Startup pattern and performance enhancement of pilot-scale biofilm process for raw water pretreatment

• Two pilot-scale biofilm reactors were established with different startup strategies.
• Precoated biofilm carriers favor biomass enrichment and reduce nitrite accumulation.
• The optimum DO level for adequate nitrification was 1.0–2.6 mg L−1.
• The suitable temperature range for adequate nitrification was 21–22 °C.
• The presentence of algae increased the risk of disinfection by-products production.

The quality of raw water is getting worse in developing countries because of the inadequate treatment of municipal sewage, industrial wastewater and agricultural runoff. Aiming at the biofilm enrichment and pollutant removal, two pilot-scale biofilm reactors were built with different biological carriers. Results showed that compared with the blank carrier, the biofilm was easily enriched on the biofilm precoated carrier and less nitrite accumulation occurred. The removal efficiencies of NH4+-N, DOC and UV254 increased under the aeration condition, and a optimum DO level for the adequate nitrification was 1.0–2.6 mg L−1 with the suitable temperature range of 21–22 °C. Study on the trihalomethane prediction model indicated that the presentence of algae increased the risk of disinfection by-products production, which could be effectively controlled via manual algae removing and light shading. In this study, the performance of biofilm pretreatment process could be enhanced under the optimized condition of DO level and biofilm carrier.