Pipe material significantly affected microbial regrowth and potential risks in reclaimed water distribution systems

Abstract

Secondary pollution and microbial risks pose significant challenges to reclaimed water distribution systems (RWDSs). This study conducted 140 d investigations on temporal variations in water characteristics, microbial regrowth and communities in RWDSs with different pipe materials, including ductile iron (DI), cement mortar lined ductile iron (CI), polyethylene (PE), and Q235B carbon steel (CS). It was demonstrated that microbial community was significantly influenced by bacterial phase. Candidatus_Kaiserbacteria, Legionella and Mycobacterium were relatively abundant in bulk water and effluent, while Hyphomicrobium, Gordonia, and Sphingobium were significantly enriched in pipe-wall biofilms. With respect to the influences of pipe materials, PE system demonstrated superior performance in microbial regrowth control and water quality maintenance compared to DI, CI, and CS systems. The relative abundances of pathogens and disinfection-resistant bacteria in PE system were significantly lower, and corrosion-associated bacteria were markedly abundant in DI and CS systems. These results demonstrated lower potential microbial risks and higher practical advantages of PE pipe. Redundancy analysis and Mantel test revealed microbial communities correlated well with extracellular polymeric substances and reclaimed water characteristics (p < 0.05). This study provided valuable insights into microbial risk control and pipe material selection for safer wastewater reclamation.