CWEA Advanced Water Treatment Practice Test 2025 – Complete Exam Prep Resource

The Biochemical Oxygen Demand (BOD) test is a widely recognized method for assessing biological activity in water treatment processes. This test measures the amount of oxygen that microorganisms will consume while decomposing organic matter present in a water sample over a specified period, usually five days at a controlled temperature.

BOD is a critical parameter because it directly indicates the biological activity and the amount of biodegradable organic material in water. A higher BOD value suggests a greater amount of organic material that is available for microbial consumption, which reflects higher biological activity. By examining changes in BOD over time, water treatment operators can evaluate the effectiveness of treatment processes and the health of the microbial community.

Other methods, such as Solids Retention Time, Chemical Oxygen Demand (COD), and Nutrient Ratio Analysis, serve different purposes in water quality assessments but do not specifically measure biological activity. For instance, COD evaluates the total amount of oxygen required to chemically oxidize all organic materials in a water sample, which includes both biodegradable and non-biodegradable substances. Solids Retention Time focuses on the time solids remain in a biological treatment process, and Nutrient Ratio Analysis measures the balance of nutrients required for microbial growth but does not directly assess biological activity like BOD does.