Lift stations serving high density restaurant and other institutional development tend to have a "perfect storm" for building solid grease on station walls and equipment. In addition to the problems with grease fouling equipment, the anaerobic layer under the grease produces corrosion and odors from hydrogen sulfide and volatile organic acids/mercaptans. Today, I want to discuss best practices for cleaning the lift station once it has heavy accumulation and how to prevent the extensive grease buildup following cleaning.
As with anything wastewater, the first option should be to keep grease out of the sewer lines. To accomplish this, the inspectors need to check for proper grease trap installation and maintenance from upstream restaurants and kitchens. What is proper maintenance? The biggest thing is to get managers and employees to understand the grease trap's importance and function. Once they understand the purpose and how the grease trap is often the source of mystery odors in the parking lot area, people tend to check to ensure proper operation and pumping frequency. Some municipalities ban all grease trap additives - based on data we have collected on BOD, FOG, COD - combining a high quality microbial culture with good maintenance practices will result in less grease going to the collection system and lower pumping costs for the restaurant. The cultures work by initiating biodegradation of grease into short-chain fatty acids - via the beta oxidation process. A biologically treated grease trap (no mixing or aeration) should have no solid grease cap but instead have a clear water with the appearance of fluffy light color grease (actually fatty acids) to indicate the need for pumping.
Even with trap maintenance, long retention time stations can still experience grease buildup from residential and restaurant sources. As soaps and surfactant bound grease sits, the pure grease and long chain fatty acids will start to "break out" and accumulate on surfaces. To clean the lift station with heavy grease accumulation - the last option should be d-limonene or solvent treatment. Why you may ask? Well using a solvent to remove grease buildup releases a slug of grease and fatty acids to the treatment plant downstream. In addition, I have seen heavy use of d-limonene causing severe biological upset at the wastewater treatment plant as high concentrations of many natural plant soaps/oils are toxic to many bacteria.
What should be done? First - clean using pressure washers and an number of non-solvent based cleaners. The downstream treatment plant should be notified of the activity to prepare for higher FOG loading. The idea is to break off the most problematic grease on equipment and floats to prepare for the next step. Instead of using strong chemicals and mechanical cleaning, the lift station can be often maintained using biological treatment. To prevent both odors and grease in lift stations, we have used combinations of aeration and microbe addition. For hydrogen sulfide (H2S) and grease control, I recommend first evaluating an microbe addition. They can be added via manual dose, metering pump, or in solid block form. I have had best results with most control options with metering pump option. If odors are still a problem from H2S coming from feed lines, the addition of aeration or upstream nitrate addition my be needed. Aeration using atmospheric oxygen is usually the lowest cost option over pure oxygen, hydrogen peroxide, or nitrate.
As with grease trap additives, a high quality lift-station microbial product will contain organisms capable of beta-oxidiation of long chain fatty acids. In some heavy FOG lift stations, it may be necessary to add a small amount of surfactant with the cultures to encourage biological activity We do this same process in soil remediation to improve bacteria access to insoluble fatty acids. What happens in the lift station is the bacteria start the biological degradation process that will be finished downstream in the aerobic and anaerobic biological treatment units. By converting a long chain, insoluble fatty acid to shorter chain fatty acids, the "grease" will not solidify and becomes more amenable to degradation by organisms without extensive beta oxidation metabolic capabilities.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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