Calibration of an <i>in-situ</i> fluorescence-based sensor platform for reliable BOD5 measurement in wastewater

Abstract Reliance on biochemical oxygen demand (BOD5) as an indicator of wastewater quality has hindered the development efficient process control due to associated uncertainty and lag-times. Surrogate measurements have been proposed, with fluorescence spectroscopy a promising technique. Yet, assessment in-situ sensors across multiple treatment plants (WwTPs), at different stages, is limited. In this study multi-parameter sonde (two peaks, turbidity, temperature electrical conductivity) was used provide BOD5 surrogate measurement. The deployed three WwTPs, post primary settlement tanks (PST) final effluent (FE). Triplicate laboratory BOD5, from independent laboratories were calibrate sensor, high variability apparent for FE samples. Site specific sensor calibrations yielded best results (R2cv = 0.76–0.86; 10-fold cross-validation) mean improved calibration. When combining PST sites reasonable calibration still achieved 0.67) suggesting transfer between WwTPs may be possible. This highlights potential use online optical robust surrogates in WwTPs. However, careful (i.e. replicated measurements) required can uncertainty.