NJTAP Pollution Prevention Case Study -- Precise Products

Industry: Hardware Manufacturing

Background

Precise Products is a small company that manufactures spring pins in Paramus, New Jersey. The pins are cylindrical metal tubes which are used as industrial fasteners. To reduce the regulatory burden at the facility the plant manager hoped to recycle his process water, which could eliminate the company’s wastewater discharge to the sewer system.

During manufacture, spring pins are cut and slit, which can leave rough edges. In order to smooth these edges, the pins are placed in tumbling barrels and treated with detergents, abrasives, and surface passivants. This also imparts a corrosion-resistant surface to the pins.

Each barrel holds approximately 50,000 pieces. Chemicals and abrasives are added to the barrels manually and fluidized with five to ten gallons of tap water per load. After piece-variable tumbling, each barrel is drained and tumbled dry. The wastewater from the tumbling barrels contains residual cutting oils, spent chemicals, abrasives, and metal shards.

Eliminating Wastewater Discharge

Previously, wastewater passed from the tumbling barrels, then flowed through a series of three settling tanks. Residual oils floated to the surface of each tank, while suspended solids settled to the bottom. The grossly clarified wastewater was then pumped to a 500 gallon holding tank, which was emptied into the sewer weekly. Oil float from each settling tank was collected daily by synthetic absorption pads. Bottom solids were drummed off for appropriate solid waste disposal.

Wastewater was released into the local sewer system, requiring an annual discharge permit. As a condition of the permit, Precise Products had its wastewater tested monthly, costing the company over $5,000 per year.

Test data showed that the existing wastewater pretreatment performed well and that minimal amounts of the deburring compounds were surviving the process attrition in the tumbling barrels. These results indicated that it would probably be possible to recapture the pretreated wastewater and redirect it back to the barrels, instead of discharging it to the sewer.

Oil Removal Options

In order to recapture and reuse the wastewater, the amount of oil in the water had to be controlled. The company studied several oil removal options and determined that skimming was the most applicable and cost-effective option. The existing three-tank settling system could provide the necessary mechanism in which to separate bottom solids from surface oil and grease flotation.

Since the existing pad skimmers performed well (and because alternative methods of skimming would cost more to install and operate), Precise Products opted to retain the existing wastewater equipment. It was still necessary to develop a method to reclaim and reuse the treated wastewater.

Wastewater Pretreatment Modification

In order to use the pretreated wastewater to recharge the tumbling barrels, Precise Products would have to reroute the wastewater back to the tumbling barrels.

The company decided to redesign the existing wastewater holding tank to function as an unattended, hydraulically-safe component. Modifications to the existing wastewater holding tank consisted of the following additions:

• high-level and low-level alarms;
• a tap water supplemental connection to compensate for water losses from sludge removal and drag-out; and
• a flooded suction recycling pump and hose line to the tumbling barrels.

The New System

In Precise Products’ new treatment process, water from the tumbling process flows through three settling tanks. Oil is skimmed from the tops of the tanks, and solids are removed from the bottoms. They are disposed of off site. The clarified wastewater is pumped to a 500 gallon holding tank, where small amounts of makeup water are added. From there, it is pumped back to the tumbling barrels to be reused. A switch at the barrels allows the operator to activate the system. No wastewater is pumped to the sewer.

There has been no reduction in the effectiveness of the cleaning and surface preparation of the spring pins. In fact, the quality of finish has improved slightly. This may be because the fine abrasive particles in the recycled water polish the work surfaces to a higher degree.

Environmental Effects

With the new recycling system, Precise Products has significantly reduced the amount of municipal water it uses. Although it still generates sludge and oil absorption pads in the same amounts as previously, the company no longer discharges industrial wastewater to the local sewer system and consequently no longer needs a discharge permit.

Cost Savings

Table 1 shows the cost of operating the original wastewater system, and compares them to the cost of operating the new system.

By using existing equipment, Precise Products was able to reduce both its operating costs and its environmental impacts. As the table shows, the biggest savings come from not having to pay for monthly wastewater laboratory analysis, which previously was required by the company's wastewater discharge permit.

As a result of the wastewater recycling project, the company saves over $5,000 per year. The payback period for the project was six months. Additional savings, not quantified, include the improved surface preparation of parts and the saved manhours since permit preparation is no longer necessary.

Conclusion

The Precise Products case demonstrates how a company can use pollution prevention to save money while benefiting the environment. By making simple changes to recycle its treated wastewater for process reuse, the company was able to significantly reduce its water use, and eliminate wastewater discharge into the sewer system, while saving over $5,000 a year.