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. The standard 5‐day biochemical oxygen demand (BOD5) measurement usually includes a component of nitrogenous oxygen demand (NOD) that can cause over‐sizing of biological processes and under‐evaluation of WRRF process capacity. Carbonaceous BOD (CBOD5) more closely represents oxygen demand associated with biodegradation of organic constituents of wastewater than does BOD5, and therefore should be used as a basis for sizing aerobic treatment processes.