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 (theta = 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/m3 x d, respectively, and maximum nitrification volumetric conversion rates exceeded 300 g/m3 x 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.