Carbonaceous vs. total biochemical oxygen demand as a basis for WRRF design and performance monitoring

The standard 5-day biochemical oxygen demand (BOD₅ ) measurement of water quality is used widely as a design parameter for water resource recovery facilities (WRRFs). This measure usually includes a component of nitrogenous oxygen demand (NOD) that can cause oversizing of biological processes and under-evaluation of process capacity. Carbonaceous BOD (CBOD₅ ) more closely represents oxygen demand associated with biodegradation of organic constituents of a wastewater than does BOD₅ and therefore should be used as a basis for sizing aerobic treatment processes. Nitrogenous oxygen demand or reduced nitrogen content should be used as a loading and process performance parameter for nitrogen removal processes. PRACTITIONER POINTS: Oxygen demand for aerobic biodegradation reactions typically is divided into two major categories-carbonaceous biochemical oxygen demand (CBOD) and nitrogenous oxygen demand (NOD). Use of BOD₅ as a design parameter and CBOD₅ as an effluent water quality parameter distorts the true performance and loading rate capacity of a treatment plant. Carbonaceous BOD (CBOD₅ ) more closely represents oxygen demand associated with biodegradation of organic constituents of a wastewater than does BOD₅ and therefore should be used as a basis for sizing and evaluating the performance of aerobic treatment processes. Nitrogenous oxygen demand or reduced nitrogen content should be used as a loading and process performance parameter for nitrogen removal processes.