Image based quantification of solids transport and disintegration processes in sewer pipes

Understanding of sewer gross solids transport and disintegration remains limited, despite their role in blockages and gas formation – issues that are expected to intensify with water-saving measures. This study presents a novel image-based system for quantifying the transport and disintegration of synthetic faecal solids under gravity-driven, part-full flow. The setup comprised a 10 m transparent pipe instrumented with eight high-speed cameras. Solids with 65%, 72% and 85% water content were tested to represent typical faecal properties. A data-driven approach predicted solid velocity, and an existing disintegration model was adapted and validated for realistic sewer flow. Results show that transport depends primarily on water depth, while disintegration is dominated by erosion, enhanced by higher velocity, depth and water content. A velocity threshold of 0.3 m/s was identified below which solids stagnated under shallow conditions (14.5 mm, Froude number (Fr) ≈ 1), consistent with the tested conditions. Findings support improved sewer design for future low-flow scenarios.