Dairy processor cuts wastewater treatment costs with energy efficient blower technology

It would be hard to list items more likely to be found in an American home than milk. And since it’s steadily consumed, the supply of milk is continually replenished. Raw milk from dairy farms is delivered 365 days a year to dairy processors across the country, including Garelick Farms. The company’s Franklin, Massachusetts facility, situated on the original Garelick Homestead established in 1931, processes fluid milk for sale in plastic gallon and half gallon bottles sold primarily in grocery stores. “In Franklin, about 90% of our volume is gallons, 10% half gallons and other products,” according to Rink Wheeler, Engineering Manager for Garelick Farms. “We strictly make drinks: 1%, 2%, skim and whole milk, orange juice and others. Up to 50 tankers of raw milk arrive every day of the year and we produce two million gallons of milk each week.” Some processes involved in making dairy products create wastewater, which Garelick Farms cleans up in its onsite treatment facility. The wastewater treatment process involves two main steps. The first takes place in a 4,500,000 gallon bulk volume fermenter tank. A membrane at the bottom separates milk fats, milk solids and organic solids from liquid so the solids can be digested by anaerobic bacteria. The secondary treatment process takes place in a re-aeration tank where very small air bubbles are injected into the water by aerators on the bottom of the tank. These fine bubbles efficiently transfer oxygen to the water, assisting aerobic bacteria in producing enzymes that further break down waste. Fine bubble aeration is the most sustainable, energy efficient approach to wastewater aeration. The steady stream of air required for the aeration system is produced by a low pressure air compressor known as a blower. The largest operating cost component for the aeration process is power to run the blower. Companies that operate a wastewater Treatment process are increasingly recognizing the value of replacing less efficient positive displacement rotary lobe blowers and upgrading to high efficiency blowers that employ rotary screw technology. “For years we had been supplying air for re-aeration with several positive displacement blowers,” according to Wheeler. “But when we started a project to replace the tank membranes, we realized the increased membrane capacity would require a higher volume of compressed air to operate. Initially we were looking to add more lobe blowers, but I wanted to learn about other options. I asked Rick Brown, who has a lot of experience working with projects involving compressed air, to give us some advice.”

Rick Brown is the Senior Sales Engineer with IMEC, a longstanding Atlas Copco business partner located in nearby Ayer MA. IMEC is a custom mechanical design/build firm with unique compressed air experience and also a certified Project Expediter (PEX) of the local electric utility, National Grid. Brown recalls that Garelick Farms had been using three (3) 25-horse-power positive displacement lobe-type blowers, each with 250 CFM flow capacity for a total of 750 CFM. “With two new membranes going in, Rink Wheeler was looking to double CFM capacity to 1500,” Brown says. “The simple option was to get an additional positive displacement blower. Another approach would be a single, larger positive displacement blower to satisfy the entire demand. A 125-horsepower unit that could satisfy the demand was quoted, but the noise level was already scary with the existing blowers creating around 100 dB(A) each. If Garelick Farms stayed with positive displacement technology, they’d be making the work environment even louder and operating inefficiently. I thought we could do better.” At this point, Rick Brown consulted with Ron Whelan, the local Atlas Copco Oil-free Air and Key Account Sales Manager, and the two combined efforts to select a rotary screw blower solution for the project. “The variation in effluent output from the Garelick Farms wastewater treatment plant and resultant compressed air requirement at different load points made Variable Speed Drive a natural fit for the application,” Whelan explained. An Atlas Copco model ZS 75+VSD was selected to meet both the flow and pressure requirements. Brown reached out to National Grid, which offers financial incentives to companies that install energy conserving equipment, to learn whether Garelick Farms could benefit. “I prepared a comparison of product data to determine if the project qualified under the National Grid New Construction Custom program,” Brown explains. “To qualify, you specify a base case solution, with equipment that is less expensive to purchase but also less efficient to operate, and a proposed case solution with equipment that requires a larger initial investment but operates with higher energy efficiency. Our base case was a new positive displacement rotary lobe blower sized for the application. Our proposed case included an Atlas Copco ZS 75+VSD oil-free rotary screw blower with Variable Speed Drive, which provided energy savings to establish the incentive. We used the positive displacement blower curve and Atlas Copco’s engineering data for our screw blower to calculate those savings based on the varying load requirement at Garelick.” The energy calculations determined that operation of the ZS 75+VSD would result in annual energy savings of 83,647 kWh compared to the equivalently sized rotary lobe unit. National Grid offered Garelick Farms an incentive of $17,271 to invest in the more energy efficient Atlas Copco equipment, resulting in simple payback period of just 18 months. “There was no question this was the way to go,” says Wheeler, “but a key issue was that our management decided they wanted the new blower right away. We had already scheduled the membrane replacement, which involves pumping down the 600,000 gallon water treatment system, and they didn’t want to do it twice. It takes several weeks to build and deliver a brand new ZS 75+VSD blower, but Ron Whelan and the Atlas Copco team were able to source a similarly sized new machine for us to use on loan until our blower was built. Actually they went through hoops to secure that blower for us. As it turned out, the loaner had virtually the same specifications as what we ordered and it was meeting our demand just fine in operation. Given that the time and effort involved in replacing the loaner with another machine that was practically identical, we arranged it with Atlas Copco so we could maintain possession of the loaner.” Whelan says, “I was ecstatic that our team was able to react quickly and pull something out of stock to help the customer. Garelick Farms was able to not only satisfy their tight project timeline, but also could start realizing the energy saving benefits sooner.”

