Sep 1, 2010 12:00 PM
Wastewater handling becoming more costly for food wash racks
Wastewater disposal is becoming increasingly complex for wash racks that clean foodgrade products. Facilities face stricter discharge limits, higher fees, and much more scrutiny by local and state regulators.
The growing challenges were highlighted during a panel discussion at the National Tank Truck Carriers 2010 Tank Cleaning & Environmental Council Seminar in Nashville, Tennessee. Panel participants included Brad Young, Lafayette Sani-Wash.
Some foodgrade wash racks are seeing wastewater treatment fees as high as $10,000 a month. These higher fees can completely erase a wash rack's profits, and it could become a business survival issue for many smaller facilities.
Officials at publicly owned treatment works (POTWs) say they are being pressured by state and federal regulators to strengthen wastewater discharge requirements. POTW officials also contend that their facilities were designed primarily to treat residential wastewater with a biological oxygen demand (BOD) of approximately 250. Most foodgrade tank wash racks produce wastewater with a much higher BOD count.
For some foodgrade wash rack operators, the solution has been to find alternative disposal options for the wastewater. Many are shipping heels and wastewater away for agricultural uses, such as animal feed. Some are exploring options for sending foodgrade wastewater to ethanol plants in the future.
Lafayette Sani-Wash took a different approach, according to Young. Oils and concentrated waste solids are hauled away for disposal, but the commercial wash rack pretreats a majority of its wastewater in-house.
Located in Lafayette, Indiana, the three-bay wash rack cleans sweeteners, vegetable oils, starch, flours, chocolates, fruit juices, and milk. Every day, the facility uses about 20,000 gallons of water to clean 50 to 70 tank trailers. It has been doing that for more than 20 years.
“The city of Lafayette has monitored the wastewater we discharge into the city sewer throughout that time,” Young said. “They come in for a week once every quarter. Our limits typically were around 1,000 for BOD and suspended solids, but we usually ran around 6,000 on both.
“Even though we were over our limits, we would just receive a letter from the city telling us our readings with no mention of fines or surcharges. However, about two years ago, the state of Indiana notified the city that the policy needed to change. Now we have a set limit of 250 for BOD and solids. As long as we stay below 250, there is no problem. Surcharges are applied for levels between 250 and 1,000, and the fees can run $500 to $1,000 a month.
“If we go over 1,000 for BOD or solids levels, we're in violation of our permit, and the POTW starts sending official warning letters. Eventually, they could shut off our water. Our only choices were to haul away up to 20,000 gallons of wastewater daily or build some sort of treatment system to get down under 250. We decided it made more sense to stay on the city wastewater treatment system than to haul everything away.”
With suggestions and advice from the local POTW staff, the Lafayette Sani-Wash team designed and built its own aerobic microbiological wastewater treatment system. The system can treat 15,000 to 20,000 gallons of wastewater a day.
“It took us a lot of trial and error, but we've had the system up and running for two years now,” Young said. “We haven't faced any fines or surcharges during that time. “This is a home-made system, and there is no guarantee that it would work in other wash rack operations, but it is performing well for us.”
One reason for the success of the system is that Lafayette Sani-Wash maintains tight control over the wastewater stream. Sweeteners are a challenge for the micro organisms that consume the biological wastes, so heels and first rinse water from sweetener trailers is collected and sent to local hog farmers.
“BOD levels are so high in sweetener wastewater that the bugs can't handle much of it,” Young said. “Foodgrade heels are a problem in general, because the bugs don't like too much of anything.”
Pre-wash rinse water goes to two underground pits that are used to separate oils and settle starch, flour, and other solids. Oil is skimmed off daily and hauled away for use in animal feed and the sludge at the bottom of the pits is sucked out monthly and hauled away for disposal.
Wastewater from the first two pits is pumped to a third pit and then to a dissolved air flotation tank that is used as an above-ground separation pit. Any residual oil from the first two tanks floats to the top, and any remaining solids sink to the bottom.
“This really cleans up our wastewater before we begin feeding it to our biological treatment system,” Young said. “Hopefully, all of the suspended solids are out of the water by this point, but we still have lots of dissolved solids. We pump this water into a 25,000-gallon rail tankcar that we use as an equalization tank and to hold extra wastewater during busy times. We have to make sure we have plenty of food for the bugs.”
Microbiological treatment occurs in two 10,000-gallon vertical aeration tanks, each with air bubblers on the bottom. The tanks are insulated to protect the microbes during cold weather. Microbes for the system were obtained from other wastewater treatment plants. Wash rack workers closely monitor the treatment system to ensure that the microbes remain in good health.
“We went with 20-ft-tall vertical tanks because oxygen bubbles have more time to dissolve into the water,” Young said. “The bugs can't live without the dissolved oxygen, and the more they eat, the more oxygen they need.”
Treated wastewater goes through a clarifier before being released into the city sewer. Solids with microbes attached settle to the bottom and are pumped back to the aeration tanks. “We don't want to lose those bugs,” Young said.
Treatment operations are monitored constantly to keep the pH level between six and nine, which is where the microbes like it. Young stresses the importance of keeping everything in balance with the microbiological system. “You don't want too much of anything,” he said.
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