The natural drains in the cities are polluted due to inappropriate disposal of liquid and solid wastes. Three polluted drains carrying wastewater from the surrounding communitites and industries in Pune city were selected to treat using ecological principles - symbiotic relationships of plants and microbes. The innovative technique - horizontal filtration - Green Bridge - was employed to control the pollution in drains. Its uses the locally available materials like stones, sand, soil, plant fibres and plants with microbes. A number of green bridges are installed to trap the pollutants by three filters - stone and sand, plant fibres and roots of live floating plants. The microbial films formed on the roots of plants, fibres and stones are found to be actively participating in biodegradation and bioconversion of pollutants. It is noted that the reduction COD is possible upto 90%. This technique is useful to control the pollution where modern, conventional aerobic or anaerobic systems are not economically feasible.