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Two parallel trains of completely mixed anaerobic fermenters, 300 gal, coupled with gravity thickeners, 90 gal, were operated to ferment primary solids (PS) and grease trap waste (GTW) from the Nansemond Treatment Plant in Suffolk, Virginia. A control treatment train was fed only primary solids at a targeted organic loading rate of 10kg COD/m 3 /d while the experimental train was fed an elevated lipid load, an additional 20% COD load as grease trap waste (GTW), collected from the grease trap waste stream being disposed of at the treatment facility. The desired effluent product was a low solids, high readily biodegradable COD (rbCOD) and volatile fatty acids (VFA) stream that could be used for biological nutrient removal. At present the primary sludge has been found to have a particulate COD to soluble COD (sCOD) conversion rate of 6 to 15%. However, the amount of effluent sCOD contributed by VFAs (C2:C6) ranges from 25 to 80% depending on reactor operational parameters, while the contribution of acetic acid ranges from 20% to 40%. The incremental degradation of the added lipid load was also far below desired expectations at only 6 to 8%. Modifications are required to effectively transform the grease trap waste in a low pH, 5.2-5.5, anaerobic fermenter.

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Grease trap waste (GTW) is the fat, oil, grease, and food particle containing wastewater that is removed from food service establishment grease abatement devices. GTW is ubiquitous, has high volatile solids (VS) content, high chemical oxygen demand (COD) content, and relatively low nutrient content. Consequently GTW has received a lot of publicity for its ability to increase anaerobic digester gas production when co-digested with municipal sewage sludge. However, these same characteristics (high COD and low nutrient content) also make GTW a candidate for fermentation to produce readily-biodegradable COD (rbCOD) like volatile fatty acids (VFAs) for use as a carbon source for denitrification.