Natural streams, rivers and lakes have their own in-built purification system which consists of natural slopes, stones for biological growth and complex food web help in the purification process. This food web is nothing but utilization of one's waste by another as its own food. Nature has her own living machinery of detritivorous microbes and other living species to consume wastes. These principles have been harnessed in the treatment of polluted streams.
Green bridges are developed using fibrous material with stones. All the floatable and suspended solids are trapped in this biological bridge and the turbidity of flowing water is reduced. Green plants on the bridges increase the DO level in water, which in turn facilitates the growth of aerobic organisms, which degrade organic pollutants. Sandeep Joshi, director, SERI (Shrishti Eco-Research Institute) has developed this technology and has received a patent for it.