Influence of physical, biological cohesions, oil and grease on the incipient sediment motion in sewerage pipes

Sediment with varying sizes is transported through runoff, finding ways into sewerage pipes and deposited at low-velocity sections. As wastewater is high in organic content, biofilm formed on the deposited sediment, cementing the deposition and resulting in difficulties in the removal from pipes. High concentration of oil and grease in domestic wastewater promotes strengthening the cementing process of the deposited sediment. The presence of silt in the sediment distribution promotes physical cohesion, whereas biofilm through Extracellular Polymeric Substances (EPS) provides microbial cohesion. Thus, this study attempts to investigate the incipient sediment motion of sediment mixture with a different fraction of fine sand-silt, presence of biofilm through variation of EPS concentration, 0–0.1% and percentage of oil and grease (O&G) at 0–10%. The analysis showed that physical cohesion is more critical than microbial cohesion, with the presence of O&G posing the least significant on the changes of incipient sediment motion.