Physical, Chemical and Biological Agents Impacting Disinfection in Residuals

The inactivation of pathogens in residuals can be achieved by exposure to various types of stressors – physical, chemical and biological. The physical stressors include temperature, cavitation and radioactive irradiation (gamma and beta). These processes may solublize the organics, break the cells apart, destroy DNA, and other critical subcellular structures. The most common physical parameter utilized is temperature. The chemical stressors are associated with alkaline agents (raising the pH and causing exothermic reactions), acidic agents (lowering the pH and causing exothermic reactions), oxidation and reduction agents (destroying organics and stabilization of uncharged disinfectants) and non-charged disinfectants (required to disinfect helminth eggs and bacterial spores). The influence of chemicals that can assist in disinfection by raising/lowering the pH, enhancing exothermal production of energy, oxidation or reduction reactions with the residuals and the application of non-charged disinfectants are addressed. The biological processes result in temperature increases greater than 52°C and the production of biocidal by-products such as organic acids, aldehydes and alcohols, which act as disinfectants. The biological processing assists the disinfection processing by autothermal biological activity (increasing the temperature), reduction of the degradable organics (reducing the shielding of pathogens) and production of biocidal agents in the degradation process (fermentation or anaerobic processing). The key to these agents is to optimize their use and thereby reduce the process costs substantially. Though the causative agents responsible for disinfection may be grouped into the three categories, most treatment processes do not rely on one type only, they are a combination of the agent types. The anaerobic digestion, composting, air drying and alkaline stabilization processes are effected by at least three to four of these stressors. Currently, there is a great deal of process development in this area, but until we understand how to integrate these factors and explain how the mechanisms work, there will be a lot of skepticism by both the public and regulatory agencies.