Water is expensive to buy, treat, and dispose. If your firm does not have a water conservation program, you are pouring money down the drain.
A water conservation program can cut water consumption by up to 30 percent or more, and the cost savings can pay for the required materials in a very short time. For example, at average water and sewage rates of about $2 per 1,000 gallons, a reduction of the flow to the washers by just 1 gallon per minute can save $250 per year. Since the average plant has a large number of washers, the savings can add up to thousands of dollars per year.
Numerous methods have been developed to conserve water at textile mills. The sections below discuss some of the techniques applicable to a wide variety of firms.
For both water and energy savings, counter-current washing is employed frequently on continuous preparation and dye ranges. Clean water enters at the final wash box and flows counter to the movement of the fabric through the wash boxes. Thus, when the fabric enters the actual wash process, the most contaminated wash water contacts it first, and, later, the cleanest water contacts the cleanest fabric.
This method of water reuse is contrary to the traditional method of providing clean water at every stage of the wash cycle. Water and energy savings are related to the number of boxes provided with the counterflow. Counter-current washing can be applied at desize washers, scour washers, mercerizing washers, bleach washers, dye ranges, and printhouse soaper ranges.
The rinse water from the final rinse in a batch dyeing operation is fairly clean and can be used directly for further rinsing or to make up subsequent dye baths. Several woven fabric and carpet mills use this rinse water for dye bath make-up
Reuse of Soaper Wastewater
The colored wastewater from the soaping operation can be reused at the backgrey washer, which does not require water of a very high quality. Alternatively, the wastewater can be used for cleaning floors and equipment in the print and color shop.
The rinse water from the scouring operation is adequate for reuse in other processes such as desizing that do not require water of an extremely high quality. This reuse is particularly true with scouring wastes from synthetic or cotton/synthetic blend fabrics. Scouring rinses may, in certain cases, also be reused to wash floors and equipment.
Mercerizing or bleaching rinse water can be used in scouring and desizing operations as long as size recovery is not practiced. Generally, the caustic or bleach stream will degrade many size compounds to an extent that they cannot be recovered.
The jet weaving wastewater can be reused within the jet looms. Alternatively, it can be reused in the desizing or scouring process, provided that fabric impurities and oils are removed by in-line filters.
An automatic shut-off valve set to time, level, or temperature will control the flow of water into a process unit. One plant estimated that a reduction in water use of up to 20 percent could be achieved with thermally controlled shut-off valves.
A flow- or pressure-reduction valve can significantly reduce the quantity of water used in a wash or clean-up step. These valves are particularly useful in cleaning areas where operators are not always aware of the need for water conservation.
A program of maintenance, inspection, and evaluation of production practices should be established. Significant reductions in water use can be made by implementing the following:
- Minimizing leaks and spills,
- Maintaining production equipment properly,
- Identifying unnecessary washing of both fabric and equipment, and
- Training employees on the importance of water conservation.
The equipment used in a water conservation program is relatively inexpensive, consisting, in most cases, of valves, piping, small pumps, and tanks only. The operating costs for these systems are generally very low. Routine maintenance and, in some cases, electricity for the pumps, would be the major cost components.
For example, below are the costs for purchasing and installing the equipment necessary to reuse 75,000 gallons per day of bleach wastewater for scouring:
Pump $3,000 Tank/Sump $14,000 Piping $5,000 Electrical $1,000 Total cost $23,000 The yearly operating costs are estimated to be $1,300, which include the electrical power for the pumps and routine maintenance.
The payback period for a water conservation system will vary with the quantity of water saved, sewer fees, and costs for raw water and wastewater treatment. For example, the pay-back period for the system discussed above would be 3 months. After this initial period, the company would save over $95,000 per year in water, sewer, and energy costs.
In addition to these direct cost savings, a water conservation program can reduce the capital costs of any required end-of-pipe wastewater treatment system, which can cost several thousands of dollars per gallon of flow per minute. Thus, a substantial reduction in water flow can produce corresponding savings in treatment water costs. However, small or token reductions will yield very few, if any, savings.
- Bergenthal, J.F. Wastewater Recycle and Reuse Potential for Indirect Discharge Textile Finishing Mills: Volume 1-Technical Report. EPA-600/2-84-070a. U.S. Environmental Protection Agency.
- Ibid. Volume 2-Six Mill Engineering Reports. EPA-600-84-070b. Research Triangle Park, NC: U.S. Environmental Protection Agency. 1984.
- Environmental Pollution Control: Textile Processing Industry. EPA-625/7-78-002. Cincinnati, OH: U.S. Environmental Protection Agency. 1978.
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