Enzyme diffusion and cellulose breakdown in the bioremediation of medical waste

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Virginia Tech


The disposal of infectious medical waste has become a major environmental concern. New disposal methods are currently being investigated; one of these is a bioremediation process which utilizes enzymes in a batch reactor to render the waste noninfectious. The success of this biological process depends on (among other things) two mechanisms: the diffusion of the disinfecting enzymes into small crevices within the waste stream and the breakdown of cellulose-derived material by cellulase enzymes.

It was found that the waste stream contained a variety of small crevices which could possibly contain pathogens. Circulation in these crevices was restricted by their small openings and one must rely on diffusion of enzymes to disinfect their interiors. Numerical models for the diffusion of enzymes within one-dimensional and re-entrant crevices were developed and a method for comparing various re-entrant crevices was presented. From these models a conservative method for determining approximate disinfection times for the crevices was described. It was determined from this conservative method that most crevices within the waste will either be disinfected during the process or shortly thereafter.

This biological process also utilizes cellulases to breakdown the paper within the waste stream. Small-scale simulated waste experiments were conducted with cellulases to determine the increase in maximum mixable solids concentration and the mass reduction of the waste due to cellulase activity. The addition of cellulases to the slurry more than doubled the waste concentration which could be agitated and reduced the agitator shaft power by as much as 50% when compared to the simulated waste tests with no cellulase.

Significant mass reduction was also observed with the addition of cellulases to the slurries. Small-scale breakdown experiments were conducted with and without cellulases using newsprint as the substrate. These experiments were performed to determine the influence of cellulose hydrolysis by cellulases on agitator power. A simple mathematical model was developed and presented which described this phenomenon.