Nitrification‐Denitrification Biological Treatment of a High‐Nitrogen Waste Stream for Water‐Reuse Applications

This research was conducted to evaluate the use of biological nitrification‐denitrification systems as pre‐processors for recycling wastewater to potable water in support of space exploration. A packed‐bed bioreactor and membrane‐aerated nitrification reactor were operated in series with a 10:1 recycle ratio over varying loading rates. The dissolved organic carbon (DOC) removal exceeded 80% for all loading rates (θ = 1 to 6.8 days), while total nitrogen removal generally increased with decreasing retention time, with a maximum removal of 55%. The degree of nitrification generally declined with decreasing retention time from a high of 80% to a low of 60%. Maximum DOC and total nitrogen volumetric removal rates exceeded 1000 and 800 g/m 3 · d, respectively, and maximum nitrification volumetric conversion rates exceeded 300 g/m 3 · d. At low hydraulic loading rates, the system was stoichiometrically limited, while kinetic limitations dominated at high hydraulic loading rates. Incomplete nitrification occurred at high loading rates, likely as a result of the high pH and large concentrations of ammonia.