Testimonials
“We have found the performance of the system to be quite satisfying and user friendly. We are currently running low level O2 uptake experiments and are impressed with the sensitivity of the instrument.”
“I have found the performance of the Challenge AER-200 to be unmatched. The precise measurement of oxygen consumption, homogenous mass transfer of test materials, and constant and consistent operating temperature have enabled me to obtain extremely accurate test results, particularly as compared to other respirometer systems. I find the Challenge system to be extremely user friendly.”
Monitoring Denitrification Reactions
Nitrogen gas produced during denitrification reactions can be measured using the Challenge AER-200 respirometer system. In this case, the test culture is placed in a respirometer vessel with nitrate and organic electron donor. Carbon dioxide is scrubbed from the headspace using a caustic scrubber in the same manner used with aerobic oxygen uptake tests. Example test data are shown in the figure below when using COD/N ratio as a test variable (Cheng, 2000). The total nitrogen production increased with COD/N ratio up to around 4:1, which is approximately the theoretically required ratio. However, the reaction was completed sooner at higher COD/N ratios. The rate of nitrogen production an be determined as follows:
where 0.86 = liters of nitrogen gas per gram of nitrate nitrogen reduced at 20oC, YN = fraction of the nitrate nitrogen used for synthesis (YN Å 0.05 g N synthesized/g N oxidized), and RN = nitrate loading rate, g NO3–N/L–hr. When the system is operated under kinetically saturated nitrate conditions, RN2 is aximum and the active denitrifying biomass concentration, XaDn, can be estimated as follows:
where qmax–Dn is the maximum specific substrate conversion rate for denitrification reactions and averages 0.153 L N2/g XaDn/hr (0.5 g COD/g XaDn/hr) when using readily biodegradable substrates such as methanol, acetate, or glucose. The active denitrifying biomass for the example case was then 28 mg/L.