Bacteria, plants to clean up polluted canals around city

‘Effective, But Less Expensive’

Kolkata: With lack of adequate land to set up treatment plants to keep the drianage outfall canals clean as per National Green Tribunal (NGT) guidelines and to prevent river water from getting polluted, the Kolkata Metropolitan Development Authority (KMDA) is introdcing bio- and phyto-remediation process in which micro-organisms and plants are used to clean and purify contaminated and polluted water. The authorities have identified eight such outfall canals in the Kolkata Metropolitan Area (KMA) for this project.

The canals identified are Chorial canal, Najir canal, Moktarpur canal, Bag canal, Bally canal, Khardah canal, Bager canal and Baidyabati canal. Of these, work order has already been issued for six canals and process is on to engage agencies for Bally and Baidyabati canals.

KMDA officials said though there are treatment plants to purify small drainage channels, a huge amount of land is required to set up treatrment plants to purify outfall canals. “There is not enough land to set up sewerage treatment plants (STP). It is time-consuming and expensive, with each STP along with its networks and pumping station costing at least Rs 4 crore,” said an official.

Officials said the excess rainwater during monsoon and waste water in dry season flow into rivers. It is difficult to create new channels to divert the drainage water into the treatment plants. “It is for these reasons that it has been planned to use bio- and phyto-remediation process to purify the canal waters, which is less expensive and less time-consuming,” an official said.

Experts said that these approches are eco-friendly. Bio-remediation involves infusing certain bacteria or micro-organisms in the water. These micro-organisms consume the pollutants and break it down, cleaning up the water. And phyto-remediation uses various plants to oxidise the water and reduce contamination.

Officials said it would cost a maximum of Rs 1 crore to set up bio- and phyto-remediation system for each canal. “A 500m to 1km stretch of each canal will be used to introduce the system. For bio-remediation, a screen will be placed in the canals that would infuse the microorgamisms in the water. For phyto-remediation, a small island with some specific plants and grass will be created in the canal,” an official said. The entire process will take about six months to be executed.