Efficacy of Alkaline Hydrolysis as an Alternative Method for Treatment and Disposal of Infectious Animal Waste

The efficacy of alkaline hydrolysis as an alternative for incineration or autoclaving during treatment and disposal of infectious waste was evaluated by testing for the destruction of samples of pure cultures of selected infectious microorganisms during digestion of 114 to 136-kg loads of animal carcasses in an animal tissue digestor at the Albany Medical College. Ten milliliter samples of pure cultures of each microorganism were divided among 3 dialysis bags made from narrow diameter dialysis tubing, and each of these bags was placed inside another dialysis bag made from larger diameter dialysis tubing. Each double-bagged sample was suspended from the cover of the carcass basket of the tissue digestor so that it was completely covered by hot alkaline digestion solution during the carcass digestion process. The following organisms were required by the New York State Department of Health as representative pathogens for testing sterilization capabilities of the procedure: Staphylococcus aureus, Mycobacterium fortuitum, Candida albicans, Bacillus subtilis, Pseudomonas aeruginosa, Aspergillus fumigatus, Mycobacterium bovis BCG, MS-2 bacteriophage, and Giardia muris. Animal carcasses included pigs, sheep, rabbits, dogs, rats, mice, and guinea pigs. The tissue digestor was operated at 110 to 120 C and approximately 15 lb/in2 (gauge) for 18 h before the system was allowed to cool to 50 C and dialysis bags were retrieved and submitted for microbial culture. None of the samples obtained from the dialysis bags after the digestion process yielded indicator bacteria or yeast. Giardia cysts were completely destroyed; only small fragments of what appeared to be cyst wall could be recognized with light microscopic examination. No plaque-forming units were detected with MS-2 bacteriophage after digestion. Samples of the hydrolyzate also did not yield growth on culture media. Animal carcasses were completely solubilized and digested, with only the inorganic components of the bones and teeth remaining after draining and rinsing of the digestion vessel. Alkaline hydrolysis, as performed in this tissue digestor, completely destroyed all representative classes of potentially infectious agents as well as disposing of animal carcasses by solubilization and digestion.