Manganese dioxide (MnO₂) nanoparticles influence on the nitrification and anammox activity

The anammox (anaerobic ammonia oxidation) process is one of the most efficient processes of nitrogen removal from wastewater. Although there are some applications of anammox-based technologies, it is still difficult to apply this process widely because of the high optimal temperature around 30-40°C. Thus, the main objective of this study was to evaluate the short-term effects of MnO2 on the anammox and nitrification process activity at a wide range of temperatures between 10 and 30°C, using statistical methods based on the central composite design (CCD). The influence of MnO2 on anammox and nitrification activity, suspended biomass from the laboratory-scale sequencing batch reactor (SBR), and activated sludge from WWTP, respectively, was used. MnO2 concentration range was set between 15 and 85 mg/L, and the temperature range was set between 10 and 30°C. Anammox and nitrification process activity was measured based on the batch test and oxygen uptake rate (OUR), respectively. The results were statistically analyzed. Results revealed that nanoparticles can slightly improve anammox activity by several percent, by up to 10%, but in most cases MnO2 influence was insignificant. The optimal concentration for the anammox stimulation at temperatures below 20°C was evaluated between 40 and 60 mg/L, corresponding to 36 and 56 mg/g VSS. Manganese oxides contribution in the nitrogen removal processes was proved and they should be considered in the field of the anammox process. Thus, further studies are suggested to investigate the long-term effects of MnO2 on the low-temperature anammox process, overcoming possibility of inhibition.