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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.

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The present communication reports experimental and modelling work pertaining to the independent roles of pH and temperature on deactivation of a crude lipase from Mucor juvunicus. Experimental data of lipolytic activities were generated by a classic pH-stat assay on a triolein emulsion following incubation at several pH values for a fixed time, or at several temperatures for various times; postulated models were then fitted by nonlinear fitting to such data. The pH-dependence data were best fit by assumption of three forms of enzyme with increasing states of protonation, with pK, values of 6.2 and 11.3, respectively, where only the intermediate form is stable within the time frame considered. The thermal-dependence data were best fit by assumption of parallel steps of deactivation and rearrangement, with activation energies of 228.8 and 221.7 kl mol-I, respectively.

A flow injection multisite detection system was developed for correction of the sample blank in a colorimetric determination. By using detector relocation, a single spectrophotometer is used for the sequential reading of the sample blank and of the colored product; the sample crosses the flow cell to measure intrinsic absorption, the color reagent is subsequently added, and the flow cell is relocated to provide the reading of the resulting plug. The subsequent detector relocation immediately after peak maximum increases the determination frequency. This strategy was tested in the colorimetric determination of iron in soil samples based on the reaction of Fe (II) with 1,10-phenanthroline after reduction of Fe (III) to Fe (II) by ascorbic acid. The results obtained for 15 soil extracts were in good agreement with those obtained by the reference procedure. Relative standard deviations better than 4% were obtained, with a sampling rate of 30/h.