Tracking performance and disturbance in decentralized wastewater treatment systems with fluorescence spectroscopy†

Abstract

Fluorescence spectroscopy holds promise as a rapid tracer of performance in decentralized wastewater treatment systems (DEWATS) that may reduce the monitoring burden on communities. In this study, we examined changes in chemical oxygen demand (COD), fluorescence-based indices, and parallel factor analysis (PARAFAC) modeled components under normal operation and during periods of disturbance at the time of scum removal in real decentralized treatment settings and in laboratory simulated wastewater treatment with an anaerobic baffled reactor (ABR). Amino acid-like peaks T and B and PARAFAC component C2 (with excitation/emission peak at 281/335 nm) decreased from influent to effluent due to preferential degradation of labile organic compounds, and the C2 decrease was significantly correlated (p < 0.01) with COD removal. The humification index (HIX) increased by ∼190% on average from influent to effluent during normal operation of all of the anaerobic and aerobic DEWATS evaluated in this study, further supporting the preferential removal of labile constituents during treatment. Meanwhile, a newly identified component, C3, with excitation between 410 and 420 nm and emission at 470 nm, increased under normal operation and may represent the formation of coenzyme 420 during biodegradation. Disturbance during scum removal disrupted preferential removal of peak T and resulted in a much lower change in HIX (only 24% increase) from influent to effluent. Recirculation of effluent into the influent stream was found to greatly reduce scum formation in lab-based ABRs while still maintaining a high removal of COD and peak T and producing substantial increase in HIX. The fluorescence-based indices were found to be robust indicators for tracking performance issues in DEWATS.