A reveiw of recent experiments on the particle-association of fecal coliforms in wastewater effluents and the effect that this has on UV disinfection is presented. The most significant finding is that a direct linear correlation was observed between the total number of particles with associated coliform bacteria and the residual coliform bacteria concentration after UV disinfection. In contrast to the other treatment systems, effluents from an aerated and a facultative pond system had very low numbers of particles with associated coliforms. Therefore, despite high suspended solids concentrations, the pond effluents were easily disinfected with UV because the majority of the coliforms were not associated with particles. More research is needed, in particular, on the effect of UV irradiation on algal solids and the implications for the discharge or reuse of pond effluents. The main factors affecting the costs of UV compared to chlorine disinfection are also discussed.

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