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This paper reports on a new method for rapid determination of organic matter (OM) in soil and municipal sludge samples, based on a redox reaction (i.e., conversion of OM into CO2 by dichromate), involving the headspace gas chromatographic technique (HS-GC). For the soil samples (with a lower OM content), the sample reaction was conducted in a sealed headspace vial under the given conditions (135 °C for 20 min) and the CO2 from the reaction is directly measured by HS-GC. For the municipal sludge samples (i.e., with a higher OM content), the sample reaction was conducted in an open vial under the above conditions. Then, a portion of the reaction medium was taken and added into a sealed vial containing an excess amount of oxalic acid, followed by HS-GC measurement, from which the residual amount of potassium dichromate in the reaction medium can be determined and thus the OM content in the sample can be calculated. The results showed that the present method has good reproducibility and accuracy, with a relative standard deviation < 5% and recovery between 91.8% and 106%. Based on a headspace auto-sampler, high-throughput determination of the OM content for batch sample analysis can be realized.

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 (K2Cr2O7) based on the production of trivalent chromium ions (Cr3+). Cr3+ could be determined by subtracting the absorption at 800 nm (spectral interference) from the absorption at 650 nm (only contributed by Cr3+). 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.

This article reported a new headspace gas chromatography (HS-GC) for the determination of hexavalent chromium Cr(VI) in solid waste hypochlorite treated leachates. The method was based on the reaction between Cr(VI) and an excess potassium hydrogen oxalate in a pH buffer solution in the headspace vial at 60℃, followed by HS-GC measuring the carbon dioxide produced. To eliminate the interference from hypochlorite in the leachates, two reaction times, i.e., 6 and 7 min, were selected. At pH = 1.50, it was found that the reaction of oxalate with Cr(VI) was partly achieved in 6 min and fully achieved in 7 min, and the reaction of oxalate with hypochlorite was achieved in 6 min. Based on two separate HS-GC measurement on the CO2 signals at 6 and 7, respectively, the amount of Cr(VI) in the sample can be calculated. The results showed that the present method has a good measurement precision (RSD

This paper describes a headspace gas chromatographic (HS–GC) method for the in-situ determination of the observed yield coefficient (Yobs) of aerobic activated sludge from domestic wastewater treatment plants. It is based on the measurement of oxygen and carbon dioxide in samples that have been incubated in headspace vials for relatively short periods of time. The method has good precision (the relative standard deviation