Research output: Contribution to journalArticlepeer-review


In the sterilization of those Health Care Waste that are marked as possibly infectious, microwaves (MW) have long been proposed as an alternative means to steam. The effectiveness of the operation is assessed determining the fraction that has survived to the sterilizing agent of a known starting population of micro-organisms. Customarily, this population is introduced into the waste mass in the form of one or more sealed vials. These make up an artificial environment which is completely under control; but onto it the sterilizing agent could a priori behave with higher or lower effectiveness, compared with the loose mass which is directly exposed to it. As far as the traditional steam sterilization has been the only process available, the meaning and representativeness of the micro-organisms’ response in sealed vials have not been questioned. In principle, however, a penetrative physical sterilizing agent – as MWs are – could sterilize a standard vial’s content better than would do steam, which will just flow around it. If an operator is about deciding whether to shift to MWs, this success induces him to reduce the energy to feed to the waste mass, compared to that he deemed satisfactory before, when transferred by steam. Since the onset of MW sterilization technique, therefore, a need for validation in the most realistic conditions arose. This demand drives researchers to work out techniques for bacterial count that have no barriers: that is, techniques that count the same tracing cells, but after they, 1) have been freely dispersed in the whole mass; 2) have undergone the same disinfecting actions as the surrounding mass; 3) have been sampled from the mass at the end of the process. It is evident that – in order to gain certainties in phase 2 – two severe uncertainties have been unwillingly introduced as phases 1 and 3. Indeed, the experimental campaign on which this paper reports was aimed at simulating at lab scale the MW sterilization of synthetic waste samples which had been contaminated with known amounts of spores; to get quantitative information on the efficiency and identify the possibly critical steps of the whole procedure. In the 6 different sessions that were run, the operational variables were the waste moisture content (25% – 80%) and the amount of energy supplied as MW; residence time 40 min instead was common to all tests. The temperature patterns were recorded, and at the end the whole mass was washed to detach the spores for following cultivation – count. In this way the critical features of the procedure were identified and ranked by severity. It was foreseen that the procedure would be time-consuming and would require handling of considerable amounts of water and glassware. The experiments showed something more serious: actually, the physiological solution alone – without any surfactant agent added – is unable to detach quantitatively the spores from the waste chips and the beaker walls. Addition of a few drops of surfactants – as was done by Oliveira et al. (2010) – is thus a technical detail which is critical for the success of the whole treatment – analysis chain. Of course we ought to have the certainty that the surfactant chosen does not interfere with the growing medium and / or the bacterial viability in the plate cultivation following. The loss of viable spores in washing the waste batches was calculated by us: 1) sampling and cultivating 1 ml wash solution coming from the control sample inoculated and not irradiated (called K+); and then, 2) comparing the result with the known inoculum. Regrettably, less
Original languageItalian
Pages (from-to)71-86
Number of pages16
Volume5 n.2/2018
Publication statusPublished - 2018

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