Impacts of Chosen Parameters on Fe-Dependent Nitrate Reduction in Anammox Consortia: Performance and Bioactivity

Nitrogen removal from mature landfill leachate through enhanced Partial Nitrification-Anammox process in an innovative multi-stage fixed biofilm reactor

In the current integrated PN/A method/process for mature landfill leachate treatment, microbial inhibition and low nitrogen removal capacity are the big barriers due to high ammonia concentration and low C/N. This study aimed to evaluate the performance of a high-rate nitrogen removal lab-scale reactor, which combines pre-denitrification and Partial Nitrification-Anammox (PN/A) in a multi-stage fixed biofilm reactor (MFBR), for mature landfill leachate treatment. A nitrogen removal efficiency (NRE) of 90.43 % and an average nitrogen removal rate (NRR) of 0.94 kg/m³·d were observed at an influent NH+ 4-N concentration of 2274.39 mg/L during the last operational phase. The nitrogen mass balance showed that the nitrogen concentration gradually decreases along the course, and nitrogen was mainly removed in the aerobic chambers, in which Anammox contributed to 86.4 % of the removed nitrogen, while the front anoxic chamber is mainly used to remove NO- 3-N from the recirculation. Redundancy analysis showed that the variation in NH+ 4-N concentration along the course was the main factor affecting microbial community succession, which shows that the reactor configuration enables efficient cooperation and distribution of different microorganisms. Moreover, economic analysis of MFBR process showed that the energy consumption and carbon addition were reduced by 58.9 % and 100 %, respectively. Therefore, the MFBR established in this study, with its new configuration, achieves efficient treatment of landfill leachate in a single reactor and is environmentally friendly, and could be considered as a reference for full-scale landfill leachate treatment.

The effects of Fe(III) and Fe(II) on anammox process and the Fe-N metabolism

This study aims to compare the effects of different Fe stress on anammox (anaerobic ammonium oxidation) process, therefore seven identical reactors were operated under different Fe(II)/Fe(III) concentrations. After 38 days of operation, the anammox activity was highest (10.49 ± 0.41 mg-TN/(g-VSS·h)) under conditions of 5 mg/L-Fe(II), while under 30 mg/L-Fe(III) displayed severe inhibition. The results showed that continuous addition of 30 mg/L-Fe(III) would damage the composition of EPS (extracellular polymeric substances) and make anammox bacteria more sensitive to environmental stress. While high Fe(II) concentrations could result in precipitates encasing granular sludge, affecting substrate utilization. Moreover, the results of ΔNO₃^--N/ΔNH₄⁺-N indicated that Fe(II)-dependent nitrate reduction was induced in reactors added with Fe(II). OM27_clade and norank_f__Burkholderiaceae might be candidates for this process according to the correlation of genera and functional genes (based on the PICRUSt 2 functional prediction). Overall, this research is expected to provide new ideas to the effects of Fe(II)/Fe(III) on anammox and to the practical application of coupled system based on anammox in wastewater treatment.