Estimating The Kinetics And Stoichiometry Of Heterotrophic Denitrifying Bacteria With Glycerol As An External Carbon Source

Abstract

Wastewater treatment facilities in the Chesapeake Bay watershed are focusing their attention on nitrogen removal to meet future effluent limitations of about 3-4 mg N/L. External carbon is added during denitrification to facilitate the removal of nitrate. This study investigates the kinetics and stoichiometry of glycerol as an external carbon source for denitrification. Biodiesel-based glycerol acclimated mixed liquor was fed glycerol as an external carbon source in lab scale batch experiments to estimate specific denitrification rate (SDNR), maximum specific growth rate, C:N ratio, growth yield and half saturation constants for COD limiting conditions. The average SDNR for acclimated and unacclimated mixed liquor was 1.4 mg NO x -N /gVSS/hr. The maximum specific growth rate was estimated at 3.4 d -1 . Stoichiometric C:N ratio and growth yield were estimated as 4.2 mg COD/mg NO x -N and 0.32 mg biomass COD/mg NO x -N respectively. The half saturation constant was estimated between 5-8 mg COD/L.

Glycerol-driven Denitratation: Process Kinetics, Microbial Ecology, and Operational Controls

“…The influent COD:NO3 --N ratio required for glycerol-driven denitrification (NO3 --N to N2 reduction) was thermodynamically 30 determined to be 5.9:1 (see SI). This corresponded well with experimentally-determined operational ratios of 4.2:1 to 5.6:1, 16,20,31 although the lowest reported ratio 16 may not be fully representative as it was determined via ex situ batch assays as opposed to steady-state continuous flow bioreactor or SBR operation. Stoichiometric analysis revealed that influent COD:NO3 --N=2.4:1 (see SI) would provide only enough electrons via COD oxidation to reduce NO3to NO2on a theoretical electron equivalence basis as opposed to full denitrification.…”

“…Several water resource recovery facilities are switching to glycerol due to the operational and safety risks associated with methanol. 12 Glycerol is similar in cost to methanol and less expensive than ethanol and acetate, [16][17][18] is available as a waste or byproduct, 19,20 and has no known inhibitory effects on the anammox process, unlike methanol. 21 NO2accumulation during glycerol supplementation was also anecdotally observed in full-scale treatment plants resulting in unintentional enrichment of anammox on the produced NO2 -.…”

Glycerol-driven denitratation: process kinetics, microbial ecology, and operational controls

“…Several water resource recovery facilities are switching to glycerol due to the operational and safety risks associated with methanol. 14 Glycerol is similar in cost to methanol and less expensive than ethanol and acetate, 18–20 is available as a waste or byproduct, 21,22 and has no known inhibitory effects on the anammox process, unlike methanol. 23 NO 2 − accumulation during glycerol supplementation was also anecdotally observed in full-scale treatment plants resulting in unintentional enrichment of anammox on the produced NO 2 − .…”

Cassava stillage and its anaerobic fermentation liquid as external carbon sources in biological nutrient removal

“…Similar values were obtained with dairy effluent, glycerin and meat processing wastewater. Some other studies, for instance, with glycerol, fusel oil, brewery effluent, and wine distillery effluent revealed values exceeding 13 mg N/(g VSSh) (Monteith et al, 1980;Bernet et al, 1996;Hinojosa et al, 2008;Kampas et al, 2009).…”