What is the function of activated sludge formation in treating...

For more than a hundred years, microbes have been used to treat sewage (waste water) by the process of activated sludge formation and this helps in recycling of water in nature.You are aware that due to increasing urbanisation, sewage is being produced in much larger quantities than ever before. However the number of sewage treatment plants has not increased enough to treat such large quantities. So the untreated sewage is often discharged directly into rivers leading to their pollution and increase in water-borne diseases