Nano Ag-AlOOH modified cured-in-place-pipe (CIPP) composites for controlling sewer biofilm:performance and mechanism of extracellular polymeric substances reduction and antimicrobial activity

The sewer biofilms are recognized as a major reason for odor, pipe corrosion and flow restriction. Ultraviolet-cured-in-place pipe (UV-CIPP) has been a widely used trenchless repair technique in recent years because of their cost-effective and small jobsite footprint. This study compared the physicochemical properties, microbial community structures, and related functional genes of biofilms formed on CIPP, reinforced concrete (RCP) and ductile iron pipes (DIP). The total extracellular polymeric substances (EPS) contents of CIPP, RCP and DIP were 186.5, 286.3 and 214.9 mg/g VSS. Biofilms on RCP exhibited weaker motility and stress responses, whereas those on DIP displayed enhanced adhesion and EPS production. The formation of high ORP microenvironments on CIPP surfaces was not favorable for biofilm growth. The smooth surface of CIPP hindered microbial colonization and caused stressed microorganisms to allocate energy to growth and reproduction rather than EPS synthesis. Furthermore, a new strategy was proposed for effective biofilm inhibition by adding boehmite loaded with Ag nanoparticles (Ag-AlOOH) to the UV-CIPP resin layer. Ag-AlOOH/CIPP reduced biofilm thickness, EPS, protein, and polysaccharide contents of CIPP by 72.1 %, 69.4 %, 68.7 %, and 73.5 %, respectively. The polyhydroxy structure of AlOOH enhanced the hydrophilicity of the CIPP surface and reduced microbial colonization. Ag⁰/Ag⁺ decreased the nitrogen and energy metabolism, limited Gram-positive bacterial abundance, and viable cell counts. This study showed that effects of CIPP materials on biofilm characteristics and microbial functions, and developed an efficient biofilm control strategy by incorporating Ag-AlOOH into UV-CIPP.