Office of Technical Assistance Executive Office of Environmental Affairs Commonwealth of Massachusetts

Summary

Standard Uniform wanted an efficient, cost-effective replacement for the sulfuric acid used to adjust the pH of its wastewater to the levels required in its discharge permit. The company, working with OTA, identified an easy to install carbon dioxide system that achieves the required results for about the same dollar cost as the sulfuric acid and eliminated its TURA filing requirement for H₂SO₄. The new system also eliminates odor problems from hydrogen sulfide emissions and is much safer and healthier for the company's employees and for the environment.

Background

Standard Uniform Services, in Agawam, Massachusetts, rents and maintains industrial uniforms, wiping cloths, walk-off mats and other related textile products for auto service centers, machine shops, printers, service companies and many other industrial and commercial customers in western Massachusetts and Connecticut. Standard employs 50 associates and, in addition, 12 workers from Aditus, a job placement agency for workers with disabilities. The company washes or dry cleans and repairs 50,000 pounds of textiles for 1,100 customers each week. When the company, a division of Standard Management of Norwood, Massachusetts, moved into its new facility in the Agawam Regional Industrial Park in late 1990, a new wastewater pretreatment system was installed to meet local wastewater compliance standards for pH and fats, oils and greases (FOG). Shortly after moving into the new facility, General Manager Mark Haymes met OTA representatives at a dry-cleaning trade seminar and began what became a joint effort to find alternative cleaning processes that would use safer and/or reduced levels of chemicals. The washing operation is now nearly toxic free; a project to reduce the amount of perchloroethylene (PER) used for dry cleaning is underway and making progress.

Toxics Use Reduction Planning

Standard wanted to incorporate systems and processes in its new facility that would provide the greatest personal safety for employees and have the least environmental impact. The company added a metered acid injection system, which pumped more than 12,000 pounds of acid per year into the pipe carrying water to Standard's unique wastewater treatment system. The acid lowers the pH of the highly alkaline 25,000 gallons of wastewater a day that enter the specially designed large, open wastewater treatment tank. Sulfuric acid was recommended as strong enough to quickly achieve the required level of pH adjustment at an acceptable cost, but the strong acid is corrosive to the equipment and produces unpleasant hydrogen sulfide odors. The acid also helps remove some of the emulsified grease and oil from the wastewater.

OTA and Standard worked independently to develop a system that would be safer than the acid and as readily available, simple, and trouble free, while continuing to be chemically and cost effective. OTA found that citric acid could be used with no modifications to the existing system and would meet all of the criteria except cost, which was at least 10 times as much as the H₂SO₄. Standard sought recommendations from its detergent, chemical and equipment vendors and from the Institute of Industrial Launderers, the national trade association. Most of the recommendations were for other acids, but one vendor reported that another industrial laundry was successfully using CO2. The other laundry confirmed that CO2 effectively reduced pH to levels acceptable to most publicly owned treatment works (POTWs), but that it had never used any other system and was unable to offer any comparative data. Standard asked CO2 suppliers for cost and supply information and installation proposals. The responses convinced Standard to do a pilot test. OTA helped to develop the process for using the alternative pH adjustment system.

Toxics Use Reduction Modifications

Standard added a gas diffuser and control valve to inject CO2 into the line that brings wastewater to the treatment tank. Some additional piping and a CO2 supply were also needed. One of Standard's customers, in the industrial gas business, supplies the CO2 in 378 pound portable, refillable containers. The diffuser and valve cost, respectively, $400 and $125; the piping was another $120 and about 25 hours each were required for research and installation/modification. Maintenance and wastewater operators helped to design, install and modify the treatment system and they have been trained to monitor and control flow rates to achieve the required pH adjustment.

Results

Reductions Achieved: Within one week, Standard personnel could adjust the CO2 flow rate without metering equipment to maintain the pH of the wastewater at the levels required by the discharge permit. A five-gallon pail of H₂SO₄ will be kept available for what is expected to be rare emergencies. The changes Standard has made resulted in more than a 99% reduction in the use of the chemical and is far below the level that has to be reported in annual TURA reports. There are no toxic byproducts from the process and there is no H₂S causing noxious odors or requiring tests.

Economics: The cost to install the CO2 system was less than $650. Carbon dioxide is used at a weight ratio of 1.8 pounds for each pound of sulfuric acid previously used to achieve the required pH adjustment and the cost will be about $4,500 per year compared to about $1,400 for sulfuric acid, but the higher purchasing costs will be offset by savings in other areas. The savings on TURA filing will be about $2,950 per year. Corrosive damage to equipment should be substantially reduced; the expected life of the $50,000 steel tanks is now ten instead of five years. Improvement in the health and safety of the work environment also has the potential to lead to substantial savings.