Grease Trap Treatments

Fats, oils and grease (FOG) in sewer systems are a problem in many cites due to the increase in the number of restaurants. Furthermore, with aging sewer systems in many metropolitan areas, the problem is amplified. By effectively managing the dissolved oxygen (DO) levels and implementing a bioaugmentation program, commercial operations can significantly reduce the FOG that builds up in the grease interceptors (traps). Significant reductions in the soluble BOD and TSS effluent going to the sewage treatment system are the result.

Without the use of a grease trap there, is no simple way to prevent FOG from being carried into the sewer system, wet wells or lift station(s). With proper training of the kitchen personnel, grease trap waste loading can be minimized and will help prevent large quantities of FOG from entering the interceptor and sewer lines.

Federal Document 40 CFR 403.5 regulates and prohibits the introduction of non-biodegradable hydrocarbons into the sewer systems. Limited or no general regulations are in place on other edible cooking fats, oils, or grease, (FOG’s). The regulation of FOG commonly sent to the sewer system is left to the local jurisdiction. The rules are not consistent and are sometimes arbitrary and cumbersome for the restaurant to be in compliance. Furthermore, many local municipalities impose limits that result in surcharges on discharge water to the sewer system.

Passive grease interceptors collect the fats, oils and grease (FOG) as it rises to the top of a baffled chamber when wastewater passes through the unit. The grease trap influent separates because grease and water are immiscible; creating a grease cap due to the difference is specific gravity of the grease (lipids) and water. The FOG that is intercepted must be manually removed from the grease interceptor. This is done by staff personnel in smaller operations or may be subcontracted out to cleaning companies or by grease rendering companies. This collection/disposal option can be a significant expense to most commercial operations.

A pre-cast concrete grease interceptor is a larger interceptor that is designed to collect the fats, oils and grease (FOG) in the same manner as a smaller passive grease interceptor, only on a much larger scale. The most popular sizes are 750 to 2,000 gal. Pre-cast concrete grease interceptors are more expensive to install and collection/disposal costs are becoming more and more expensive to maintain.

For the purpose of this discussion, we are more concerned about the pre-cast type of interceptors and larger grease trap designed to catch and hold (FOG), preventing the down flow into the sewer piping. The mixed liquor coming from a restaurant kitchen includes water, cooking waste, soaps, micelles (detergents), solvents, di / triglycerides and fatty acids. The internal surfaces of the grease interceptor along with the pipe walls in sewer lines provide opportunities for the organic materials to buildup.

The only effective way to reduce the buildup of the FOG’s in commercial grease interceptors is to:

• Properly manage and control the dissolved oxygen (DO) level using a properly designed and maintained aeration system (AeroClear™) in the grease interceptor(s).
• Introduce a Bioaugmentation program utilizing a targeted waste digestant to metabolically convert the contaminated wastewater (FOG’s) into water and harmless gas.

Note: Routine pumping of the grease cap relocates the volume buildup problem: however, does not address the buildup on the walls and piping.

By increasing the levels of dissolved oxygen (DO) within the commercial grease interceptors, the process becomes more efficient in reducing and digesting the FOG’s. By increasing the efficiency of the overall system, significant soluble BOD and TSS reductions are realized. These on-site reductions can benefit both the commercial establishment and the waste treatment facilities.

Significantly higher oxygen levels within the grease interceptor also assist in preventing the more acidic effluent conditions normally found under typical anaerobic grease interceptor environments, thereby benefiting the overall sewer system downstream of the commercial interceptor. Most municipalities have permitted limits and monitor pH of the effluent discharged from commercial food preparation and processing operations.

Bioaugmentation is the introduction of highly efficient natural microbial strains grown in environmentally controlled fermentation processes that are inoculated into the waste grease interceptor system to treat contaminated wastewater. These highly effective microbes use the simple and complex carbohydrates as a food source yielding water and carbon dioxide. In grease interceptors, bioaugmentation is used to ensure that the in situ microorganisms that are selectively chosen to efficiently degrade or digest the (FOG) contaminating the wastewater maintain the dominant population culture and most efficient microbes.

Regarding some of the technical issues, we are concerned about an in situ grease trap containing water, fatty acids, proteins, other nutrients and inhibiters like chlorine and other compounds used for cleaning are not beneficial. The use of inhibitors like chlorine should be minimized but in general, the commercial cleaning compounds used for norma l housekeeping are diluted or neutralized by the organics. Overuse of cleaning compounds will inhibit or kill microbial activity.

