Study and application of real-time control strategy based on DO and ORP in nitritation-denitrification SBR start-up

In this study, nitritation-denitrification SBR was successfully begun within 5 days by maintaining a proper condition (pH > 8, DO 0.1-0.5 mg/L and 29.5 ± 0.5°C) and transient excessive aeration would not cause N-NO₃ ^- accumulation. In the start-up stage, FA had an upward trend and reached to 10.98 mg NH₃/L, which could entirely inhibit NOB. On the basis of experimental evidence, DO and ORP showed regular trends of variation and the first derivatives of DO and ORP as process control parameters in a nitritation-denitrification SBR was proposed. During the real-time control period, N-NH₄ ⁺ in the outlet was less than 2 mg N-NH₄ ⁺/L and N-NH₄ ⁺ removal efficiency was 97%, with nitrite accumulation rate (NAR) reaching 98%. After algorithm optimization by using 'Slope', the first derivatives of DO and ORP curves became smooth and interference signals were eliminated. Pre-aeration could promote nitritation rate from 23.76 mg/L/h to 26.27 mg/L/h and increase the transformation rate of N-NH₄ ⁺ to N-NO₂ ^- from 48.% to 79.6%. The 16S rDNA analysis showed that real-time control could cause a significant difference in microbial community. Nitrosomonas was the dominant strain in AOB and its relative abundance increased from 0.13% to 0.786%. Nitrospira was inhibited and washed out in nitritation-denitrification sludge.