BioCycle February 2011, Vol. 52, No. 2, p. 36
Golden Flake Snack Foods eliminated $100,000/month in sewer surcharges by installing an on-site treatment system.
BETWEEN 1998 and 2008, Golden Flake Snack Foods (Golden Flake) in Birmingham, Alabama saw its municipal wastewater surcharges rise from $800 to $1,000/month to $100,000/month – for the same daily discharged wastewater flow rate that ranges from 100,000 to 350,000 gallons. Jefferson County, where the 300,000 square-foot snack food processing plant is located, projected that the rate most likely would rise to $250,000/month within the next five years.
With close to 70 percent of its 250-plus work force living within a 13-mile radius of the plant, Golden Flake preferred to keep its 80-year-old headquarters and main manufacturing facility in Birmingham, and find a solution to reduce or eliminate the surcharges. The Alabama Department of Environmental Management, which sets standards for wastewater regulations within the state, made it clear that if Golden Flake could reach prescribed TSS (total suspended solids), BOD (biochemical oxygen demand), NH3-N (ammonia-nitrogen) and DO (dissolved oxygen) concentrations, it could receive a discharge permit to convey treated effluent directly into a creek that runs along the perimeter of its property, and bypass the Jefferson County sewer system altogether.
The plant manufactures and distributes a full line of snack food items, including potato chips, tortilla chips, puffed corn, corn chips, cheese puffs, cheese curls, onion rings and pork skins (its specialty). In 2009, the Birmingham facility processed more than 20 million pounds of snack foods totaling $120 million in sales, 95 percent of which was distributed within 12 southeastern states.
The production mix of potato chips, corn chips and pork skins can vary, causing the raw snack food wastewater to have varying strengths and consistencies. All of the plant’s wastewater handled through its on-site treatment facility comes mainly from the processing of potatoes and corn (no sanitary sewage enters this system). From their arrival on site, the potatoes are carried in a water flume to be peeled and sliced. The slices are then washed and put through deep fryers before being packaged. The flume and wash water is drained daily and discharged for onsite wastewater treatment.
Raw corn, for the production of corn and tortilla chips, is cooked in kettles with water and lime to loosen and remove the husks, then soaked in vats to increase the moisture content of the kernels. The kernels are then washed to remove impurities, milled, sheeted to run through ovens, deep-fried and packaged. Water from these processes is discharged after use for on-site wastewater treatment.
Pork skins arrive at the plant in pellet form and go straight into deep-frying, then seasoning and packaging. The majority of spent cooking oil is trapped in a pit and removed before entering wastewater treatment. The fryers are boiled-out weekly, contributing to the wastewater stream.
Raw snack food wastewater is pumped through vibrating screens that collect 15,000 to 20,000 lbs/week of large food particles. This organic matter is collected and transported to northern Alabama for use as animal feed.
MEMBRANE BIOREACTOR SOLUTION
From the time the facility was originally built in the 1950s, prescreened wastewater leaving the plant was received at a primary clarifier (for primary sludge settling) with supernatant discharged to the county sewer system (Golden Flake is permitted to release up to 400,000 gallons/day of wastewater). Stagnant wastewater in the primary clarifier was not aerated or covered and would produce odors. The clarifier was located along the edge of a street, where subsequently a housing development had been built, and the odor was becoming an issue with residents.
“The wastewater being decanted to the county sewer system had BOD and TSS concentration levels in the thousands, exceeding maximum surcharge levels,” says David Jones, Executive Vice President of Operations for Golden Flake. “As our surcharges continued to escalate, we began looking for a treatment technology that could not only handle our high-volume peak flows of 350,000 gpd, but also produce an effluent that was below the Alabama Department of Environmental Management’s maximum allowable discharge concentration limits for BOD, TSS, NH3-N and DO.” Because the site is landlocked with no room for expansion, a conventional activated-sludge facility with the footprint requirements for spray fields to process the wastewater flow was not an option.
Golden Flake worked with ADI Systems to install a membrane bioreactor (MBR) system to treat the raw waste-water following the vibrating screens. The process, based on technology developed by ADI Systems and Kubota Corporation, is a form of activated sludge technology that uses a submerged membrane barrier for the liquids/solids separation and reactor biomass retention functions. The system can fit on compact sites. Treated effluent could then be discharged into the Upper Valley Creek, eliminating wastewater being discharged to the county sewer system.
After a successful test using a 350-gallon MBR pilot plant on-site at Golden Flake to treat a small stream of Golden Flake’s prescreened wastewater, a full-scale ADI-MBR system was installed in February 2009 and began operating six months later. It consists of a pre aeration tank and two membrane basins, each equipped with double-decker submerged membrane units (SMU), along with aeration blowers, a re-aeration chamber, pumps, instrumentation and controls. Treated effluent is passed through the membranes via a slight suction, and then aerated to meet the dissolved oxygen limit prior to discharge to the adjacent stream. Waste activated sludge is dewatered on-site with a screw press and the sludge cake is land applied on farms. About 20 tons/week of dewatered sludge cake are generated.
The system has a design hydraulic retention time of approximately one day, and is designed to treat a daily influent flow rate of up to 400,000 gpd. The system treats prescreened wastewater with BOD and TSS concentrations that range from 1,000 to 10,000 mg/L and 200 to 12,000 mg/L, respectively. It produces effluent that is lower than the discharge limits set by ADEM: 6 ppm DO (>6 ppm DO limit). Up to 250 gallons per minute of effluent is released into Upper Valley Creek, which helps improve oxygenation of the water flow within the small watercourse.
Expected payback of the system is three to five years. In addition, says Jones, the treatment system is fully automated: “Our maintenance supervisor can control the whole system, including every pump and motor, from one location in the plant or from his home on his laptop. This provides a control flexibility we did not have before.”
Jim McMahon writes on water and wastewater systems.
February 22, 2011 | General
Snack Food Manufacturer Reduces Wastewater Surcharges
BioCycle February 2011, Vol. 52, No. 2, p. 36