How to improve the self-purification process of river Ganga?

We all know that self-purification of running water is a set of natural processes that are present in rivers and streams, enhanced by water turbulence that helps increase the amount of oxygen to dissolve in the water.

Most of the time the impurities in waste materials, that are disposed or discharged into the water bodies, get treated automatically by the self-purification process but it needs time, duration and less amount of pollutants.

I would like to know how we can best improve SPP for river Ganga?