Methanol tolerance and acclimation in the anammox process using a gel carrier

Low-concentration methanol effect on the microorganisms, nitrogen removal, and recovery of the completely autotrophic nitrogen removal over nitrite

Methanol has a significant effect on the performance of the completely autotrophic nitrogen removal over the nitrite (CANON) process. In this research, the effect of low-concentration methanol on the functional microorganisms and nitrogen removal and recovery in the CANON system is investigated. The result shows that the anaerobic ammonium-oxidizing bacteria (AnAOB) was suppressed with low-concentration methanol addition, and the phylum Planctomycetes was hidden. The genus Candidatus Brocadia was restrained, and the relative abundances reduced from 25.5 to 15.0% in the upper biofilm and from 20.3 to 14.3% in the bottom biofilm, respectively. However, low-concentration methanol promoted the nitrifying oxidizing bacteria (NOB) activity. This phenomenon reduced the average ammonium nitrogen removal rate from 95.0 to 70.7%, and the average total nitrogen removal rate decreased from 81.3 to 43.6%, respectively. The results demonstrated that the low-concentration methanol as an organic carbon matter harmed the CANON process. Fortunately, the CANON system had an excellent self-healing ability when the methanol was stopped, with the average ammonium nitrogen removal rate and total nitrogen removal rate returning to 95.5 and 80.9%, respectively. This research supplies a reference for practical engineering design and application by improving the understanding of the effects of low-concentration methanol on CANON process performance.

Nitrogen removal performance and rapid start-up of anammox process in an electrolytic sequencing batch reactor (ESBR)

In this study, the electrolytic sequencing batch reactor (ESBR) with different current densities was constructed to investigate the nitrogen removal performance and rapid start-up of anaerobic ammonia oxidation (anammox) process. The changes of total nitrogen removal rate (TNRR), specific anammox activity (SAA) and nitrogen concentration under different current densities were analyzed, and then the effect of the optimal current density on the start-up of anammox in ESBR was explored. The results showed that ammonium nitrogen removal efficiency (92.7%), nitrite nitrogen removal efficiency (15.5%) and total nitrogen removal efficiency (28.1%) were obtained with the TNRR and SAA were 0.0118 g N L^-1 d^-1 and 0.0050 g N (g Vss d)^-1, respectively under the optimal conditions (i.e., current density = 0.10 mA cm^-2, temperature = 36 °C and pH = 7.6). In addition, the stoichiometric ratio indicated that anammox was initiated successfully for 91 days in ESBR with the current density of 0.10 mA cm^-2, which was shortened by 10 days compared with the conventional SBR without current density. These results suggest that an array of rapid start-up processes of anammox can be developed through applying current density to stimulate the activity of anammox bacteria (AnAOB).

Inhibition of anammox activity by municipal and industrial wastewater pollutants: A review

The use of the anammox process for nitrogen removal has gained popularity across the world due to its low energy consumption and waste generation. Anammox reactors have been used to treat ammonium-rich effluents such as chemical, pharmaceutical, semiconductor, livestock, and coke oven wastewater. Recently, full-scale installations have been implemented for municipal wastewater treatment. The efficiency of biological processes is susceptible to inhibitory effects of pollutants present in wastewater. Considering the increasing number of emerging contaminants detected in wastewater, the impacts of the different types of pollutants on anammox bacteria must be understood. This review presents a compilation of the studies assessing the inhibitory effects of different wastewater pollutants towards anammox activity. The pollutants were classified as antibiotics, aromatics, azoles, surfactants, microplastics, organic solvents, humic substances, biodegradable organic matter, or metals and metallic nanoparticles. The interactions between the pollutants and anammox bacteria have been described, as well as the interactions between different pollutants leading to synergistic effects. We also reviewed the effects of pollutants on distinct species of anammox bacteria, and the main toxicity mechanisms leading to irreversible loss of anammox activity have been identified. Finally, we provided an analysis of strategies to overcome the inhibitory effects of wastewater pollutants on the nitrogen removal performance. We believe this review will contribute with essential information to assist the operation and design of anammox reactors treating different types of wastewaters.