A requirement of the National Grid incentive was installation of a kilowatt meter to record the actual power consumption after the new blower was installed and operating. “It turns out our projections were too conservative,” Brown recalls. “We saved roughly three times the amount of power we initially forecasted, largely due to the superior turn-down capacity of the ZS 75+VSD screw blower when compared to positive displacement blowers that can only run flat out. The realized savings projection increased to $22,000 a year, which shortened the projected payback period by several months. The initial purchase cost was higher than the positive displacement lobe blower, but the it’s so much more energy efficient in operation, particularly in an operation that runs 24/7, that the savings paid back the additional investment in just over a year.” At Garelick Farms, the screw blower’s speed varies according to the wastewater’s dissolved oxygen (DO) level, which moves up or down within a range based on both pure volume and effluent composition. A sensor in the aeration tank reads instantaneous DO level and converts the value to blower speed. If DO drops below the low end of the operating range, more oxygen is required and the sensor sends a signal to the blower to increase speed until DO level returns to normal. If the DO level is too high, less oxygen is required and the sensor sends a signal to slow down the blower. “It works, slicker than a trout,” says Wheeler. “On the display I can see nice trend lines with the speed of the blower going up and down in sync with the level of DO. All the while, pressure remains relatively constant, between 12 and 14 PSI. The previous system did not have any automation and only two run options: full speed and off.” The electrical energy consumption also trends on the same path as DO levels at the site. An additional benefit of the upgrade to the ZSVSD screw blower is the sound level in the utility room has been reduced to 72 dB(A) and hearing protection is no longer required. “You can have a conversation standing right by the unit, it’s so quiet,” says Wheeler. “It’s what I call an outstanding non-electric benefit. I can tell you that our equipment operator is much happier. Since we’re saving money too, everyone’s happier.” Wheeler adds that the wastewater treatment process gives off methane, but rather than simply venting the methane to the atmosphere, Garelick plans to capture and reuse it. A system of five micro turbines to generate power from captured methane is about 90% complete and the Franklin plant has received capital commitments to get the system fully operational during 2014. Rink Wheeler credits both Rick Brown of IMEC and Ron Whelan of Atlas Copco for guiding the Garelick Farms wastewater project from concept to reality. “How you position and execute a project proposal can have a considerable impact on the financial result,” Brown says. “What we do at IMEC is provide a turnkey installation service and facilitate and manage the rebate process so the customer maximizes the return on their project. We consider ourselves to be partners with the equipment buyer, National Grid and Atlas Copco. We’re all working together to help our customers operate a more productive process with lower total cost and reduced environmental impact.”