Rapid and pollution-free characterization of intracellular polyphosphate and orthophosphate using mid-infrared spectroscopy combined with chemometrics in the denitrifying phosphorus removal process

Abstract

To rapidly characterize the content of intracellular polyphosphate (Poly-P) in the denitrifying phosphorus removal process, the conversion of the intracellular Poly-P was analysed with mid-infrared spectroscopy. A quick determination model (PLS model) for the content of the intracellular Poly-P was established with mid-infrared spectroscopy and the chemometrics of the partial least squares (PLS) method. Additionally, the correlation between Poly-P variation and orthophosphate variation was analyzed. Principle component analysis was used as a spectral pre-processing method, with 5 being the optimal number of principle component. A PLS model was established, via partial least squares method, between the absorption data and the content of the intracellular Poly-P. The PLS model of the content of the intracellular Poly-P showed that the correlation coefficient was 0.9784 between the actual value and the calibration value, and the root mean square error was 0.0215. The test results of the PLS model showed that the correlation coefficient was 0.9602 between the actual value and the prediction value, and the root mean square error was 0.0398. In addition, the correlation between Poly-P variation and the orthophosphate variation was established, with the coefficient being 0.9449. The result shows that the content of intracellular Poly-P can be determined accurately when the content is 1.28–5.71% by mid-infrared spectroscopy coupled with PLS method. Additionally, the removal effect of the orthophosphate may be predicted rapidly in the denitrifying phosphorus removal process. The proposed method is demonstrated to be pollution-free and more rapid compared with other approaches measuring the content of the intracellular Poly-P and orthophosphate variation.