Optimization of H2O2 action in sewage-sludge microwave digestion using Delta pressure vs. temperature and pressure vs. time graphs

In a previous study (Microchem. J. 59 (1998) 246-257) a systematic approach had been developed to optimize the experimental conditions applied during microwave-assisted mineralization of sewage-sludge samples. An innovative e laboration of data acquired by real-time monitoring of temperature and pres sure inside a closed vessel heated by microwave radiation had been performe d to determine thermodynamic and kinetic behavior of sample-HNO3 mixtures. The difference (Delta pressure) between the pressure recorded during sample -HNO3 heating and the corresponding vapor pressure of the pure reagent had been calculated as a function of temperature. Only concentrated HNO3 had be en chosen as a digesting reagent to reduce the complexity of the observatio ns to a single power-absorbing component. In this work the performance of o ther digesting reagents prepared by mixing HNO3 with H2O2 was tested. Resul ts obtained by examining Delta pressure vs. temperature graphs were compare d with treatment efficiencies determined by measuring total-organic-carbon variation as well as heavy-metal recovery in the digests. (C) 2000 Elsevier Science B.V. All rights reserved.