Chennai: Vertical gardens under bridges to use treated sewage

CHENNAI: The city's civic body has rolled out a plan to eliminate defacing of walls and solve at least a small percentage of the sewage problem in the city.
Around 108 piers underneath 14 bridges in the city will have vertical gardens. The catch is that these will be watered with sewage, that will be drawn from, where else, a nearby source on the road.
Senior Greater Chennai Corporation officials said this would cover 5,000 square metres of space on the walls.
The sewage treatment plant (STP) would be a small one with a capacity of around five kilolitres a day, an official said.
"Sewage has rich nutrients, especially nitrogen, phosphorus and potassium, which are necessary for plants. The STP will just decrease the biological oxygen demand (BOD) from 400 to 30, but retain the nutrients," the official said. Treated sewage would also be used from STPs in the corporation's parks for the purpose.
The first such vertical garden is being set up under the flyover on GN Chetty road, the official added. The sewage will be taken from a nearby outlet and pumped to the STP. The gardens will be covered with green and red-leafed plants. This is on the lines of projects in Bengaluru and Nagpur where vertical gardens have come up on metro rail pillars.
On the GN Chetty road flyover's pillars, a metal frame has been installed, which will ensure that the main structure of the flyover is not damaged due to the plants. In future, if need be, the frame and gardens can be removed.
After such vertical gardens are commissioned, the coporation plans to hand over maintenance to any private or public companies for a period of five to ten years, the official added. "The brands can put up small advertisement boards on the piers of the bridges," the official said.
The GN Chetty Road flyover vertical garden has already been given to a private clothing showroom in the vicinity, the official said.