TOC Talks: Insight and Efficiency at the City of Boulder’s Wastewater Treatment Facility

The city’s 75th Street Wastewater Treatment Facility (WWTF) is among many facilities across the world facing the challenge of carbon management. Enhanced nutrient removal requires the right amount of carbon to be present at the right process area at the right time and in the right form, ideally balanced with supplying carbon to solids stream energy recovery systems. Diurnal patterns of secondary influent nitrogen and carbon can be offset enough to create significant differences in the C:N ratio from one time of day to another, contributing to carbon limitations in nutrient removal processes. Online process monitoring of secondary influent total organic carbon (TOC) and ammonia at the city’s WWTF have unveiled these impactful fluctuations, previously masked by daily composite sampling. Understanding the dynamics of process loading presents opportunities for enhancements in internal carbon management, reductions in external carbon dosing, and improved nutrient removal efficiency.TOC is a faster, easier, and more accurate alternative to biochemical oxygen demand (BOD). The City of Boulder (city) has proposed the inclusion of its long-term site-specific correlations between BOD and TOC and between carbonaceous BOD (cBOD) and TOC in the renewal of its Colorado Discharge Permit System (CDPS) permit with the purpose of allowing the city to use linear regression equations from these correlations to convert TOC data into BOD and cBOD data. TOC testing will provide more timely information to operations staff for process control and process optimization and will provide additional staff time and budget to the city’s wastewater laboratory staff to more easily accommodate the additional analyses that will be required under Colorado Regulation 85 for regulatory compliance and process control and optimization.