SYNOPSISThe thermal degradation of poly (N-vinyl-2-pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200-600°C under nitrogen and oxygen atmospheres a t various heating rates. The apparent activation energy of the degradative process was determined by the application of kinetic treatments, giving an average value of 242 kj/mol in Nz, whereas in the presence of oxygen, two trends may be considered At relatively low temperatures (200-400°C) and degrees of conversion, a, lower than 0.5, we obtained an average value of 199 kjlmol, whereas in the temperature interval 400-600°C with degrees of conversion higher than 0.5, the value of E, was 306 kjlmol. Isothermal experiments carried out in N2 in the interval 350-400°C gave an average value of E. = 231 kj/mol, in good agreement with that obtained from dynamic treatments. The FTIR spectra of the volatile compounds evolved in degradation experiments carried out in Nz as well as in the presence of oxygen suggest that PVP is thermally degraded, predominantly, by the release of the pyrrolidone side group and the subsequent decomposition of polyenic sequences. 0 1993 John Wiley & Sons, Inc.

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The aim of this study was to investigate the feasibility of a bioreactor system and its scale-up to remove Cr(VI) from solution. The bioreactor is based on an innovative process that combines bioreduction of Cr(VI) to Cr(III) by the bacterium Arthrobacter viscosus and Cr(III) sorption by a specific zeolite. Batch studies were conducted in a laboratory-scale bioreactor, taking into account different operating conditions. Several variables, such as biomass concentration, pH and zeolite pre-treatment, were evaluated to increase removal efficiency. The obtained results suggest that the Cr removal efficiency is improved when the initial biomass concentration is approximately 5 g L -1 and the pH in the system is maintained at an acidic level. Under the optimised conditions, approximately 100 % of the Cr(VI) was removed. The scale-up of the developed biofilm process operating under the optimised conditions was satisfactorily tested in a 150-L bioreactor.

Optimum conditions suggested by the second-order polynomial regression model for attaining maximum decolorization were dye concentration 4.83 mg/L, electrode surface area 15 cm(2), voltage 14.19 V, and treatment time of 34.58 min.