Treating the sewage is much cheaper option for the
society than to leave it untreated because the un-treated
sewage lead to water pollution and other related diseases and
problems.
The non-treated sewage pollutes rivers, lakes and the sea,
being a cause of diseases transmitted through water.
For the society, the costs of these diseases are much higher
than the cost of the sewage treatment.
One of the most economical systems to treat sewage is the
aerobic treatment system, reservatories kept much oxygenated for
aerobic bacteria to decompose organic material.