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The threat to public health is immense when wastewater is not adequately disinfected before being irrigated, exposing people to infectious diseases. Chlorine dioxide is known to be effective against protozoans. It also does not form trihalomethanes (THMs) that are carcinogenic and encountered when chlorine is used as a disinfectant. Chlorine dioxide has not been used for disinfecting wastewater because of problems encountered in accurate determination of chlorine dioxide residues. Its use has been limited to drinking water. Measurement of chlorine dioxide is problematic due to interferences from suspended solids and color in wastewater. The objectives of present studies were to measure chlorine dioxide residuals in wastewater spectrophotometrically using Lissamine Green B (LGB). Care must be taken in obtaining LGB and for these experiments I used LGB obtained from Sigma Aldrich. This dye procured from different manufacturer gave different results. Dry media chlorine dioxide was used to generate ClO2 solution on-site. Demand studies were done on different kinds of wastewater to study the chlorine dioxide demand pattern. Chlorine dioxide in wastewater was estimated by LGB method which is pH sensitive and thus pH must be maintained to get reproducible and reliable results. This method was found to be effective at measuring ClO2 residuals from 3 to 0.1 mg/L concentration range.