Kinetic characteristics and bacterial structures in biofilm reactors with pre-cultured biofilm for source water pretreatment

•Ammonia and organics removal was enhanced in source water pretreatment systems.•Biofilm of ESM carrier was much easier to accommodate oligotrophic conditions.•AOR was positively related to ALR and did not obviously affected by temperature.•Long-term acclimatization to oligotrophic niche increased biodiversity of biofilm.•Decreased functional bacteria were replaced by others with similar function.

The growth and accumulation of functional bacteria were limited due to the deficiency of substrates in biofilm reactors for source water pretreatment. In this study, pre-cultured biofilm (PCB) formed on different carriers was used to treat oligotrophic source water, and the kinetic characteristics and bacterial structures was evaluated under realistic conditions. Experimental results showed that PCB formed under substrate-enhanced conditions decreased substrate affinity of biofilm, but effectively improved the operation performance of biofilm reactors. In particularly, biofilm formed on elastic stereo media had the lowest apparent half-saturation coefficient (Ks) for substrates, which was more easily to accommodate oligotrophic niche. Interestingly, biodiversity of biofilm was obviously increased after long-term exposure to oligotrophic niche, and decreased functional bacteria were replaced by others with similar function. Basically, Proteobacteria and Planctomycetes were dominant in biofilm samples under both substrate-enhanced and oligotrophic conditions.