Comparison of NMR Analysis and Traditional Wastewater Analysis to Evaluate an Anaerobic Bioreactor Upset

This study investigated the process upset of a benchtop low rate anaerobic reactor by quaternary ammonium compounds (QAC) using typical wastewater quality analysis used by AD process operators and nuclear magnetic resonance (NMR) spectroscopy. NMR is a fully quantifying and non-targeting method to detect changes in wastewater quality. The anaerobic reactor was seeded using anaerobic sludge from a potato processer and operated with a blanched potato wastewater mixture to provide nutrients and substrate. The system was operated for eight weeks to achieve steady state. During steady state, NMR was used to analyze the reactor effluent to generate steady state spectra of effluent quality for comparison during upset conditions. Once steady state was achieved, one dose of Benzolakonium chloride (BAC, a common QAC used in industrial sanitary processes) was added at 15 milligrams per liter (mg/L) in the reactor and the impact of the single dose on reactor performance was assessed. The study found that the reactor performance measured using COD removal efficiency, effluent volatile acid to partial alkalinity (VA/PA) ratio, effluent oxidation-reduction potential (ORP), and methane gas yield indicated a process upset. NMR spectra identified an increase in volatile fatty acids (VFAs) in the effluent as a result of BAC addition. The results indicate that process upset conditions were caused by the single dose of QAC to the reactor at 15 mg/L and the upset conditions persisted for seven hydraulic retention times (HRTs) after the QAC was added.