Regardless of diel irradiance patterns, influent orthophosphate was relatively stable across the day with hourly mean concentrations that ranged from 0.157 to 0.161 mg-P•L -1 (Figure ), and effluent orthophosphate was consistent with average values of 0.038 to 0.039 mg-P•L -1 (Figure ). Thus, phosphorus removal was stable across 24-hour cycles, including across daily periods (15+ hours) of low irradiance.