Performance optimization of a chitosan/anammox reactor in nitrogen removal from synthetic wastewater

Anaerobic ammonia oxidation (anammox) is an environmentally friendly, cost-effective, and biological method for nitrogen treatment from aqueous solutions. However, slow growth rate, negative effects of high concentration of nitrite, ammonia and other pollutants (such as metals) on anammox activity are the main drawbacks of using anammox. Thus, in this study, anammox was attached on chitosan to improve anammox performance. Two reactors comprising chitosan and anammox bacteria (first reactor, chitosan/anammox) and solely anammox (second reactor, control) were run for 73 d. The nitrogen loading rate (NLR) varied from 2 to 14 (gN/L/d), while the nitrogen concentration varied from 80 to 700 mg/L. The chitosan/anammox reactor showed a better performance than the sole anammox (control), with respective maximum abatement values of ammonia (NH4+), nitrite (NO2-), and total nitrogen (TN) of 90.8%, 83.5%, and 81.7% on days 20-25 under a NLR of 8-10 kgTN/(m(3) d). Response surface methodology (RSM) was employed to optimize the performance of both reactors, and a reasonable R-2 value showed that the RSM well optimized the performance of the reactors. After finding the optimum performance conditions for both reactors, Fe and Cu (0.5-7.0 mg/L) were added to the influent to monitor the effects of metals on the performance of both reactors. The performance of both reactors decreased to 0% following the addition of 7.0 (first reactor) and 6.5 (second reactor) mg/L Cu and Fe, respectively. This indicated that chitosan not only enhanced nitrogen removal by anammox but also improved the resistance of anammox to metals.

Automated summary

Anaerobic ammonia oxidation (anammox) is an environmentally friendly and cost-effective method for nitrogen treatment, but has drawbacks such as slow growth rate and negative effects of high concentrations of nitrite, ammonia, and other pollutants. This study found that attaching anammox to chitosan improved its performance, with the chitosan/anammox reactor showing better nitrogen removal efficiency compared to the sole anammox reactor. Additionally, the study demonstrated that chitosan not only enhanced nitrogen removal by anammox but also improved its resistance to metals.