Long-term effect of zero-valent iron on one-stage partial nitritation and anammox

Partial nitritation and anammox (PN/A) is an energy- and carbon-saving process for nitrogen removal from organic deficient wastewater. However, the PN/A effluent often requires polishing to eliminate the nitrate produced by anammox. Iron as the essential element for living organisms has been tested for nitrate reduction and phosphorus recovery in wastewater treatment processes. Here, we proposed a novel process coupling PN/A with iron-based denitrification for efficiently removing nitrogen and phosphorus in a single reactor. Two laboratory-scale bioreactors were operated under oxygen-limited conditions in parallel. Fe-0 with a dosage of similar to 27 mg Fe/L-wastewater was continuously dosed in the experimental reactor, with the other serving as a control. Throughout 300 days of operation, the results showed that experimental system always had significantly high removal efficiencies of organic carbon, nitrogen and phosphorus compared with control system. The total nitrogen removal achieved 90.1 +/- 1.2 % at the rate of 0.96 +/- 0.03 kg N/(m(3)center dot d) due to the improved activity of ammonia oxidizers, anammox bacteria and denitrifiers and enriched nitrogen conversion pathway (i.e., ironbased autotrophic denitrification) with Fe-0 supplement. The total phosphorus removal was synchronously improved to 80.2 +/- 9.1 % mainly driven by the phosphate precipitation with iron. This study provides new insights into achieving high-level nitrogen and phosphorus removal in a single reactor, and deepens our understanding of the improved nutrients removal mechanism mediated by iron.

Automated summary

PN/A is an energy- and carbon-saving process for nitrogen removal from organic deficient wastewater. In this study, a novel process coupling PN/A with iron-based denitrification was proposed to efficiently remove nitrogen and phosphorus in a single reactor. The experimental results showed significantly high removal efficiencies of organic carbon, nitrogen, and phosphorus in the experimental system compared with the control system. The total nitrogen removal achieved 90.1% and the total phosphorus removal reached 80.2%.