In what scenario is the use of an anaerobic digester most appropriate?

The use of an anaerobic digester is most appropriate in scenarios involving organic solid waste. Anaerobic digesters create an environment devoid of oxygen that allows microorganisms to break down organic materials, producing biogas—primarily methane—and a digestate, which can be used as fertilizer. This process is particularly effective for handling various types of organic waste, such as food scraps, agricultural residues, and wastewater sludge.

In contrast, anaerobic digestion is not ideal for scenarios requiring high temperatures, which are more characteristic of thermophilic aerobic processes. When high levels of nitrates are present in wastewater, other treatment methods, such as biological nutrient removal, are generally employed rather than anaerobic digestion, which is not specifically designed for nitrate removal. Additionally, anaerobic digesters are not utilized for heavy metal decomposition; other specialized processes are needed for those contaminants, as heavy metals do not breakdown in the same way organic materials do and can actually inhibit the functioning of anaerobic digesters.

Therefore, the effectiveness of anaerobic digestion in processing organic solid waste underlines its appropriateness for this type of material, making it the correct answer.