Setting Realistic Performance Expectations for BNR

Data from 38 full-scale facilities were evaluated to assess general performance capabilities for removal of nitrogen and phosphorus by a wide cross-section of biological nutrient removal processes. Nitrogen removal systems exhibit similar variability in effluent quality as measured by the ratio of maximum month to average effluent total nitrogen and this variability is independent of effluent concentration. Effluent quality variability for phosphorus removal systems based on the relationship between maximum month and average concentrations is similar, but greater than observed with effluent nitrogen. Variability of influent nitrogen and phosphorus concentrations might have little impact on the effluent quality variability. Operational conditions might have the most influence on effluent nitrogen and phosphorus variability.