Wastewater aeration is the process of adding air into wastewater to allow aerobic bio-degradation of the pollutant components. Aeration in an activated sludge process is based on pumping air into a tank, which promotes the microbial growth in the wastewater. Aeration provides oxygen to bacteria for treating and stabilizing the wastewater. Oxygen is needed by the bacteria to reproduce quickly and allow biodegradation to occur. The supplied oxygen is utilised by bacteria in the wastewater to break down the organic matter containing carbon to form carbon dioxide and water. The microbes feed on the organic material, forming flocks which can easily settle out. After settling in a separate settling tank, bacteria forming the "activated sludge" flocks are continually recirculated back to the aeration basin to increase the rate of decomposition.Hence, option A is correct.