Simple and efficient dual-wavelength spectroscopy for the determination of organic matter in sewage sludge from wastewater treatment.

In this study, a dual-wavelength spectroscopic method for rapid determination of organic matter in sludge was developed. The contents of the organic matter were calculated by determining the consumption of potassium dichromate (K 2 Cr 2 O 7 ) based on the production of trivalent chromium ions (Cr 3+ ). Cr 3+ could be determined by subtracting the absorption at 800 nm (spectral interference) from the absorption at 650 nm (only contributed by Cr 3+ ). The results showed that the relative standard deviation in the test was less than 5%. The same set of samples was used and when the content of organic matter was more than 150 g kg -1 , the relative difference between the spectroscopic method and titration method was within 1%. Furthermore, the method does not require calibration based on the standard samples. In conclusion, the present method is simple, reliable, accurate and suitable for application in mass testing for sludge samples.