Stability and response of bioreactor: An analysis with reference to microbial reduction of SO2

摘要

A continuous B. Braun fermenter undergoing the first stage of bioreduction of gaseous pollutant, SO2-abiotically transformed to sulfite solution, using Desulfotomaculum nigrificans, purchased from NCIM, Pune (India), has been analysed both under steady and dynamic states. The kinetics of the microbial growth have been observed to face product inhibition in the entire range of inlet sulfite concentration of 0.904-1.696 g/dm~3. The kinetic parameters like maximum specific growth rate (mu_m), saturation constant (K_s) and product inhibition constant (K_P) have been evaluated by non-linear regression analysis and their values have been found to be 0.185 ks~(-1), 6.512 x 10~(-3)g/dm~3 and 0.045 g/dm~3, respectively. The yield coefficient of generation of biomass with respect to the uptake of sulfite, Fx/s, has been observed to vary non-linearly with the fractional conversion of sulfite and the functional relationship has been determined as 1.918 exp(-1.984X_A). Under the present range of values of dilution rate (2.778 x 10~(-3) to 0.056 ks~(-1)), the steady state conversion of sulfite has been observed to lie in the range of 99.6-6.12%. Non-ideality, i.e., the extent of deviation from the ideal hydrodynamic behavior of the bioreactor has been assessed using a two-parameter model. The parameters of this model have been evaluated conducting step-type tracer experiments for residence time distribution (RTD) of inlet tracer molecules in the fermenter. The values of the non-ideal parameters indicate that the reactor behaves almost ideally under the present investigation. For a priori determination of the stable regime of operation of this biosystem, in general, global and local stability analyses have been done by the techniques of separatrices and linear analysis, respectively. The process dynamics and the control behavior of the system have been assessed by the analysis of its response with respect to step changes in the forcing functions, namely flow rate and the sulfite concentration in the inlet stream of the bioreactor.