Absorbance Based Model for Determination of Biochemical Oxygen Demand

Aims: The paper presents the development of mathematical model for the spectrophotometric determination of BOD along with its validation and an illustrative example of its application for sewage water treatment plant.
Place and Duration of Study: The concept of determination of BOD using spectrophotometric absorbance and mathematical modeling of absorbance to measure BOD was developed at the Department of Chemistry and Department of Electrical Engineering J. N. V University, Jodhpur.
Methodology: The wavelength of 440 nm, selected from the linear zone of response spectrum has been used as the base for measuring absorbance. The performance of the proposed spectrophotometric method is assessed by repeated measurement of DO for standard glucose-glutamic acid (GGA) solution and its comparison with DO values obtained by Winkler’s titrimetric method. Mathematical models of different orders were developed and analyzed for goodness of fit. A linear model was found to be the best in order to obtain the DO values whereas a quadratic model found to be suitable for the estimation of BOD.
Results: The results depict a good correlation in the variation of absorbance values with DO values obtained from Winkler’s titrimetric method. Application of the proposed method for the measurement of biochemical oxygen demand (BOD) in waste water samples acquired from the solid waste treatment plant has been included as an illustrative example.
Conclusion: The quadratic model has been found to be the best model for estimating the depletion of DO after incubation in terms of change in absorbance from day 1 and day 5 for BOD modelling on the basis of analysis of SSE, RMSE, R-square and the polynomial coefficient of the model. The major advantage of the proposed approach is that the results do not depend on the identification of single end point and observer subjectivity.