Investigation of the Benefits of Using Direct Steam Injection in Effluent Treatment Systems

Abstract

In high-containment facilities the treatment of biological waste is very important. Liquid waste from containment level 4 laboratories and containment level 3 laboratories which handle nonindigenous animal pathogens is collected and treated in effluent treatment vessels. These vessels decontaminate the effluent using indirect steam via a steam jacket to heat the liquid to a minimum of 121°C. In some containment facilities the effluent is decontaminated by using direct steam injection to heat the load to the decontamination set point. This method of injecting steam directly into the load has the potential of providing agitation and reducing the amount of time necessary to heat the load to the set point, thereby reducing the processing time and increasing system capacity.

To investigate the benefits of direct steam injection, one of the effluent treatment vessels was modified so that direct steam could be used to supplement the indirect heating of the effluent. After functional testing was conducted to ensure the proper operation of the steam injection, tests were conducted to determine the efficacy of decontamination. For these tests the liquid load was spiked with bacterial spores and samples were taken during the warm-up process as well as during the decontamination period to determine when inactivation of the spores was achieved. To date, very little data have been published on the efficacy of effluent treatment vessels or comparing different methods of heating in these vessels.

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