Dynamic mathematical models for biodegradation of formaldehyde by Ralstonia eutropha in a batch bioreactor

• Ralstonia eutropha degraded formaldehyde (HCOH) in a batch reactor.
• Experimental data of HCHO degradation was described well by the Luong kinetic model.
• The maintenance energy concept was applied to explain the growth yield variation.

Degradation of formaldehyde by Ralstonia eutropha was studied in a batch bioreactor operated in recycling mode (30 °C, initial pH of 6.5, aeration rate 0.5 vvm, and a recycling flow rate of 6 mL min−1). Growth kinetics equations were described using four substrate inhibition models, and the initial formaldehyde concentration ranged from 54.5 to 993.0 mg L−1. In each case, model parameters were estimated interactively using nonlinear regression analysis and on the basis of the goodness of fit, the fitness of the model to the experimental data was obtained (i.e., the coefficient of determination and the percent of standard deviation). The estimated parameters according to the Luong equation were μmax = 0.101 h−1, KS = 54.1 mg L−1, Sm = 1329 mg L−1, and n = 2.07. According to the maintenance energies explained by Pirt, cell maintenance was quantified with q = Aμ + B; where A and B are the associated and non-associated growth parts of substrate consumption, respectively. The importance of these terms was verified using the developed models, which would efficiently describe the dynamic nature of growth and formaldehyde biodegradation.