What substance is known to cause obstructions in the sewer system?

Settleable solids are a significant contributor to obstructions in the sewer system. These solids, which include materials like sand, silt, and organic debris, can accumulate in pipes and other infrastructure when they settle out of wastewater. Over time, this accumulation can lead to reduced flow rates or even complete blockages, requiring maintenance interventions to clear the lines and restore proper function.

Heavy metals, while they can pose environmental and health risks, typically dissolve in wastewater and do not accumulate in a way that causes physical blockages in sewer systems. Oils and greases can sometimes lead to problems, but they primarily create slick surfaces rather than solid obstructions. Flammable oils pose safety concerns but do not primarily contribute to the physical blockage of sewer lines like settleable solids do. Therefore, settleable solids are a primary concern when it comes to ensuring the smooth operation of sewer systems.