Professional Carwashing & Detailing

In-bay reclaim done the right way

October 11, 2010

The issue of recycling water for reuse in commercial carwashing has come to the forefront as an important business decision because of rising water and sewer discharge fees. Recycling can help owners control operating costs.

Environmental regulations, along with restrictions and mandates for permitting also play a role in the need to recycle water.

Finally, the desire for good corporate citizenship is a factor from a consumer perspective that will help owners decide whether they need or even want to recycle used water.

Pre-treatment
Before considering recycling options, the fresh water supply must be evaluated and possibly treated before it is ready to use in washing equipment.

Many water sources have dissolved calcium and/or magnesium (water hardness) present at elevated concentrations that should be removed before being used in a wash.

These minerals can form scale deposits which will clog nozzles, decrease flow capacity of pipes and cause spotting on a car as the water droplets evaporate and leave the minerals behind.

They attach to the insides of piping, and create a condition, over time, that is very similar to hardening of the arteries.

Water softening effectively removes these minerals by a process known as ion exchange.

The system
Generally, in-bay automatic carwashes operate with two types of washing equipment: frictionless or touch-free.

Regardless of equipment used, a properly designed recycling system will be an integral component to the success and cost effectiveness of the operation.

The recycling systems baseline demand from either type of wash is straightforward;

  • Supply water free of large suspended solid particles;
  • Supply water free of odors; and
  • Supply sufficient pressure and volume to meet the demand of the washing equipment.

Suspended solids removal process
Small particles that are carried by the motive flow of water are considered suspended solids.

Typically, the high-pressure pumps being supplied by the recycling system have very tight tolerances and any suspended solids in the water will gradually damage the pumps internal components.

As such, most high-pressure pump manufacturers require recycled water to have less than 20 micron particles. Preferably, even tighter filtration is required, down to the five micron range.

There are several methods available to reduce the solids in water to the desired particle range size.

Particle filtration processes used to remove the suspended solids generally consist of

  • Surface filtration;
  • Depth filtration; and
  • Physical/chemical precipitation followed by filtration.

Effective approaches
1. Cartridges and/or bag filters along with screen type filters have proven effective in reducing suspended solids close to the desired range of less than 20 microns.

However, the dirt holding capacity of these types of filters is limited by the actual surface area of the filter media or septum. Solids are captured on the surface of the filter and accumulate there.

As the solids increase on the surface of the filter, the flow of water through the filter decreases, thereby mandating that the filters be cleaned or replaced.

Typically, cartridges and bag filters require much more maintenance, frequent cleaning and/or replacement of the filters themselves.

2. Depth filters are another effective approach. These filters, while larger in physical size, are well proven to remove suspended solids to the desired range and have the added benefit of increased solids holding capacity.

Typically, these filters have a bed of permanent filtration media with much greater surface area and dirt holding capacity. Depth filters are generally self-cleaning, using automatic back-washing valves to reverse the flow of water and wash-out the solids collected in the filter bed.

Less suspended solids in the water equates to less wear and tear on washing equipment and cleaner water for reuse.

Volume reduction
Using recycled water in an in-bay automatic will definitely reduce the amount of fresh water required by the washing equipment.

Recycled water is generally used in the high-pressure applications only. Chemical applications and the final rinse use fresh water and/or reverse osmosis water, respectively.

Frictionless washes generally use a much greater volume of water under high-pressure to accomplish the washing tasks.

Friction washes use much less water per car. There are no hard fast rules since each in-bay equipment manufacturer and each operator sets up their equipment to meet customer’s needs, but experience indicates that approximately 60 percent or more of the water used in all in-bay automatics is high-pressure.

Therefore, an owner can expect a volume reduction of fresh water use in the 60 percent or plus range with a corresponding reduction in sewer fees.

Cost and payback
It would not be prudent to purchase a recycling system based upon cost alone.

Factors associated with water and equipment needs should be the driving concern. Buying a $15,000 system that does not meet an owner’s needs would be far worse than spending $25,000 for a system that produces the water quality and volume requirements for that particular type of wash.

Commonly, payback is directly evaluated based upon the reduced cost of water and sewer fees due to overall volume reduction. However, other areas certainly come into play here as well:

  1. Equipment wear and tear: Deterioration due to poor recycled water quality definitely impacts any payback or savings.

    An owner won’t save money on water if he or she has to repair or replace the high pressure plunger pumps frequently due to damage caused by large suspended solids in the water.

  2. Facility maintenance: If a wash owner has to replace filter media, bags, or cartridges on a continual basis then the labor and cost of these replacement parts factors into the actual operating cost for these systems.

    In addition, the extra labor used to clean tunnel walls and washing equipment caused by poor quality recycled water is a real expense that should not be overlooked.

  3. Quality service: Finally, if the recycling system used impacts the equipment’s ability to produce a clean car, then the water and sewer savings really aren’t savings after all.

Post treatment
Recycling systems are designed to produce water suitable for use in the washing operations. The final rinse of the vehicle should be performed with a very high-quality water to eliminate the potential for spotting.

Typically, a reverse osmosis (RO) system is the choice of most operators whose water requires post treatment. In selecting an RO system for an in-bay automatic two questions should be addressed.

  1. What is the percentage of rejection of Total Dissolved Solids (TDS)?
  2. What is the water recovery percentage?

If you start with a raw water supply that contains 100 parts per million (ppm) TDS and the RO rejects 95 percent then the product water you will be rinsing cars with will have approximately 5 ppm TDS.

Percent recovery refers to how much raw water it takes to make a gallon of spot-free water. Most systems recover 50 percent, which means that it takes two gallons of raw water supply to produce one gallon of spot-free water.

The rejected water can be sent to the recycling system, however, in order to meet volume demands, the RO system that recovers 50 percent will have to be large enough to produce enough volume to meet an owner’s needs.

A better option is to select an RO system that has higher recovery rates, preferably in the 75 percent or plus range.

For every four gallons of raw water supplied to the RO, three gallons of spot-free are produced. Obviously, this is preferable from a raw water cost perspective and reduces the volume of reject water by 50 percent.


Robert Harvey is the director of engineering & support for Hydro Management Systems. He is a chemical engineer with 26+ years of experience in industrial water and wastewater treatment design experience. Robert can be contacted at purewater@mindspring.com.