Tennessee Wastewater Operator Practice Exam

If the organic loading rate to a trickling filter is reduced from 1.5 kg/m³/d to 0.7 kg/m³/d, what is the likely effect on effluent ammonia levels?

1. Effluent ammonia will increase

2. Effluent ammonia will remain the same

3. Effluent ammonia will decrease

4. Effluent ammonia will fluctuate

The correct answer is: Effluent ammonia will decrease

Reducing the organic loading rate to a trickling filter from 1.5 kg/m³/d to 0.7 kg/m³/d is likely to lead to a decrease in effluent ammonia levels. This is primarily due to the relationship between organic loading and the activity levels of microorganisms within the system. When organic loading is high, there is an abundance of substrates available for microbial consumption. These microorganisms, particularly nitrifying bacteria, convert ammonia into nitrite and then into nitrate through the process of nitrification. A high organic loading rate can sometimes lead to conditions that are less optimal for these bacteria, which can result in incomplete nitrification and thus higher levels of ammonia in the effluent. As the organic loading rate is decreased, it provides a more favorable environment for the growth of nitrifying bacteria. With less organic material to compete with, these beneficial bacteria can thrive and effectively oxidize ammonia at lower loads. Consequently, the reduction in ammonia levels in the effluent reflects improved treatment efficiency. This decrease in organic loading can also lead to more steady-state conditions within the trickling filter, which can reduce fluctuations in effluent quality, particularly ammonia concentrations. Thus, the overall effect of lowering the organic loading rate is a decrease in the effluent