Kinetics and physiological characteristics of autotrophic dentrification by denitrifying sulfur bacteria

To study the kinetics and physiology of autotrophic denitrifying sulfur bac teria, a steady-state anaerobic master culture reactor (MCR) was operated f or over six months under a semi-continuous mode and nitrate limiting condit ions using nutrient/mineral/buffer (NMB) medium containing thiosulfate and nitrate. Characteristics of the autotropic denitrifier were investigated th rough the cumulative gas production volume and rate, measured using an anae robic respirometer, and through the nitrate, nitrite, and sulfate concentra tions within the media. The bio-kinetic parameters were obtained based upon the Monod equation using mixed cultures in the MCR. Nonlinear regression a nalysis was employed using nitrate depletion and biomass production curves. Although this analysis did not yield exact biokinetic parameter estimates, the following ranges for the parameter values were obtained: mu (max)=0.12 -0.2 hr(-1); k=0.3-0.4 hr(-1); K-s=3-10mg/L; Y-NO3=0.4-0.5mg Biomass/mg NO3 --N. Inhibition of denitrification occurred when the concentrations of NO3- -N, and SO42- reached about 660mg/L and 2,000mg/L, respectively. The autotr ophic denitrifying sulfur bacteria were observed to be very sensitive to ni trite but relatively tolerant of nitrate, sulfate, and thiosulfate. Under m ixotrophic conditions, denitrification by these bacteria occurred autotroph ically; even with as high as 2 g COD, autotrophic denitrification was not s ignificantly affected. The optimal pH and temperature for autotrophic denit rification was about 6.5-7.5 and 33-35 degreesC, respectively.