Environmental Engineering Reference
In-Depth Information
automatic washes to 66-85 gal per vehicle for conveyor type washes.* Carwashes that con-
tain reclaimed systems—systems that separate grit, oil, and grease from wash and rinse
water and then filter it for reuse—can reduce water use by more than half. Although, even
with a reuse system 10-20 gal of makeup water is needed per vehicle washed. According
to a recent study on Phoenix carwashes, water losses can additionally occur through
evaporation and fine mists, especially in warmer areas or during hot periods in Arizona,
and those losses have been estimated to range from three to seven and one-half gallons
per vehicle.
Water-efficient measures should be required of all individual carwash facilities pro-
posed for any site along with the need for all facilities to reuse as much water as pos-
sible. Harvested rainwater from adjacent individual buildings and associated pavement
could be used to supplement water for a carwash. If a permeable pavement is chosen,
the water filtered by the pavement could be harvested and reused for a carwash makeup
water system. This would allow the pavement to capture most solids instead of requiring
a separate first-flush system. Carwash reuse systems require the used, silt-laden water to
pass through three settling tanks before reuse; therefore, if a little silt is in the harvested
rainwater (makeup water), it will be filtered out in the typical carwash water reuse process.
The final rinse will typically be a reverse osmosis process initiated with clean municipal
water, which is required for reducing water spotting, but the basic wash cycle can include
harvested rainwater. The use of rainwater has the added benefit that it is naturally soft
water and will potentially allow a carwash to use less soap. Use of harvested rainwater
will assist in reducing the demands placed on the municipal water supply.
21.5.3.2 Water Losses and Reuse by Mechanical Equipment
Cooling towers use a significant amount of water to maintain the air-conditioning/cooling
process. Cooling towers have been identified as often being the largest single user of water
in commercial and industrial buildings. The basic function of a cooling tower is to use
evaporation to lower the temperature of water that has been heated for some building
operating process. Cooling towers typically lose water in three ways: evaporation, bleed-
off (or blowdown), and drift. All of these losses are replaced with makeup water. The
evaporation process involves the main cooling component while the bleed-off water flushes
the high concentrations of total dissolved solids (TDS). The drift is uncontrolled water loss
in the form of mist or droplets carried away by airflow or winds. Some additional loss may
occur through valve leaks or draw downs for various miscellaneous uses. Makeup water
replaces all these possible water losses in a cooling tower.
In most cooling towers, the primary opportunity for conserving water is to reduce the
amount of makeup water required to replace bleed-off water. In order to use harvested
rooftop rainwater as makeup water for the cooling tower, the rainwater constituents would
need to be determined. The TDS and individual dissolved constituent would affect the
chemistry in the cooling tower operating water and adjustments might need to be made.
Most solids could be settled or filtered out of harvested rooftop rainwater leaving the dis-
solved content as the issue for reuse. Rainwater for makeup water should be disinfected
with ultraviolet prior to use. In some areas the large quantity of makeup water cannot be
met by the collected rainwater and the opposite situation could be conducted; i.e., instead
of using rainwater for a cooling tower, the blowdown water from the cooling tower could
be added to the rainwater supply to increase alternate water for building water needs.
*
http://www.hanna-sherman.com/water-chem/reclaimII.html (accessed April 30, 2003).
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