What is the benefit of the production of methane gas in anaerobic digestion?

The production of methane gas in anaerobic digestion offers significant advantages, primarily because methane can be harnessed as a renewable fuel source. Its combustion can generate energy to power other processes within a wastewater treatment plant, such as heating or electricity generation, which can reduce operational costs and reliance on external energy sources. This aspect of methane utilization not only contributes to energy efficiency but also supports sustainability efforts by providing a means to convert waste into valuable energy.

While the other options may highlight important aspects of anaerobic digestion, they do not directly address the primary benefit of methane production. For example, improving water quality is typically more related to the breakdown of organic materials and removal of pathogens than to methane production itself. Similarly, the reduction in solid waste volume is a byproduct of the digestion process but does not focus on methane's utility. Moreover, while the nutrient content of the remaining sludge can be increased through anaerobic digestion, it is not the main advantage of methane production. Thus, the correct answer emphasizes the valuable role of methane as an energy source.