We will consider three (3) main components in commercial food service waste water to include the following:

• Simple Carbohydrates, Starches, and Sugars
• Lipids (FOG) which are usually triglycerides and long chain free fatty acids(C10-18), along with proteins
• Minerals and water

The normal fluid flow into the grease trap during operations provides some mixing and entrained oxygen in the wastewater even though the lipids are immiscible and will separate and float. As the oxygen level rises, the system becomes aerobic, which demands more oxygen as the population increases, however, because of the constant changes within the interceptor, parts the system must operate in an anoxic or anaerobic environment. Under anaerobic (lacking oxygen) conditions, undesirable microbial populations flourish producing hydrogen sulfide, methane, ammonia, mercaptans notwithstanding a much slower digestion rate. In some cases the aerobic and facultative microbes are suppressed resulting in butyric acid, putrid odors, low pH, and toxic gases. As the grease cap builds, the cap inhibits good mixing and oxygen transfer. If you have ever been near the grease trap when it is being pumped out, the case is clearly made by the rancid odors.

Forcing the system to become and remain aerobic (excess dissolved oxygen) can be easily achieved by augmenting and dispersing air into the first chamber of the grease trap. Another added benefit, if properly configured, is the introduction of the micro air bubbles into the system separating the lipids from the water, floating them to the top, thereby minimizing the “down streaming” of the FOG particles. Commercial food processors utilize similar dissolved air flotation (DAF) to accomplish this lipid separation.

Since the grease interceptor contains “dirty water”, due consideration must be given when designing the air injection device. Simple pipes with holes drilled into the perimeter are not very effective and difficult to measure the resulting oxygen transfer rates with any reliability. It is, therefore, imperative that a proven aeration system be integrated into the grease interceptor liquid medium to assure the desired results. Controlled aeration of a grease trap will not change the volume or the residence time for the liquor to be held within the interceptor.

The effective balance of the system is accomplished by routine addition of specific microbes that thrive and survive in this lipid rich environment to assure dominance to do the work. They are optimized in the aerobic cycle.

Simple carbohydrates like sugar and most starches that are present provide immediate metabolic energy sources for the microbes. The microbes recognize the need for lipase, the enzyme key that breaks the long chain lipid into a friendlier molecule like glycerol. Co-enzymes and other nutrients, primarily the lipid soluble type, are involved in the catabolic pathway (breaking down larger molecules, commonly involve oxidative, exothermic reactions) yielding reducing equivalents.

Step one involves the Fatty Acid Oxidation (Lipogenesis). Lipids inherently contain more energy (about double) than simple carbohydrates. Since they are hydrophobic, they need to be hydrolyzed by enzyme hydrolysis to become activated. To get real specific, the process is complicated with many intermediate steps. Summarizing the basics, oxidation of the lipids to acetyl CoA (The precursor to ATP) for use the mitochondria of the bacterium cell (engine and energy source) is initiated. Because the system conditions are optimized by bioaugmentation with the correct nutrients,(bacteria, and dissolved oxygen), the Krebs cycle or (citric acid cycle) is established and encourages carbon dioxide and water by-products. Microbe cell numbers and bodies multiply. Providing the nutrients are available, the cell production rate will cause the population to increase doubling every 30-60 minutes. The end result is grease conversion from a messy problem to simple compounds, e.g. water and carbon dioxide. How much more environmentally friendly can it get? By Increasing the DO (dissolved oxygen) with the AeroClear™ and dosing with the proper strains of microbes, Bio-B2 Series Grease Trap Treatment, we can very quickly digest and consume the FOG’s present in commercial grease interceptors.

Specially formulated REX-BAC-T® microbes have a higher survival rate when the system is exposed to unfavorable conditions. The correct bacteria adapted to the grease rich conditions have been shown to benefit the downstream discharge liquor composition into sewer laterals, wet wells, lift stations and the main trunk lines. The integration of REXBACT® AeroClear aeration technologies and the use of highly effective concentrated Bio-G2 products provides the commercial establishments and municipal treatment plants assurance that the grease trap problems will be minimized.

Commercial users should participate in a bioaugmentation management program to:

• Reduce the FOG load at the municipal treatment plant
• Protect the hundreds of miles of sewer lines from severe clogs. These sewer lines lead directly downstream to the lift stations and wastewater treatment plants.
• Cost reductions to the commercial users and local wastewater treatment facilities.
• Pollution prevention and reduction initiatives.

What about the need to pump the grease interceptor or trap out? Because not all of the discharge compounds that are channeled through the grease interceptor are biodegradable, the inorganic material and grit will need to be pumped out on as needed, but significantly reduced, basis.

Enzymes and surfactants that break down or emulsify and flush the FOG’s downstream generally defeat the main purpose of the grease trap. The overuse of enzymes and surfactants in a grease trap can cause emulsified solids to reform in the public sewer system. The best and most effective way to reduce the buildup of the FOG’s in the grease trap is to:

• Properly manage and control the dissolved oxygen level using a properly designed and maintained aeration system (AeroClear™) in the grease trap.
• Introduce a Bioaugmentation program by using an effective waste digestant to metabolically convert the organics (FOG’s) into water and carbon dioxide gas.