Application of sponge iron-carbon to enrich anaerobic ammonia-oxidizing bacteria from sludge mixture and coupled denitrification for degradation of industrial wastewater

For the treatment of industrial wastewater, coupled iron‑carbon micro-electrolysis (ICME) with anaerobic ammonia oxidation (anammox) and denitrification was optimized under the following conditions: Fe/C = 2, C/N ≤ 2, and the temperature was 30 °C. The coupled ICME enriched ammonia-oxidizing bacteria (AnAOB) and denitrifying bacteria (DB) in the mixed sludge on the 76th day of the present experiment. Stable operation was achieved on the 78th day. The COD and TN removal rates during the operation were 86.20 % and 87.12 %, respectively, while the control group (without iron and carbon) had removal rates of 74.30 % and 60.31 % which were 11.9 % and 26.81 % higher, respectively. Notably, the abundance of AnAOB in the system increased from 0.44 % to 1.43 % during the operation from day 76 to day 100. High-throughput sequencing demonstrated that Candidatus_Kuenenia was a key anaerobic ammonia-oxidizing bacterium. Based on the experimental results, the ICME process could rapidly enrich anaerobic ammonia-oxidizing bacteria to change the microbial community structure of the sludge under the water quality conditions of industrial wastewater and increasing the tolerance of certain DB and Candidatus_Kuenenia to water quality. By combining with iron‑carbon, the rapid modification of mixed sludge was achieved, and the iron‑carbon micro-electrolysis coupled denitrification anaerobic ammonia oxidation process was established, which provides a certain reference value for treating industrial wastewater.