A study on the relationship between fat, oil and grease (FOG) deposits in sewer systems and FOG disposal patterns

Abstract

Fat, oil and grease (FOG) deposits are one of the leading causes of sewer system blockages, thereby increasing the risks of undesired and polluting flooding and sewer overflows. FOG accumulates throughout the entire sewer network; e.g., in public sewer pipes and lateral house connections it reduces the available discharge capacity, and in pump sumps it increases the risk of pump failures. Previous studies primarily focused on FOG deposits occurring in parts of sewer systems downstream of Food Service Establishments (FSE). It is thought, however, that domestic FOG disposal is also an important contributor to FOG deposits, and therefore warrants further investigation. Consequently, the objective of this research was to investigate the relationship between domestic FOG disposal patterns and the occurrence of FOG deposits in sewer systems. By considering both the household scale and the scale of catchments, it was possible to study the influence of individual and population disposal patterns. The first part of this study focused on the influence of individual disposal patterns; samples of FOG deposits were collected from clogged building drainage systems and questionnaires were conducted to reveal information about the household’s cooking and disposal habits. Only three out of the eleven households showed a link between the cooking fats and oils used and the FOG deposits collected, as their fatty acid profiles displayed similarities. The second part of this study focused on the influence of population disposal patterns on the occurrence of FOG deposits, by studying the severe accumulation of FOG at pumping stations in relation to catchment demographics and sewer system characteristics. Generalized linear mixed model (GLMM) procedures were used to model the probability of the presence or absence of FOG in pump sumps. The model revealed that severe accumulation of FOG in pump sumps was negatively correlated to the average income of inhabitants attached to the catchment, suggesting that individuals within an income-group shared FOG disposal patterns. Furthermore, FSE density and kinetic energy of wastewater per unit of volume per day were found to be important factors correlated with the occurrence of FOG deposits. The results provide important insights into factors that may influence the accumulation of FOG. Further research is required to obtain insights in how particular diets, cleaning habits and FOG disposal patterns may influence the accumulation of FOG.Civil Engineering and GeosciencesWater ManagementUrban Drainag