There and Back Again: Grease's Tale from Table to Table
When you think about recycling in restaurants you probably think of composting kitchen scraps or recycling cardboard delivery boxes or maybe recovering bottles and cans after customers are finished their drink. What is less thought of as a material to be recycled is waste grease. This isn't the leftover frying oil that can be recycled into a fuel for powering engines, the grease we're talking about is the stuff that winds up in the waste water of a facility. This can include in the water for washing dishes, the drains of self-cleaning fume hoods, floor drains and any other source where grease is removed from a surface and put into the sewer system.
Just as with other sources of waste, this grease contains a high amount of potential energy that can be converted into a useful product if it is recovered and treated properly.
The process has several stages. First the grease must find its way into the waste system. In South Australia, a permit is required to be issued by SA Water in order for waste water to be put directly into the sewer system. Before waste water may reach the sewer system, it passes through a grease trap, or grease interceptor. Grease traps are essentially large concrete underground containers ranging between 400 litres and 1900 litres in capacity. It is absolutely mandatory that all restaurants contract a grease trap cleaning and pumping company on a regular basis or SA water will intercede with fines or worst case they can close a premises down.
Once inside the grease trap, the greasy water is given a chance to settle. This allows food particles and/or grit to sink to the bottle while oil and grease floats to the surface of the grease trap. The water then flows into another compartment where it settles for a second time to further separate grease and food particles. The somewhat cleaner waste water then flows directly into the sewer system. Adelaide alone has 8,700 km of sewer pipes running underneath its vibrant metropolitan area. On a daily basis, Adelaide's three waste water treatment plants process over 250 megalitres of waste water.
Grease traps typically need to be cleaned every three months by a liquid waste specialist. The process for grease trap cleaning requires a vacuum liquid waste truck. The grease trap's cover is removed and a hose is connected to the grease trap so that all of the liquid waste may be pumped into the truck. Then the grease trap is cleaned and washed with low pressure water. Finally, the grease trap cover is replaced and a perfume is sprayed on the ground. Once this step is done, the liquid vacuum waste truck operator completes all SA water and EPA required documentation then the grease trap cleaning process is complete. The same process is used for septic tank pumping and cleaning.
The liquid waste that has been pumped into the truck is then brought to a processing and treatment plant. We at Signal Waste and Recycling have partnered with various specialists to treat the liquid waste that was removed from grease traps in Adelaide and surrounding areas. The liquid waste is placed in large concrete pits where any remaining water may evaporate. Sawdust is added and mixed into the greasy rubbish, followed by wood chips and peat moss. The mixture is given time for micro-organisms to break down the grease and food particles. Once this process of decomposition is complete, the remaining product is garden mulch which is subsequently used to help grow more food, bringing the cycle full circle. This process can continue indefinitely.
There are several key economic and environmental benefits to using grease traps. The main economic benefit is that sewers will require fewer maintenance and repairs when grease traps are used. Since warm grease will cool once inside the sewer system, it can build up, create blockages and cause sewage backups and flooding to businesses, surrounding areas and local rivers. Therefore, it's extremely economically beneficial to use a grease trap and to service it properly and regularly. Additionally, rubbish removal in Adelaide and SA at large, whether it be in the form of liquid or solid waste, provides employment for local citizens.
From an environmental perspective, the benefits of using grease traps to collect and recycle grease are two-fold. First, the liquid waste that is cleaned out of the grease traps is doesn't end up in our ocean. Grease traps and grease trap pumping reduces the amount of nutrient rich runoff into our oceans and water catchment areas. Secondly, when it is brought to a specialized treatment plant to be decomposed and converted into mulch, it is serving an extremely important role in the agricultural industry. Agriculture is extremely demanding on soil, since growing food requires that plants take nutrients out of the soil in order to produce what we eat. Unless we replace these nutrients in the form of mulch or fertilizers, plants won't be able to grow effectively and eventually won't be able to grow at all.
So the next time you're in a restaurant and you think of the grease trap below your feet, remember how it keeps the sewer system flowing, provides employment, reduces nutrient rich runoff into our oceans, rivers and water catchment and provides more food for the generations to come.