Spectrophotometric determination of total carbohydrate (TCH) in the wastewater samples by anthrone reagent is a simple and rapid method to follow the utilization of substrate, and hence the reduction of BOD5 load during the biological treatment process with chemoheterotrophs. However, for the coloured wastewater samples or treatment plant effluents, a correction factor was found necessary to compensate the colour inferences. Studies were conducted on various waste sulfite liquors (NH3-, Ca-, Mg-, Mixed- and Na-WSL) which provide a wide range of colours from creamy to black. The correction factor was calculated from the deviation of the standard calibration curves of glucose with and without the presence of WSL. These correction factors depended both on the nature and on the amount of WSL present. Within the practical dilution range of various WSL for the determination of TCH (1:1,000 - 4:1,000 v/v), the correction factors varied from 15 to 40%, which is highly significant if the correction was not made. In all WSL samples, the correction factor became more significant at higher concentration of WSL in the solution. Spectrophotometric studies of WSL at various concentrations within the visible range led to the development of the following empirical equation expressing their colour,  
$$\Lambda = \Lambda _{\rm s}\left( {1 + {[D_{\rm c}/D]}^2} \right)^{{\rm n/2}}$$

where Λ, Λs, Dc, D and n are the maximum transmitted wavelength of WSL solution, the maximum transmitted wavelength of water (solvent), the critical dilution of WSL, the dilution of WSL (reciprocal concentration of colouring materials) and the chromatic index of WSL respectively.

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