Abstract
Improvements in the application of ionizing radiation for the conditioning of sewage sludges are facilitated by knowledge of the governing processes. Accordingly, a model based on radiation chemical principles was developed and verified experimentally. Results of steady state irradiation and pulse radiolysis experiments, utilizing a variety of radical scavengers, demonstrated that the improvement of the dewatering and sedimentation characteristics of some sludges by gamma irradiation was produced mainly by the actions of the oxidizing OH radical on the suspended solids. The liquid and solid phases compete for OH as shown by the fact that the extent of conditioning of anaerobically digested sludge by gamma irradiation was inversely proportional to the “scavenging power”, namely, the product of the bimolecular rate constant for OH and the concentration of a given scavenger. The irradiation effect was modified to the identical extent, within experimental error, for the same value of the scavenging power, regardless of the particular scavenger employed. The attack of the OH radical on the organic solids produced, as anticipated, an increase in the concentration of organic compounds in the liquid phase. Pulse radiolysis experiments, utilizing competition between CNS − and OH, demonstrated that the scavenging power of centrifugants of raw sludge was greater than that of anaerobically digested sludge. Results of steady state and pulse radiolysis experiments showed that the scavenging power of the suspended solids greatly exceeded that of liquid phase components. This work leads to recommendations for improvements in the design and operation of sludge irradiation facilities.
Published Version
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