Identifying the Real Sources of FOG in the Collection System

In response to operator concerns about FOG causing obstructions and maintenance in the sludge lines at the City of Longmont’s wastewater plant (WWTP), the City of Longmont’s pretreatment and laboratory staff performed a multi-year study to identify sources and loadings of FOG in the collection system. The study analyzed influent loadings and internal waste streams at the wastewater plant and flows and concentrations in the City’s sewer collection system to correlate FOG production with different user classes (domestic, industrial, commercial). The results of extensive influent sampling showed that domestic users were (and still are) the main source of FOG. As a result, the City decided to continue its existing grease disposal education program for residential users. As a side benefit, the conventional pollutant data collected during the study provided the justification to eliminate the commercial user surcharge for excess conventional pollutants.