Application Review:
Industrial Wastewater Recycle and Reuse Process Handles Various Waste Streams and Exceeds Environmental Goals

CHALLENGE

A machine tool manufacturer was challenged with changing their wastewater management processes to mitigate increasing water use and to virtually eliminate the need for disposal of hazardous waste.

PRODUCTS UTILIZED

Ultrafiltration

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Industrial wastewater comes in many forms. Typically the water waste streams are generated from metalworking processes, parts finishing, parts washing, and plant cleaning. Each of these areas use varying amounts of water and requires careful clean-up and discharge to meet safety, environmental, and municipal regulations and requirements. Water as part of metalworking processes can be challenging to clean due to the range of containments; from particulate and fines, to suspended solids, emulsified oils, to harmful chemical compounds and surfactants, high-concentration organic elements and compounds.

Wastewater treatment in the metalworking industry is typically implemented for cost reduction, plant safety, environmental compliance, and risk mitigation avoiding financial penalties and liability. As metalworking companies evaluate their wastewater treatment goals against a return on investment objective; the two are not always aligned. Todays’ broad-spectrum of industrial wastewater treatment technologies have changed this dilemma however; now achieving goals and meeting reasonable ROI expectations are feasible with tailored wastewater treatment systems.

Following is a working example of how a tailored Ultrafiltration System can support the wastewater treatment needs of both a deburring process wastewater and mop water in the same wastewater treatment system.

The Need for Comprehensive Wastewater Treatment – Recycle and Reuse Process

A machine tool manufacturer was challenged with changing their wastewater management processes to mitigate increasing water use and to virtually eliminate the need for disposal of hazardous waste. Above a certain threshold of hazardous waste generation, the EPA enforces more stringent regulation requirements and larger potential fines. At current generating levels, the tool manufacturer needed to meet or exceed

By implementing a new wastewater recycle and reuse process, the company would maintain a small waste producer status while saving an estimated 300 gallons of water usage per day.

Determining the Best Technology for the Application

Best practices for solving wastewater filtration challenges starts with understanding the current state of the wastewater make-up. This is accomplished through water testing analysis. The testing provides important data of the make-up and pH of the wastewater; it is the starting point from which engineers will work to determine the right system for meeting required cleanliness standards. This process involved sending samples of mop water and tumbling water to PRAB for analysis.

Engineering a single wastewater treatment system to handle both mop water and vibratory waste streams is not typical. However, cost justification for a stand-alone system for the mop water was not feasible. Without recycling of the mop water the company would not achieve its zero waste targets; therefore, a system had to be designed to handle all waste sources.

The water analysis for each waste stream is shown in Figure 1, each containing varying levels of suspended solids, Chromium, and Lead. The mop water also contained emulsified oils while the vibratory water had measurable levels of Zinc. The water analysis, coupled with the goals of reuse and meeting EPA requirements determined the need for an Ultrafiltration unit.

While the Ultrafiltration (UF) unit would be the heart of the wastewater treatment process, making the system viable for all waste streams and for the removal of suspended solids, a complete engineered wastewater treatment system was deemed the best option for the application.

Engineered Wastewater Treatment Systems Meet Recycle and Reuse Goals

The engineered wastewater treatment system starts with a 500 gallon cone bottom holding tank and high/low level sensors, (Figure 2, 1) a sump pump supplies the wastewater from the deburring stations to the holding tank. The high level sensor inside the tank triggers a double diaphragm air pump to start. This pump pulls the vibratory wastewater from the tank and feeds it to a Paperbed filter (2). The pump runs until the low level sensor is reached, thus allowing the bulk of the solids to settle into the bottom of the tank for later disposal. The cone shaped bottom of the holding tank provides for easy collection and removal of the sludge.

PRAB Wastewater Sample Analysis Chart

The Paperbed filter is equipped with an integral magnetic separator. These components work together to attract and filter larger ferrous particulate down to 50 micron and smaller non-ferrous fines down to 25 micron. The filtered liquid also passes through a Size 2 bag filter with 200 micron filtration for the capture of finer particulate (3). The next step in the process moves the wastewater into a 300 gallon cone bottom process tank that feeds the Ultrafiltration membranes. At this point in the treatment process the wastewater contains approximately 54.9 mg/L insoluble Cr (Chromium) and .15 mg/insoluble Pb (Lead) the liquid makes a single pass through the Ultrafiltration membranes to achieve clean water standards for reuse in the facility (4). After the pass through the UF the tested and documented Cr levels are .13 mg/L and Pb levels are

The permeate is gravity fed to a customer supplied clean holding tank and transferred on demand to the vibratory deburring machines (5). To maintain consistent water flow and proper levels for the vibratory deburring machines and to prevent the possibility of stagnant water, the UF filtration system is designed to have a continuous feedback loop. The feedback loop includes the permeate in the vibratory holding tank as well as the CIP tank. Both tanks are equipped with high level sensors that allow water overflow to be fed into the main process water tank and run back through the UF (6).

Revolutionary Wastewater System Design Handles Two Different Waste Streams

The engineered wastewater treatment system was also required to handle the wastewater stream from mop water. The challenge to making this system work effectively means handling the cleaners and free paraffins present in the mop water and running it through an Ultrafiltration system so the membranes are not damaged. The system must also eliminate the possibility of cleaners creating foaming in the vibratory deburring bath. The engineered wastewater treatment system is designed with a series of diverting and by-pass valves to allow the mop water to also filter through the Ultrafiltration system. Mop water enters the system at the inlet of the double diaphragm pump downstream of the dirty holding tank (1a). The water is pumped into the Size 2, 200 micron bag filter and then into the 300 gallon process tank (2a). This wastewater is pumped into the Ultrafiltration unit and then gravity feeds into a Customer Supplied Clean Mop Water holding tank (3a).

After each mop water cycle the system is flushed with caustic cleaner to remove any solvents cleaning solutions prior to running the process wastewater again.

PRAB Engineered Ultrafiltration System Illustration

Comprehensive Wastewater Filtration Improves Operating Efficiencies and Cuts Costs

The complete engineered Ultrafiltration Wastewater Treatment System has been operating since November 2014. The system has proved effective at slashing new water costs and dramatically cutting the expense of waste hauling and water recovery. In addition, the system has improved the operating efficiency of the deburring operation by maintaining a consistent, clean water source for vibratory operations. The ultrafiltration system has reduced Chromium levels in the wastewater from 40PPM to 0.05 PPM (EPA requires < 5 PPM) and the system is estimated to have a total return on investment of 1.5 years.

The system is the first step for this industrial Swiss Tool manufacturer to be better prepared for future changes to production, EPA standards, and a ever changing industrial market that requires complying to world class standards.