Design Criteria for Aerobic Treatment of Grease Waste by Filamentous Microorganisms in Activated Sludge

The focus of this investigation was the determination of design and operational criteria for the aerobic biological treatment of grease waste. The aerobic biological treatment is intended promote filamentous organisms, which are capable of degrading oil and grease. Significant amounts of grease waste are generated by different industries. These wastes are recovered in grease traps, oil/water separators and flotation systems. Current practice consists of the recollection of the waste and disposal in a landfill or by incineration. The collected waste has to be disposed of either placing it in a landfill or by incineration. Additionally a change in landfill legislation is anticipated that will make it necessary to treat grease-trap waste. Therefore it is necessary to develop alternative methods for treating these grease-trap wastes.

The design criteria established by this research are:

The treated waste has a density lighter than water; additionally filamentous microorganisms tend to trap fine bubbles therefore floating. In order to maintain thorough contact between the media and substrate, down draft vortex mixing is required. The biological kinetics for the aerobic treatment of grease-trap waste (maximum growth rate, maximum specific rate of substrate utilization, true yield of cell synthesis and the concentration giving one-half the maximum rate). A predictive model for the biological treatment was developed. The research determined that the traditional method of sedimentation was not adequate for the separating the biomass from the liquid phase. In contrast the dissolve air flotation experiments showed that it was possible to reach the treatment goal (300 mg/ l SS). In order to reach this treatment goal it was determined that the air pressure should be 45-70 psi and that the recycle rate should be 30-35%. A economic analysis of the process using the proposed treatment method resulted in an estimated cost of 4570 per 1000 gallons of grease waste.