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Wastewater treatment facilities deal with a large number of operating and maintenance concerns, and “Figuring Out Good” solutions to problems, and in particular, fats, oils and grease (FOG) problems can be challenging. The chemical composition and characteristics of FOG result in an inherent difficulty with its treatment, and its impacts to WWTP processes are key to addressing concerns.

The magnitude of the ongoing issues and the expected impacts of FOG to a regulation-mandated treatment process upgrade for the Miami-Dade Water and Sewer Department's (MDWASD) South District WWTP offer a unique opportunity for defining and addressing concerns with FOG. Similar problems with FOG are common to many wastewater treatment facilities. At Miami, piping system plugging, instrumentation fouling, aesthetic issues, and sand filter effluent polishing system clogs were incurred.

The atypical observance of FOG fine particles throughout the treatment process and the potential for plugging of the effluent disposal deep injection wells were also concerns, and strongly suggested the need for a study to identify FOG-related upgrades. With impending expansion of the facility from a 225 mgd peak hourly flowrate capacity to 450 mgd, and with the addition of a filtration process for effluent polishing, the magnitude of potential problems with FOG represents a very serious concern for the MDWASD.

These considerations in conjunction with the significant amount of septage and landfill leachate handling at this facility resulted in the implementation of a specialized sampling and characterization program. FOG concentrations were measured not only at the sources (WWTP influent, septage, leachate), but also at each key component in the treatment process. Characterization indicated domestic influent levels that were similar to typical domestic WWTP's, but indicated extreme variations in levels of FOG associated with the septage discharges. Characterization also showed relatively successful reduction of FOG levels through the biological treatment process. However, despite the reductions by the microbiological treatment process, the presence of FOG, and especially fine FOG particles was quite evident, and FOG issues were prevalent. Process reviews and characterizations defined the presence of a FOG recycle loop around the secondary clarifiers. Elimination of this loop for a relatively short demonstration period, during the characterization efforts, did not significantly affect FOG levels or issues.

Based upon data collected, FOG removal and treatment alternatives were developed, and a qualitative review was completed. After screening numerous alternatives, the potential improvements were reduced to basic full-stream FOG treatment process additions, compared with enhancements to existing unit processes. Immediate remedial improvements were implemented, including elimination of recycling of skimmings, as well as improvements to the existing sand filters. For the long term, recommendations included an improvement program to upgrade the secondary clarifier scum removal system, followed by immediate scum withdrawal to off-site disposal, and the addition of a Septage Receiving, Treatment, and Equalization Facility. Further, for flexibility of FOG handling, mixing of the FOG with the plant's waste sludge, followed by concentration and anaerobic digestion will be tested for potential future implementation.
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Document Type: Research Article

Publication date: 2005-01-01

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