Bio-treatment for Grease Traps Case Study
Many Investa buildings have food courts and cafés at ground level which produce greasy waste. This waste is collected in grease traps, which incur operating costs of around $70,000 per annum. The largest of these is located at 55 Market Street, Sydney which was pumped out every three weeks, at a total cost of over $23,000 per annum.
Wastewater from restaurants and kitchens contains large amounts of fats, oils and grease (FOG) which is immiscible with water and can cause blockages in pipes and sewers. In order to remove the FOG, all restaurant and kitchen wastewater is fed into a grease trap, which consists of a large tank with a series of baffles. Grease is retained at the top of the trap, sediment falls to the bottom, and the wastewater is discharged from an outlet in the middle. When the grease and sediment have built up to a significant level, the trap ceases to be effective, and so must be pumped out.
A well-designed grease trap should retain both grease and sediment, as shown below in Figure 1. The bulk of the sediment is trapped behind the lower baffle, while the grease is left floating on the surface in the middle of the trap. The baffles ensure that any grease or sediment which is entrained in the water stream (particularly at higher flow rates) will also be captured by the trap.
By introducing a bioremediation system to this grease trap, operating costs were significantly reduced. Bioremediation uses bacteria to break down fats, oils and grease, resulting in a cleaner discharge to sewer as well as reducing the required pump-out frequency. The bacteria also help to break down grease in the waste pipes, reducing blockages and accumulated grease deposits.
Working with Environmental Biotech and EP&T, grease and solids levels in the grease trap were monitored for three months after the introduction of the bioremediation system. This data was given to Sydney Water, who then revised the building's Trade Waste Agreement to extend the mandated pump-out frequency from three weeks to 26 weeks representing a saving of almost $14,000 per annum.
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