At what ammonia concentration does toxicity occur in anaerobic digestion?

In anaerobic digestion, ammonia can become toxic to the microorganisms involved in the process at certain concentrations. The correct threshold for ammonia toxicity typically occurs around 3000 mg/L. This concentration can inhibit the activity of methanogenic Archaea, which are crucial for the conversion of organic materials into methane and carbon dioxide, the primary products of anaerobic digestion.

When ammonia levels rise above this threshold, it can lead to an inhibition of these microorganisms, severely disrupting the digestion process and potentially leading to a failure in the system. Factors such as pH, temperature, and the specific microbial community in the digestor can also influence toxicity levels, but generally, concentrations around 3000 mg/L are recognized as critical.

The other concentration options are either below or above this threshold, where lower levels may not have significant toxicity effects and higher levels could lead to complete inhibition of the digestion process. Therefore, understanding this critical concentration is essential for operators to maintain effective anaerobic digestion processes and ensure optimal performance.