Photomodification Processing of Biologically Recalcitrant Pollutants

Recalcitrant pollutants, such as pesticides, plastics, and ligninsulfonates, a product of paper manufacture, are of increasing concern because microorganisms are not able to break these down at desirable rates. With insufficient rates of breakdown, one can observe increasing accumulation of these materials in the environment. To aid microorganisms in metabolizing such materials, photolytic processes have been developed that show the potential of treating process streams, allowing more efficient microbial utilization. These systems can be envisioned for production of microbial protein and for the pretreatment of materials before release into natural environments. Photolysis efficiency is dependent on the wavelength of light used, with light in the ultraviolet range, from 180 to 210 nm being most effective. An active free-radical reacting reagent, such as oxygen, is required for efficient modification. After modification a substrate can be used in growth chambers for production of microbial protein or be treated in a lagoon system before release to a natural environment. Aspects of control and instrumentation, which should be considered in future large-scale use of such processes, are discussed.