Towards an online, high-frequency determination of the biochemical methane potential of sewage sludge

This study aimed to develop a rapid method for determining the biochemical methane potential (BMP) of centrifuged sludge using Three-Dimensional Excitation-Emission Matrix Fluorescence Spectroscopy (3D-EEM) analysis of sludge supernatant. Sixty wastewater sludge samples were collected from four different treatment plants, spanning different treatment stages. The sludge supernatant, obtained from the centrifuge step in WWTP, underwent 3D-EEM analysis, revealing six characteristic components of dissolved organic matter via Parallel Factor Analysis (PARAFAC). Since the PARAFAC methodology is not easily available for online monitoring, a peak-picking technique by extracting fluorescence intensity at the maximum excitation-emission localization of the PARAFAC components has been used to obtain the explanatory variables chosen for BMP prediction.

BMP predictive models were established using explanatory variables from 3D-EEM analysis including fluorescence intensities at six excitation-emission wavelength pairs and 15 ratios derived from these intensities. Partial least squares regression was used for the predictive model calibration and highly accurate models for BMP prediction were obtained (R²v = 0.84, RPD = 2.59).

Significant progress was achieved as sample preparation for 3D fluorescence spectroscopy simplified to filtration and dilution, enabling rapid analysis within an hour. The possibility of integrating these steps into real-time analysis using a fluorescence probe suggests a pathway to online, high-frequency, and real-time determination of sludge BMP. This approach marks a substantial improvement over conventional BMP tests, which take weeks, and near-infrared spectroscopy, which requires sludge drying, taking several days for analysis. The study facilitates efficient and timely evaluation of the biochemical methane potential of sewage sludge.