Ultraviolet disinfection of marginal effluents: determining ultraviolet absorbance and subsequent estimation of ultraviolet intensity

The ultraviolet (UV) absorbance characteristics of effluents with a wide range of water quality were measured using direct and integrating sphere spectroscopy. The point source summation (PSS) method was used to estimate the effect of three UV absorbance measurement techniques (filtered direct, unfiltered direct, and unfiltered integrating sphere) on estimation of UV intensity in a UV reactor. Intensity values estimated from the PSS model were compared with direct intensity measurements made with a chemical actinometer. Use of the integrating sphere method for measuring the UV absorbance of the bulk wastewater was validated experimentally with UV absorbance coefficients derived from chemical actinometry. Absorbance coefficient values derived from direct spectroscopy were significantly different from the actinometrically derived absorbance coefficients. Particulates in wastewater both absorbed and scattered UV light, decreasing the overall available UV radiation for disinfection. As compared to the integrating sphere method, use of either filtered or unfiltered direct absorbance to determine the UV intensity with the PSS model provided an overestimate or underestimate of UV intensity, respectively. No significant differences were observed between the chemical actinometry and point source summation methods of estimating UV intensity after accounting for experimental differences.