Key indicators of stable performance included near-neutral pH throughout the system, sufficient residual alkalinity in the EcoRecover effluent (>100 mg•L -1 as CaCO3), and a steady daily rhythm in the DO concentration in the PBR effluent (Figure ). In particular, the cycling of DO concentration in the PBR effluent was a readily available indicator for operational staff given that the DO concentration followed the same pattern as diel lighting intensity when the microbial community is photosynthetically active (Figure , Figure ), often reaching 10-20 mg•L -1 of DO during peak daylight hours. Although the mix tank was intermittently sparged with air to achieve mixing, the combination of sparging, influent DO (from SBR effluent, internal recycle from the PBR effluent, RAA from the membrane tank, and centrate; Figure ), and oxygen consumption (which accompanies stored carbohydrate consumption) resulted in relatively stable DO in the mix tank across individual day-night cycles (Figure ). Periods of process upset or variable performance were defined as periods of prolonged or intermittent exceedance of the 0.04 mg-P•L -1 effluent target, respectively. Although not the focus of this study, the system was susceptible to process upsets driven by upstream changes to the wastewater treatment process (e.g., reduction in SBR settling time that resulted in TSS concentrations >100 mg-TSS•L -1 entering the EcoRecover process), high influent concentrations of a disinfectant (quaternary ammonium), and biological drivers (including grazers 60 ). Periods of process upset or variable performance were often characterized by variable or basic pH, loss of DO diel rhythm (e.g., as seen in November 2022, Figure ), and at times included insufficient