Chemical Dosing – Chemical dosing may be applied depending on the condition of the water. If the water is high in biological content that a method for control might be chlorine dosing. Usually dosing is only applied when conventional technologies are not effectively handling the load.

- Reverse Osmosis – Reverse Osmosis is used to remove Total Dissolved Solids from the water. Typically Reverse Osmosis removes 98%+/- dissolved solids content. Permeate TDS levels of 40 ppm or less is considered spot free water. Reverse Osmosis is also a membrane based system that splits the water into two streams. The permeate stream is stored ready for use when the carwash calls for it. The Concentrate water can also be used in the wash or returned to blend with the reclaim water in the beginning of the process.

Conclusion

As mentioned earlier in this article there are other technologies that can be applied in treating the water in the Carwash Process. The equipment described above best illustrates the technologies required to take the leaps in water quality desired. These technologies have been around for years and have proven effective in treating many types of process water. Since locations and feed water characteristics differ so does the process flow and equipment used to treat the water from Wash to Wash. 

Starting down the road to Reclaim and Re-use of the process water from a carwash as mentioned is the expectations from the system. This is important in determining the technologies to apply. Another important note to review is the quantity and ingredients of the soaps, detergents, and protectants used in the wash. All this adds to the water to be treated.
 
The benefits of reclaiming water range from the reduction of fresh water required into the carwash, cost of water and sewer, and perception about the wash and water quality. Environmentally you play an important part in con-serving water for future generations.