A New Kinetic Model for Ultraviolet Disinfection of Greywater

Ultraviolet (UV) disinfection of greywater has a number of advantages for small scale applications, but the UV disinfection efficiency can be impeded by high levels of particulates and chemicals in the greywater, micro-organism aggregation, and the geometry between the UV lamp and surrounding sleeve leading to suboptimal flow paths through the lamp assembly. Most process models for UV systems are empirical in nature and do not adequately represent the distribution of UV dose that is actually delivered to micro-organisms in a continuous flow system. This paper presents a model which incorporates: (1) variations in micro-organism sensitivity to UV radiation, (2) the variation of dose received in the UV reactor chamber, and (3) the shielding effect of part of the micro-organism population by the presence of particulates. The model is capable of predicting the asymptotic decay observed in bacterial survival curves when organisms are exposed to a UV dose in a greywater matrix and has been calibrated using experimental data on a series of synthetic greywaters of differing composition and validated against a series of real greywater samples. The model compares favorably to other UV disinfection models and allows the influence of water quality parameters such as turbidity, suspended solids, and UV absorbance to be examined. This allows water quality limits to be defined beyond which the UV disinfection of greywater becomes ineffective. Acceptable performance criteria are established for low power UV systems for the treatment of greywater, which have implications for the selection of suitable annular UV reactors.