USING NITROGEN RATIO AS AN INDICATOR OF BIOMASS RETENTION AND STEADY-STATE IN ANAEROBIC FERMENTATION

ABSTRACT A relationship between the Nitrogen Ratio (NR) and the biomass retention and steady-state characteristics of anaerobic fermenters has been developed using data obtained from recent literature and a laboratory investigation. The study employed 25 L attached growth reactors (SPAG), a 300 L conventional flow through reactor (CSTR), and a 25 L upflow sludge blanket reactor (USB). Reactors were studied in replicate at hydraulic retention times (HRT) of 5, 3, 2, and 1 day. Fill ratios of 7.5%, 15%, and 30% were analyzed at all HRTs for the SPAG reactors utilizing two separate media types. Mesophillic temperatures (35° C) were maintained in all reactors. This study indicates that an NR of 1.00 + 5% should be maintained to assure steady-state conditions. Serious questions are raised concerning the validity of *steady-state' data reported in the literature.