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Guide to Washwater Reuse
Coming Clean on Carwash Reclaim Water 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 theprocess. The most common complaint from wash owners and their customers is the quality of the water. Typical reclaimsystems include underground settling tanks and either an automatic backwashing filter or a Centrifugal separator system. Incentrifugal separation, centrifugal force is used to separate solids from the liquid stream Separators are often used together witha filter as a pre treatment to remove larger particles from the water stream Automatic Backwashing Filters are designed forapplications that need a constant quality of water delivering this style of filtration will ensure that the quality of water willremain 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 reused in the initial wash cycles in theprocess with no harm to the cars being washed or downstream equipment. The water however is still visibly dirty and containsoils/ detergents/ dissolved solids and other contaminants making the water unusable or undesirable in the rest of the washprocess.
The truth is most process water (carwash and others) can be treated and reused. Its knowing what is “in” the water and how toget it out. Different technologies exist for reclaiming and reusing process water. This article will help in understandingreclaim 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 reuse of Carwash water as a “process”. There are different technologies that will be applieddepending 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 inthe 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 articlewe have limited them to the equipment discussed below.
4. Don’t be intimidated! The reuse 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 ordischarge issues, or rising water and sewage costs. Maybe you are not happy with the water quality, or you have downstreamequipment maintenance issues. The importance here is that there are different levels of water treatment depending on the usageor discharge. Whatever the reasons, understanding what you are trying to accomplish has an impact on the approach to theprocess 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 allProfessional 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 thesettling 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. Oncesomething is identified in the water, it’s possible that it is introduced via the products used. Finding alternatives can eliminatehaving 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 abalanced and efficient system. In addition you will also want to consider the other uses of the water at the carwash. Chemicalmixing, 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 iswhere large debris is captured and removed prior to discharge to the underground settling tanks. The underground settlingtanks rely on gravity and naturally occurring biological activity and improves the water to be reclaimed. Proper tankmaintenance goes a long way to achieving the best results in recovering and reusing water at a Carwash. It helps to regulatewhat 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 tothe process and equipment used in reclaiming water. The design of the reclaim process can be decided based on customerpreference on the water quality at each application of the carwash. Depending on these factors, appropriate technologiesapplied 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 reuse of carwash water. Each technology has pros andcons 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 choicesin technologies exist, and can be addressed in the design.
. Automatic Backwashing Filters or Particle Separators – Used to reduce suspended solids in the water. These systemstypically remove solids down to 25 microns and can be used in the initial stages of the wash. Washes have traditionally usedthis water for presoak, tire, undercarriage and even the in the application of soap to the car. Although the sediment has beenreduced 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 processThe oil/grease content of the reclaim water must be less than 10 ppm for UF Technology and less than 1 ppm for ReverseOsmosis. Anything higher risks fouling the membranes. Typical oil water separators are tanks designed with compartmentsand 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 ofthe 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. (amuch lighter shade of grey)
. Ultra filtration Ultra filtration is a lowpressure membrane process, capable of removing, bacteria, virus, suspended solidsand large organic materials. The filtrate water from the ultrafiltration system can be used in the wash, final rinse, chemicalmixing, 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 tothe bottom of the contact tank to be discharged. (flocculation will only be used if the volume of suspended solids less than 5micron exceeds recommended limits.
. Chemical Dosing – Chemical dosing may be applied depending on the condition of the water. If the water is high inbiological content that a method for control might be chlorine dosing. Usually dosing is only applied when conventionaltechnologies are not effectively handling the load.
. Reverse Osmosis – Reverse Osmosis is used to remove Total Dissolved Solids from the water. Typically Reverse Osmosisremoves 98%+/ dissolved solids content. Permeate TDS levels of 40 ppm or less is considered spot free water. ReverseOsmosis is also a membrane based system that splits the water into two streams. The permeate stream is stored ready for usewhen the carwash calls for it. The Concentrate water can also be used in the wash or returned to blend with the reclaim waterin 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. Thesetechnologies have been around for years and have proven effective in treating many types of process water. Since locations andfeed 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 Reuse of the process water from a carwash as mentioned is the expectations from thesystem. 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 conserving water for futuregenerations.
