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Self-serve's spot solution

October 11, 2010
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The quality and volume of water that your carwash uses as well as where you get the water and how you use it are as important as any other factor in the planning process.

Why spot-free?
A good quality wash ends with a spot-free car, and many customers are willing to pay a little bit more for a quality wash.

A spot-free rinse system, or reverse osmosis system is primarily used at the end of the process for a final rinse. At the self-serve wash, it is selected as one of the last functions on the control panel.

Spot-free water processed through a reverse osmosis system is low in mineral content, which is measured as total dissolved solids (TDS).

Water containing less than 30 TDS will produce a fine quality rinse.

Treat the water
Water treatment or pretreatment is the first factor when considering a spot-free system for your self-serve. Since most carwashes are plumbed to a city water source, many feed water quality issues have been eliminated.

However, depending on the location of the carwash, water hardness may be a concern. Hard water, over time, can clog pipes and spray nozzles, degrade pumping performance, and produce a poor quality wash.

It also reacts poorly with soaps and detergents requiring higher concentrations to produce desired results. For the spot-free rinse system it will scale the membrane reducing production and eventually clog the membrane.

Another concern for a reverse osmosis system when attached to a city water supply is chlorine.

Chlorine, even at low doses, will disintegrate the material of the membrane and over time will allow poor quality water into the production stream.

Simple water softeners and activated carbon filters will correct the above problems. A water analysis should be done to correctly size the equipment necessary to protect the spot-free rinse system.

An additional 5 micron filter (usually standard with the system) provides added protection for potential debris that may get into the feed water stream.

The right design
A reverse osmosis system is simple in design. The main component is a thin film composite membrane.

Reverse osmosis uses a membrane that is semi-permeable, allowing pure water to pass through it, while rejecting contaminants that are too large to pass through the tiny pores in the membrane. The most commonly used membrane is 4” x 40” in the carwash industry.

The only other components necessary to make spot-free water are a pressure (pump) and a valve to create backpressure on the membrane. The rest of the components on the system are for operation and functionality.

Although it is not required to have all the options on many of the systems available today, each option adds certain benefits that pay for themselves in the long run. Below are some of the options and their benefits:

  • Low pressure protection — protects the pump if the water supply fluctuates;
  • Flow meters — help in properly setting up the system and monitoring performance;
  • Pressure gages, pre-filter/pump discharge/concentrate — for proper setup and troubleshooting;
  • Recycle valve — reduces the waste water stream to drain;
  • Auto restart — restarts the system when flow pressure returns;
  • TDS monitor/ quality indicator — monitors water quality;
  • Auto flush — high unrestricted flow across the membrane to reduce the potential of fouling, and;
  • Cold water membranes — lower rejection, but increased product water production for colder climates.

A spot-free rinse system also requires a storage tank for the permeate (product water), level controls (tank full condition) and a pump to send the water to use.

Pressure and the RO system
A typical system for a self-serve carwash is designed with one or more 4” x 40” reverse osmosis membranes.

A 4” x 40” membrane needs 5 gallons per minute (gpm) of waste (concentrate) water.

A good option to purchase with the system is a recycle valve, which will take some of the wastewater and blend it into the feed system to reduce the amount of water going to the drain.

A common misconception in reverse osmosis is operating pressure. Although it is the backpressure on the membrane that produces spot-free water, it’s the flow that is the most important factor in correctly adjusting the system for operation.

The operating pressure for the spot-free rinse system is achieved once you get to 1 gpm of permeate (product) water.

Some systems have recycle valves and pump throttle valves. At start up or occasional adjustment periods it will be necessary to fine-tune all three valves for desired operating flows.

Start closing the concentrate valve until 1 gpm of product water is achieved. Then you can adjust throttle and the recycle valve until you get the proper recovery of wastewater. The pressures will change as you adjust the valves.

A good operating condition would be at 50 percent recovery, meaning 1 gpm of permeate water and 2 gpm of concentrate water. When operators exceed the 1 gpm of product water per 4” x 40” membrane it is reducing the life of the membrane.

System maintenance
Periodic adjustments (when necessary) to the valves may be required due to service hours.

When the adjustments no longer affect the performance of the membranes, installing new membranes will be necessary. The system always comes with a 5 micron filter that may need to be changed monthly or when required.

A routine check for leaks is always a good idea on any equipment in the carwash. Correct leaks as soon as they are detected.

Reap the rewards
You are paying for city water so why not use it. The concentrate (waste stream) may be used in the rest of the carwash. Don’t dump into the drain.

Many operators have installed a second storage tank to catch the wastewater. This water can be used for irrigation or be redistributed in the carwash.

A simple level control, solenoid, tee to feed water supply and re-pressurization system can be hooked up to blend the water back into the carwash.

Another good use for the spot-free water is building maintenance. Spot-free water is great for windows, chrome, or any shiny surface.

Mixing chemicals with reverse osmosis water will increase the chemical performance of all detergents and cleaners.

Spot-free rinse systems, when sized, purchased, and operated properly enhance the business in many ways. The systems of today have been designed for many years of trouble free operation and produce happy customers and operators.

Jim Keller is the president of Con-Serv Manufacturing in Lakeland, FL. Keller is also a 43-year veteran of the carwash industry and a manufacturer of water treatment and wastewater recovery systems for the past 30 years.

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