The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the ...
Operator solves dairy issue for community & farmers
Above: Field service technicians continuously check quality levels at the dairy’s wastewater treatment while working around the clock.
The caller said he needed a wastewater operator on site as soon as possible. In addition, he needed the operator to work as long as one to three months, though the duration of the assignment was not important at the time; expediency was.
This is the kind of telephone call MPW Industrial Services receives on a regular basis because the company specializes in emergency response.
After placing a call to the dairy facility in the upper Midwest to learn more details, MPW understood the uncommon circumstances of the request and just how urgent the need was.
The dairy’s wastewater plant had fallen out of compliance, incurring hundreds of thousands of dollars in fines for discharges that exceeded the facility’s permit. As a result, the dairy had been forced to truck its wastewater to a treatment facility in another city for almost two weeks. This meant less wastewater could be processed, which, in turn, meant less milk could be processed into cheese.
Officials estimated the dairy, one of the largest employers in the community of more than 3,000 people, was operating only at about 20% to 25% capacity. Furthermore, farmers now had to ship their milk to a limited number of nearby competitor dairies, which depressed local prices.
Within 48 hours, MPW dispatched field service personnel to the dairy and had the wastewater plant operating within discharge limits. And within 72 hours, the wastewater plant was operating at full capacity, enabling the dairy to resume the receipt of nearly 200 tanker trucks of milk a day.
Officials estimate the dairy, one of the largest employers in the community of more than 3,000, was operating only at about 20% to 25% capacity.
Quickly understanding the wastewater plant’s operations was critical to restoring service, which requires the treatment of the proteins and fat lipids inherent in dairy effluent. In addition to having a high BOD, fat in the dairy effluent can stick to the walls of sedimentation tanks, creating issues when sedimentation rises to the surface.
Wastewater from the dairy’s processes also enters an equalization tank for pH adjustment. This is due to pH fluctuations that range from 2 to 12, depending on the quantities and strength of the sulfuric and citric acids, both of which are used to clean and rinse dairy process equipment.
Working with the chemical pretreatment supplier, MPW field technicians initially determined the optimal pH needed was between 6.2 and 7.5. However, as the technicians gathered more data while operating the wastewater plant, they discovered they could generate better results when the pH is adjusted between 6.8 and 8.3. If the wastewater contains large quantities of suspended solids, the wastewater enters a high-strength tank in lieu of the equalization tank.
Water from both tanks is then mixed with ferric chloride and a polymer, causing the solids to bind together. The dairy uses ferric chloride at the direction of municipal authorities. Previously, the dairy used aluminum sulfate in the treatment of its wastewater. However, this treatment created hydrogen sulfide—and its trademark foul odor—in the municipal sewer pipes. This scenario prevented workers from entering the treatment area and generated more than a few complaints from residents.
After chemical treatment, the wastewater is sent to the onsite dissolved air flotation (DAF) system, which removes suspended matter. DAF removes the solids by dissolving air in the wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank basin. The released air forms tiny bubbles that adhere to the suspended matter, causing the suspended matter to float to the surface of the water, which is skimmed off the top and transported offsite for use as cattle feed or fertilizer.
The remaining treated water, meanwhile, must meet certain requirements before it can be discharged to the municipal treatment plant. Field service technicians continuously check quality levels at the dairy’s wastewater treatment while working around the clock. Compliance requirements include COD levels below 2,000 mg/L, pH values between 6.5 and 10.5, and TSS levels below 450 mg/L.
Meeting municipal requirements is essential for several reasons. For example, the dairy’s wastewater constitutes nearly 50% of the volume treated daily by the municipal sewer authority. Any exceedance can impact the municipality’s permit issued by the state, which was the case when the dairy was out of compliance and necessitated the fines to the dairy.
Now that the dairy’s discharge is in compliance and the flow rate has been restored to an average of approximately 160 gpm during a 24-hour period, MPW is shifting its focus to training dairy employees to operate the wastewater plant.
Previously, dairy management asked its maintenance employees to manage the wastewater process but a lack of knowledge and competing priorities made this impractical. The dairy plans to hire new employees whose only responsibility will be the effective and efficient operation of the wastewater plant to avoid the conditions that prompted the urgent call to MPW for qualified wastewater operators.