UV DISINFECTION MODELING: IMPLICATIONS OF BACTERIAL COLONIZATION OF WASTEWATER SOLIDS

Fractions of fecal coliform based on the size of their associated particles were generated by sequential filtration of municipal wastewater. Size fractionation provided opportunities for modeling disinfection. The Scheible model for relating the non-inactivated bacterial density with total suspended solids (TSS) was modified. A weak correlation was found between the large fraction initial coliform concentration (operationally defined as organisms retained on a 20 μm filter) and TSS. The empirical WERF model appeared to describe the disinfection data well, with dose and initial fecal coliform concentration as the most significant factors. The disinfection curves could be reconstructed successfully by a weighted addition of the disinfection characteristics of the fractions. The reconstruction was successful even when the initial fecal coliform concentrations of the size fractions was estimated by TSS. Reconstruction of the tail, along with the disinfection curve for the large fraction, indicated that about 1% of the organisms retained on a 20 μm filter contributed to the tail. Two other observations (the dependence of the disinfection rate constant for a fraction on the initial fecal coliform concentration of the fraction and that the whole sample survivor density approaches the large fraction survivor density at large doses) were described by the rational model (where the rate of disinfection is proportional to the survivor concentration raised to a power).