Influence of improper disposal on FOG deposition: Rheological behaviour and pumping power requirements in sewer...

Residents often perceive kitchen sinks and toilets as convenient disposal points for substances like leftover food particles, used cooking oil (UCO), tissues, wet wipes, and other sanitary products. However, this practice significantly contributes to the formation of fatbergs, leading to blockages in sewer lines. Previous studies have mainly utilised aqueous solutions containing specific inorganic constituents, leaving the mechanisms of fat, oil, and grease (FOG) deposit formation in complex wastewater containing both organic and inorganic matter largely unexplored. This study aims to (i) examine how organic and inorganic constituents, food particles and sanitary products impact FOG formation and (ii) perform rheological analysis and modelling to determine the properties of FOG deposits and evaluate the pumping power needed to prevent blockages. FOG deposit formation was studied in a batch process using UCO, and the amount of the deposits produced was expressed as mass per volume of UCO added. Results showed that alkaline hydrolysis at pH 9 promoted FOG deposition by 57.2 % (1.80 mg/mL UCO) compared to acidic pH 5 (1.11 mg/mL UCO). Wastewater-containing organics slightly enhanced the amount of FOG deposits, likely due to the reactions between Ca and carbohydrate source, as indicated by a significant increase in Ca content. Wet wipes and facial tissues substantially increased FOG deposits, reaching concentrations of 5.59 mg/mL UCO and 4.10 mg/mL UCO, respectively. This was attributed to the aggregation caused by their large, porous fibre structures, which effectively trap sewer solids. Based on friction loss and pressure drop, a pumping power over 55.6 W would be required to pump out FOG deposits containing facial tissues and wet wipes along a 15 m long, 100 mm diameter sewer pipe. This study highlights the impact of improper disposal practices on FOG formation and sewer system inefficiencies, emphasising the need for better waste management.