Membrane Bioreactor Helps Eliminate Municipal Surcharges
Golden Flake Snack Foods, located in Birmingham, AL, was faced with a tough decision, either come up with a solution to stem the escalating municipal wastewater surcharges it was being assessed, or move its 300,000-square-foot snack food processing plant out of the county to stem the significantly rising costs.
BY JIM MCMAHON
Golden Flake Snack Foods, located in Birmingham, AL, was faced with a tough decision, either come up with a solution to stem the escalating municipal wastewater surcharges it was being assessed, or move its 300,000-square-foot snack food processing plant out of the county to stem the significantly rising costs. In 1998, the plant was paying $800 to $1,000 per month to Jefferson County in surcharges for decanting its 100,000 to 350,000 gallons of wastewater into the county's municipal sewer system. By 2008 that figure had escalated to $100,000 per month in surcharges for the same daily discharged wastewater flow rate, with county projections that the rate would most likely rise to $250,000 per month within the next five years.
Given the fact that 68 percent of Golden Flake's 250-plus work force lives within a 13-mile radius of the plant, the company preferred to keep it 80-year-old headquarters and main manufacturing facility in Birmingham, and find a solution to reduce or eliminate the surcharges. This meant, in essence, getting off of the county sewer system.
|Membrane tanks covered with removable aluminum panels to reduce leaves and other debris from entering the tanks.|
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 Golden Flake 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. Port skins are its specialty. The company produces over a dozen varieties and sells more pork skins in the southeastern United States than any other company.
In 2009, Golden Flake's 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 plant's production mix of potato chips, corn chips and pork skins can vary, causing the raw snack food wastewater to have varying strengths and consistencies, with flow rates ranging from 100,000 to 350,000 gallons per day.
All the water treated at the on-site wastewater treatment facility comes from the production of snack foods (no sanitary sewage enters this system), mainly from the processing of potatoes and corn.
Raw snack food wastewater is pumped through vibrating screens which collect 15,000 to 20,000 pounds per week of large food particles. This organic matter is transported upstate to be used as animal feed.
From the time the facility was originally built in the 1950s, the pre-screened 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 of wastewater per day). The stagnant wastewater in the primary clarifier was not aerated or covered and would produce off-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.
|Aeration of activated sludge in one of Golden Flake's membrane tanks during operation of the ADI-MBR system.|
"The wastewater being decanted to the county sewer system had BOD and TSS concentration levels in the thousands, exceeding maximum surcharge levels" said 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."
Engineering a Solution
Golden Flake brought in ADI Systems to engineer a solution. The problem was somewhat complicated by the fact that the plant is landlocked in its position, being in the Birmingham inner city. There was no room for site expansion, and little available room for a conventional activated-sludge facility.
ADI Systems recommended the implementation of a membrane bioreactor (MBR). The ADI-MBR process, based on technology developed by ADI Systems and Kubota Corp., is a form of activated sludge technology that uses a submerged membrane barrier to perform the liquids/solids separation and reactor biomass retention functions, instead of gravity clarification, which eliminated problems associated with sludge settling and separation.
ADI Systems commissioned a 350-gallon MBR pilot plant onsite at Golden Flake using a small stream of pre-screened wastewater. The pilot plant operated for three months and successfully demonstrated that the technology was easy to operate, could consistently meet the effluent limits, and produce a direct discharge quality effluent while being situated on a site with a compact footprint.
"The technology is really what sold us," Jones said. "We toured a couple MBR facilities in Georgia that were using the Kubota submerged-membrane technology, and we were very impressed by what we saw."
The MBR system provides a near-absolute barrier to suspended solids and allows for operation at higher mixed liquor suspended solids (MLSS) concentrations (typically 10,000 to 18,000 mg/L versus 2,000-5,000 mg/L as in conventional activated sludge systems) resulting in longer solids retention times, less waste sludge production and a much smaller footprint.
The Golden Flake system consists of a pre-aeration tank and two membrane basins, each equipped with double-decker submerged membrane units. The system includes aeration blowers, a re-aeration chamber, pumps, instrumentation and controls. The total package includes a control building with a dewatering press/conveyor system, automatic composite samples, laboratory, office and PLC systems.
During system operation, treated effluent is passed through the membranes via a slight suction, and then aerated to meet the DO limit prior to discharge to the adjacent stream. Waste activated sludge is dewatered onsite with a screw press and the sludge cake is removed for disposal.
"Membrane treatment technologies are often employed when higher quality effluents are required," said Mike McDermaid, Project Manager for ADI Systems. "Additionally, the ADI-MBR system is ideal when available plant footprint is very limited, and when the wastewater characteristics make conventional gravity settling technologies difficult or ineffective."
The system at Golden Flake provides a design hydraulic retention time of approximately one day, and is designed for a daily influent flow rate of up to 400,000 gpd. The system treats pre-screened wastewater with BOD and TSS concentrations that range from 1000 to 10,000 mg/L and 200 to 12,000 mg/L, respectively.
Construction began on the new system in February 2009. It became operational in August 2009, and consistently produces effluent that is lower than effluent discharge limits set by the Alabama Department of Environmental Management: <2ppm TSS, (<30 ppm TSS limit); <5 ppm BOD, (<10ppm BOD limit); <1 ppm NH3-N (<1.5 ppm NH3-N limit); and >6 ppm DO (>6ppm DO limit).
Up to 250 gpm of clean, high-quality effluent is released into Upper Valley Creek, and serves to enhance the downstream riparian environment by improving the oxygenation of the water flow within the small watercourse.
The final effluent produced by the ADI-MBR system is clean enough to reuse for certain applications, such as site irrigation. The waste activated sludge from the system is pumped through an on-site dewatering press to reduce the overall sludge volume to 20,000 pounds per week, which is then trucked upstate for farm fertilization.
The entire treatment system is automated, Jones said.
"Our maintenance supervisor can completely control the whole system from one location in the plant or from his home on a laptop. Every pump and motor can be controlled from the computer screen. This provides a control flexibility we did not have before," he said.
|ADI-MBR system at Golden Flake, showing the preaeration tank (right), pre-cast concentrate membrane tanks and aeration blowers (center), and operations building (left). The operations building houses the electrical systems, PLCs, sludge dewatering system, pumping systems, laboratory and office.|
One of the biggest benefits of the system is that Golden Flake is no longer discharging primary treated wastewater into the county sewer system, and is no longer paying escalating surcharges for its wastewater discharge.
"The ADI-MBR technology has given us excellent results. The effluent quality we are discharging - the effluent is almost crystal clear - has allowed us to completely eliminate our dependence on the county sewer system and the escalating water surcharges we were having to pay each month," Jones said.
About the Author: Jim McMahon writes on water and wastewater systems. His articles have been carried in hundreds of trade publications worldwide. He can be reached at email@example.com.