Sewer sediment adhesion reduction and hydraulic floating promotion by alkaline treatment

Deposition of sediment in sewers decreased flow capacity, with harmful gases and pipe erosion. Sediment floating and removal remained challenges due to its gelatinous structure, which induced strong erosion resistance. This study proposed an innovative alkaline treatment for destructuring gelatinous organic matters and improving hydraulic flushing capacity of sediments. At the optimal pH 11.0 condition, the gelatinous extracellular polymeric substance (EPS) and microbial cells were disrupted, with numerous outward migration and solubilization of proteins, polysaccharides and humus. The aromatic protein solubilization (tryptophan-like and tyrosine-like proteins) and humic acid-like substance deconstruction were the major driving factors for sediment cohesion reduction, which disintegrated the bio-aggregation and increased the surface electronegativity. Meanwhile, the variations of functional groups (CC, CO, COO-, CN, NH, C-O-C, C-OH, OH) also contributed to the interaction breakage and glutinous structure disruption of sediment particles. It was found that the rising pH conditions reduced sediment adhesion and promoted particle floating. Solubilizations of total suspended solids and volatile suspended solids were increased by 12.8 and 9.4 times, respectively, while the sediment adhesion was reduced by 3.8 fold. The alkaline treatment greatly improved sediment erosion and flushing capacities under shear stress of gravity sewage flow. Such sustainable strategy only cost 36.4 CNY per sewer meter length, which was 29.5–55.0 % of the high-pressure water jet flushing and perforated tube flushing approaches. [Display omitted] •Alkaline treatment impaired erosion resistance and promoted sediment floating.•Gelatinous EPS interlaminar migration and cell lysis destroyed sediment structure.•Endogenous organic matter dissolution was clarified from molecular interaction.•Humus and protein in EPS played crucial roles in driving sediment adhesion.•Hydraulic sediment erosion promotion pattern and engineering benefit were revealed.