What distinguishes aerobic treatment systems from anaerobic systems?

The distinguishing feature of aerobic treatment systems lies in their metabolic processes, specifically their use of oxygen for treating waste. Aerobic systems introduce air or oxygen into the treatment process, which allows aerobic microorganisms to thrive. These microorganisms metabolize organic matter more efficiently and effectively, leading to the breakdown of waste and reducing its environmental impact.

In contrast, anaerobic systems operate without oxygen, relying on anaerobic bacteria to decompose organic material. While both processes aim to treat sewage, the mechanisms differ fundamentally. Aerobic treatment typically results in a more complete breakdown of waste products and can reduce pathogen levels more effectively owing to the aerobic bacteria's faster activity in the presence of oxygen.

This clear distinction in oxygen usage between aerobic and anaerobic systems makes option B the correct choice.