Tennessee Wastewater Operator Practice Exam

Primary clarifiers can affect denitrification by altering which of the following ratios?

1. COD to BOD ratio

2. BOD to nitrate-nitrogen ratio

3. Nitrite to ammonia ratio

4. Organic to inorganic ratio

The correct answer is: BOD to nitrate-nitrogen ratio

Primary clarifiers play a crucial role in the wastewater treatment process by removing suspended solids and some organic matter before the effluent moves to the biological treatment stage, which can include denitrification. During this process, certain ratios become significant in understanding how effectively nitrogen compounds can be transformed into nitrogen gas, thus reducing nitrates in the water. The BOD to nitrate-nitrogen ratio is particularly important for denitrification since this process relies heavily on the presence of suitable carbon sources (measured as BOD) to facilitate the reduction of nitrates. An adequate level of biodegradable organic matter is necessary for denitrifying bacteria to thrive and effectively convert nitrate-nitrogen into nitrogen gas. If this ratio is low, it indicates that there may not be enough organic matter available to support the denitrification process, which can lead to inefficient nitrogen removal. Conversely, a higher BOD to nitrate-nitrogen ratio suggests that there is sufficient carbon present to support denitrification. The focus on this specific ratio emphasizes the interconnectedness of different components of wastewater treatment and highlights how effective primary clarification can set the stage for successful denitrification later in the treatment process.