Performance improvement of raw water pretreatment process with pre-inoculation biofilm: feasibility and limiting factors

The initial formation of biofilm and the removal performance of pollutants in biological pretreatment process for polluted raw water were limited due to the oligotrophic niche in raw water. In this study, the feasibility of using pre-inoculation biofilm formed under nutrients enhanced condition for polluted raw water treatment was analyzed in nine batch reactors. Results showed that the pollutants removal performance of biofilm was improved under nutrients enhanced conditions. Ammonia oxidation rate (AOR) was exponentially increased with the increasing in NH₄ ⁺-N levels, and organic matter removal rate (ORR) was positively related to the initial total organic carbon (TOC) concentration. The biofilm formation and microbial diversity were further improved via adding more substrates, seeding river sediment and feeding effluent from a mature biofilm reactor. However, the biofilm formed under higher substrate conditions had higher half-saturation constant values (K _S) to both NH₄ ⁺-N and TOC, which decreased AOR and ORR values when it was used to treat polluted raw water. The reduction percentage of AOR and ORR showed logarithmic growth modes with the increase in K _S values. Fortunately, improvement of nutrients flux via accelerating influent replacement could enhance the start-up performance effectively and decrease the operation risk introduced by the changes in substrate affinity.