Rapid enrichment of anammox bacteria and transformation to partial denitrification/anammox with nitrification/denitrification sludge

The stable nitrite (NO2--N) generation and rapid startup of anammox-based process are the main bottlenecks hindering its application in mainstream municipal wastewater treatment. In this study, a Partial-Denitrification (PD) system re-ducing nitrate (NO3--N) to NO2--N was rapidly developed within 40 days, using the nitrification/denitrification sludge from wastewater treatment plant. The NO3--N to NO2--N transformation ratios achieved 80.6 %. Significantly, a fast self-enrichment of anammox bacteria in this system was subsequently obtained, resulting in the successful transforma-tion to an efficient PD/Anammox (PD/A) process after 79-day operation. The total nitrogen removal efficiency in-creased from 12.4 % to 90.0 % with influent ammonia and nitrate of 45.9 mg N/L and 62.2 mg N/L, corresponding to the anammox activity significantly increasing to 6.0 mgNH(4)(+)-N/g VSS/h without seeding anammox sludge. Abun-dance of anammox increased from 6.7 x 10(8) to 2.0 x 10(11) copies/g dry sludge. High-throughput sequencing results showed that Candidatus Brocadia was the only known anammox genus and accounted for 1.08 % during the PD/A stage. Functional bacteria for PD, assumed to be the Thauera, was enriched from 1.99 % to 60.06 % but decreased to 32.49 % during the improvement of anammox activity. It demonstrated that the PD system with stable NO2--N accumulation enabled a rapid self-enrichment of anammox bacteria and sufficient nitrogen removal with ordinary nitrification/denitrification sludge. This provides new insights into the scaling application of anammox by integrating PD with shortened startup periods and improved TN removal efficiency.

Automated summary

The study developed a Partial-Denitrification (PD) system that rapidly reduced nitrate to nitrite within 40 days, using nitrification/denitrification sludge from a wastewater treatment plant. After 79 days of operation, the system achieved a successful transformation into an efficient PD/Anammox (PD/A) process, with significantly increased anammox activity and nitrogen removal efficiency. The study provides new insights into the scaling application of anammox by integrating PD, shortening startup periods, and improving TN removal efficiency.