Abstract
Real-time bioprocess monitoring is crucial for efficient operation and effective bioprocess control. Aiming to develop an online monitoring strategy for facilitating optimization, fault detection and decision-making during wastewater treatment in a photo-biological nutrient removal (photo-BNR) process, this study investigated the application of Raman spectroscopy for the quantification of total organic content (TOC), volatile fatty acids (VFAs), carbon dioxide (CO2), ammonia (NH3), nitrate (NO3), phosphate (PO4), total phosphorus (total P), polyhydroxyalkanoates (PHAs), total carbohydrates, total and volatile suspended solids (TSSs and VSSs, respectively). Specifically, partial least squares (PLS) regression models were developed to predict these parameters based on Raman spectra, and evaluated based on a full cross-validation. Through the optimization of spectral pre-processing, Raman shift regions and latent variables, 8 out of the 11 parameters that were investigated—namely TOC, VFAs, CO2, NO3, total P, PHAs, TSSs and VSSs—could be predicted with good quality by the respective Raman-based PLS calibration models, as shown by the high coefficient of determination (R2 > 90.0%) and residual prediction deviation (RPD > 5.0), and relatively low root mean square error of cross-validation. This study showed for the first time the high potential of Raman spectroscopy for the online monitoring of TOC, VFAs, CO2, NO3, total P, PHAs, TSSs and VSSs in a photo-BNR reactor.
Highlights
Demographic expansion and the improvement of standards of living around the world have led to rapid urbanization, intensive agricultural practices and industrial expansion
The models developed for each parameter were evaluated mostly based on the root mean square error of cross-validation (RMSECV) and R2CV, while still considering the calibration parameters, i.e., the root mean square error of calibration (RMSEC) and the coefficient of determination of calibration (R2Cal)
This study showed that Raman spectroscopy, allied with partial least squares (PLS), is a very promising tool for monitoring the concentrations of total organic content (TOC), volatile fatty acids (VFAs), CO2, NO3, total phosphorus (total P), PHAs, total suspended solids (TSSs) and volatile suspended solids (VSSs) in a photo-Biological nutrient removal (BNR) reactor in real-time
Summary
Demographic expansion and the improvement of standards of living around the world have led to rapid urbanization, intensive agricultural practices and industrial expansion. Environmental and water pollution increased, either through the release of waste streams with high concentrations of carbon, nitrogen (N) and/or phosphorus (P), or through the excessive use of fertilizers [1]. Biological nutrient removal (BNR) is the most common process implemented for simultaneous P and N removal, typically through sequential zones in activated sludge systems: anaerobic for carbon uptake and P release; anoxic for heterotrophic denitrification and P uptake; and aerobic for nitrification and P uptake. Such BNR systems require intensive O2 supply, often accounting for approximately 60% of WWTPs energy costs [4,5]
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