DEALING WITH FOG: A PROBLEM OR AN OPPORTUNITY

摘要

In recent years there has been growing concern for sewer collection system capacity management (CMOM) and the prevention of sewer system overflows (SSOs). One major cause of reduced capacity that promotes SSOs is lines becoming clogged with fats, oils and grease (FOG) discharged into the sewer. How a municipality or utility district deals with FOG can turn this problem into an opportunity. For this reason, the Orange County Sanitation District (OCSD) is developing a plan to reduce the amount of FOG discharged into the sewage collection system through the development of Best Management Practices and enacting future new FOG control ordinances. As a result of improved FOG collection practices and enforcement of these future new ordinances, the quantity of FOG discharged directly at the OCSD Plant No. 1 may increase. This paper presents findings of a recently completed study that evaluated disposal options for FOG, their impact and benefits to in-plant processes. The result of this study has found two alternatives for FOG disposal and treatment at the OCSD plant 1 that will truly convert an environmental problem into a positive opportunity for the district and its rate payers. Processing and disposal alternatives for FOG received directly at the OCSD treatment plants are developed and discussed in this paper. Impacts associated with their implementation are also addressed. Each alternative assumes compliance with new FOG ordinances passed as a result of the BMP study. Alternatives that have been developed include: 1. Base case – status quo (continue current practices of receiving FOG at the plant headworks, removal with primary scum, pumping to anaerobic digesters along with primary sludge) 2. On-site treatment using anaerobic digestion 3. On-site collection and off-site recycling at a grease rendering facility 4. On-site collection and off-site recycling as a bio-fuel 5. On-site collection and off-site landfill disposal Six different criteria were established for evaluating each alternative including: economic impacts, maintenance impacts, staffing impacts, process operation impacts, traffic impacts, and environmental impacts. A workshop was held with OCSD staff to determine the relative weight of each criteria and each alternative was rated on a scale of 1 to 5 with 1 being the least desirable and 5 being the most desirable.