Evaluation of electroactive denitrifiers at different potentials, temperatures and buffers based on microcalorimetry

Electroactive denitrifiers contribute to the nitrate removal in a bioelectrochemical system, but their metabolism and growth parameters remain vague. In this study, microcalorimetry as a suitable method was used to evaluate the metabolism and growth parameters of electroactive denitrifiers at different cathode potentials, temperatures and buffer solutions. The suitable cathode potential and temperature for electroactive denitrifiers were deemed as -100 mV and 30 °C, respectively. The suitable buffer was found to be phosphate buffer solution but can be replaced by bicarbonate buffer solution. When cultivated with bicarbonate buffer solution at -100 mV and 30 °C, electroactive denitrifiers achieved a specific nitrate removal rate of 2.20 ± 0.08 × 10^-10 mg NO₃^--N·(min·cell)^-1 and two growth rate constants (k₁ = 0.0051 ± 0.0004 min^-1, k₂ = 0.0030 ± 0.0004 min^-1), with gaseous nitrogen as the end product. The bioelectrochemical denitrification behaved as a two-step process, in which the nitrite reduction to gaseous nitrogen was the rate-limiting step.