Muffin Monster grinder units from JWC Environmental help prevent FOG buildups in a Florida plant, stymieing dangerous sewage overflows
Disposal of fats, oils and grease (FOG) was an ongoing problem for municipalities and utility companies for years. When these thick, gooey substances are allowed to discharge through drains, they congeal inside sewer pipes and cause an overflow. Sewage overflows are health hazards, damaging property and the environment.
After identifying excessive grease buildup as the primary cause of sewage overflows in wastewater systems, federal and state bodies created ordinances to prevent these harmful occurrences. As a result, municipalities across the county have implemented FOG programs to comply with regulations, including methods to reduce the amount of grease in wastewater systems and treat and dispose of collected grease.
Although FOG has long been acknowledged, the recent green movement and emphasis on sustainability has brought a renewed awareness to the problem. More attention is given to pipe clogging prevention methods and ways to reuse.
Because this was a new area of concern, little data existed. The county already operated one wastewater facility that accepted loads from grease haulers. Receiving records indicated that an average of 3,000 to 5,000 gal per day (gpd) were being off-loaded. However, the plant was slated to end service and divert flows to a newer facility several miles away.
“Upon demolition of that plant, it became painfully obvious that the receiving and treatment method that had been employed there was not ideal for grease, and the county sought a better solution for the new facility,” Pineallas County Senior Engineer Mike Engelmann, P.E., said.
At the same time, the topic of biodiesel fuel was increasing in popularity and many independent entrepreneurs were touting their ability to make this type of fuel from grease. The county decided that a separate, centrally located grease collection facility could provide feedstock for biodiesel producers, and construction was planned approximately 10 miles from the treatment plant.
The new facility, called the FOG Plant, was designed to handle and dewater up to 40,000 gpd of raw trap grease. This was based on the number of food preparation establishments, capacity of the traps and frequency of pump outs. It also depended upon the FOG compliance inspection team. Haulers would pump several different grease traps and then offload at this new facility.
An integral part of the new system solution would be grinding/processing equipment. The new system is setup so raw trap grease passes through a sewage grinder before it enters a suction pump and storage tank.
“It's amazing what gets pumped out of a trap, but the [grinder] just chews right through silverware, bones and even bricks from the trap itself,” Engelmann said.
Fuel for the Future
The Muffin Monster also helps protect the rest of the processing equipment, which is setup to dewater the raw trap grease by removing about 85% of the original volume in the form of water and returning it to the sanitary sewer. The thickened grease then gets loaded into a liquid-tight container for shipment offsite.
Due to various political and financial considerations, this thickened product, known as brown grease, did not make a feasible feedstock for biodiesel with today's technology.
Fortunately, brown grease does make for a good source of methane if anaerobic digesters are available. The county decided to try injecting this grease into its egg-shaped anaerobic digestion system. The injected grease significantly increased the digester gas production, which is used to supplement the natural gas requirement in the county’s sludge pelletizing system.
A receiving station was then added at the new treatment plant where the thickened grease is offloaded into a day tank and metered into the digesters.
Similar to the FOG plant setup, a sewage grinder was installed in the offloading line to protect the circulation and rotary lobe metering pumps. Here the thickened grease is continuously circulated through the grinder as the metering system feeds it into the digester. The unit ensures a homogeneous mixture and protects the equipment from any foreign material.
Overall, this approach has proven effective as an environmentally friendly grease disposal location for the community, reducing the county's consumption of natural gas for its pelletizing process.
Cynthia Guardia is an independent technical writer for JWC Environmental. Guardia can be reached at email@example.com.
Images courtesy of Mike Englemenn.