Modeling the inactivation of Staphylococcus aureus and Serratia marcescens in clinical solid waste using supercritical fluid carbon dioxide

The aim of the present study was to determine an effective sterilization method for safe handling and recycle-reuse of clinical solid waste materials. Supercritical fluid carbon dioxide (SC-CO2) was applied in the inactivation of gram positive Staphylococcus aureus (S. aureus) and gram negative Serratia marcencens (S. marcescens) in clinical solid waste. The colony forming activity of the bacteria was completely lost at pressures 10–40 MPa, temperatures 35–80 °C and treatment period between 5 and 120 min. An increase in pressure at constant temperature and vice versa with the increasing treatment time enhanced the SC-CO2 inactivation efficiency. The inactivation process was illustrated by the modified Gompertz equation. The SC-CO2 inactivation of bacteria was compared with the steam autoclaved bacteria. Regrowth of the bacteria was observed in the autoclaved sample while no re-growth was detected in the SC-CO2 treated clinical solid waste. Results from SEM image analysis, cellular protein and enzymatic activity of untreated, autoclaved and SC-CO2 treated S. marcescens and S. aureus cells confirmed that SC-CO2 is an effective sterilization method.