In what scenario would you use an anaerobic digester?

Using an anaerobic digester is most appropriate in the scenario of stabilizing and reducing biosolids. Anaerobic digestion is a biological process where microorganisms break down organic matter in the absence of oxygen. This process is particularly effective for treating solid waste, such as biosolids generated from wastewater treatment, as it not only reduces the volume of these solids but also converts them into biogas, which can be captured and used as a renewable energy source.

Additionally, anaerobic digestion results in the stabilization of biosolids, making them safer and more manageable for disposal or application to land. The output of this process, the digestate, can also be further treated and used as a soil amendment, providing an environmentally friendly disposal method.

The other scenarios do not align with the primary function of anaerobic digesters. For instance, treating high levels of oxygen demand typically requires aerobic processes, while polishing treated effluent is achieved through methods designed to remove remaining impurities in the presence of oxygen. Nitrogen removal, on the other hand, often involves specific biological processes known as nitrification and denitrification, which also rely on aerobic and anaerobic conditions but are not the primary purpose of an anaerobic digester.