Mild temperature hydrothermal oxidation of anaerobic fermentation filtrate for carbon and nitrogen recovery in a regenerative life support system

Hydrothermal oxidation of fermentation filtrate was conducted in a tubular reactor to recover carbon (as CO2) and nitrogen (as NH4+ or NO3-) at mild temperature destined for use in a regenerative life support system. Temperature, residence time (t(R)), and the oxidizer equivalence ratio (OER) were the experimental variables in the oxidation tests. The highest carbon recovery achieved was 68.2%, with 80.1% of the total nitrogen being retained in the form of NH4+ or NO3- at 380 degrees C, t(R) = 48 s and OER = 4.0. The effect of temperature, residence time and OER on carbon and nitrogen distribution were discussed. Moreover, a first-order reaction rate was applied by means of regression analysis to estimate the carbon conversion rates. Prolonging the residence time at 380 degrees C with OER = 3.0 is proposed to be a promising modification to increase both carbon and nitrogen recovery from the filtrate.