Purification capacity of natural biofilms and their physiochemical and biological properties: a case study in the Jishan River, a heavily polluted river

Natural biofilms, which are widely distributed in various aquatic environments, can not only serve as bioindicators of various anthropogenic contaminants but also participate in the purification and degradation of various pollutants. However, the inherent purification capacity of natural biofilms and their physiochemical and biological properties are still poorly understood. In this study, outdoor sampling and indoor experiments were used to explore the purification abilities of natural biofilms. The physiochemical and biological properties of natural bio-films were further investigated to reveal their purification mechanism. The results demonstrated that natural biofilms had an excellent purification effect on heavily polluted water. Indoor experiments showed that the purification capacity of natural biofilms was dominated by microbial biodegradation rather than physical biosorption, and after 14.0 days of incubation, the removal rates of COD, TP, NH4+-N, and NO3--N could reach 93.6, 80.83, 85.93, and 81.03%, respectively. The SEM, FTIR spectra, and component analyses revealed that natural bio-films were mainly composed of polysaccharides and proteins. The dominant phyla in the bacterial community structure were Campilobacterota, Proteobacteria, Bacteroidota, Firmicutes, and Desulfobacterota, and the major phyla in the fungal community structure were Chytridiomycota and Ascomycota. These microorganisms might be the main degraders of riverine pollutants.