Bioscrubbing of waste gas-substrate absorber to avoid instability induced by inhibition kinetics

The stability of a continuous stirred tank bioreactor treating a gas stream containing monochlorobenzene (MCB) was studied theoretically and experimentally. A bioreactor inoculated with Pseudomonas sp. strain JS150 was submitted to successive step disturbances in the MCB load, inducing washout and system instability. With time, and subject to high MCB concentrations in the biomedium, the microorganisms appeared to adapt to high MCB load, and needed increasingly severe shocks to induce washout. To improve the bioreactor stability, the influence of an MCB-absorber prior to the bioreactor was investigated, using silicone oil as the absorbent for MCB. A parallel was established with the first set of experiments (no absorber). Phase plane plots showed how the presence of the absorber changed the system trajectories from washout into stable pseudo-steady states. Experimental results confirmed the benefits of the absorber in avoiding washout under high MCB loads. At periods of low loading, MCB was desorbed from the absorber. For the same loading conditions, removal efficiencies were much higher than when no absorber was present. Elimination capacities observed in the bioreactor were much higher than those previously reported for biotrickling filters treating MCB containing gas streams: 300 to 450 g m(-3) h(-1). Gas inlet concentrations were in the range 12 to 65 g m(-3), well above the 5 g m(-3) upper limit usually suggested for biological treatment of waste gases, showing that highly concentrated gas streams may be biologically treated so long as inhibitory concentrations are not reached in the bioreactor.