Non-invasive estimation of biomass concentration in activated sludge wastewater treatment using laser speckle imaging technique

초록

Accurate biomass concentration measurement is essential for modelling and optimizing activated sludge processes in biological wastewater treatment. This study employs the laser speckle imaging (LSI) technique, typically used for biomedical perfusion monitoring, in the challenging environment of activated sludge. By quantifying the link between temporal speckle decorrelation and microbial kinetics, LSI was established as a novel soft-sensing framework for non-invasive biomass estimation in wastewater treatment. Quantitative relationships between LSI-derived speckle decorrelation indices and biomass concentrations were established by analyzing temporal autocorrelation related to biomass concentrations. The LSI-derived biomass estimates were subsequently integrated into conventional Monod biokinetic models, enabling indirect estimation of key parameters including maximum substrate utilization rate ( q max = 2.5 d⁻¹), half-saturation coefficient ( K S = 42 mg/L), yield coefficient ( Y = 0.38 g VSS/g BOD), and endogenous decay coefficient ( b = 0.05 d⁻¹). These values align well with conventional physicochemical analyses and literature ranges, confirming the feasibility of LSI as an optical biomass sensor for wastewater treatment. The findings demonstrate that LSI captures concentration-dependent optical scattering dynamics related to floc motion and structural characteristics that complement bulk measurements. As a calibration-based soft-sensing tool used alongside conventional methods, the LSI technique offers potential for enhanced monitoring of wastewater treatment systems under controlled conditions, with further validation required for diverse operational environments. © 2026 Elsevier Ltd.

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