Floating island of plants to clean Mumbai’s river which is 100 times more polluted than safe limit

Mumbai city news: Citizens placed plants, which were going to be uprooted for Metro construction, in 500 bottles to create the cleaning device

A 25-square-foot floating island made of plants, which were going to be uprooted for Metro construction, was placed in Poisar river on Sunday as an experiment to see if it could be used to clean the polluted waterbody. The plants were uprooted from a Metro rail construction site in Andheri and were put in 500 discarded plastic bottles which were tied together to create a makeshift ‘mop’.

The 25-square-foot floating island in Poisar river in Mumbai. (Pratham Gokhale/HT)

The Poisar, which flows through Kandivli and Borivli, is polluted with untreated sewage from residential and industrial areas. HT had reported that a study by Environmental Policy and Research India (EPRI) had showed that pollution in the Poisar river was 100 times the safe limit.

Members of River March, a group which aims to revive Mumbai’s four rivers — Poisar, Oshiwara, Mithi and Dahisar — said that they have used a wetland plant species – canna indica – to create the floating wetland. “The plants in the wetland provide a peculiar habitat for beneficial microorganisms in the root-zone (which also pump oxygen from the atmosphere into the bed) and jointly purify the sewage while the plants are automatically nurtured by the nitrogen and phosphorous in the sewage,” said Shyam Asolekar, professor from the Indian Institute of Technology, Bombay.

Members of River March group used 500 plastic bottles to make the floating treatment wetland on Sunday.

Describing the operation, Sagar Vira, a Kandivli resident, said, “We divided our team in two groups. One group collected and cut the plastic bottles from the base to make conical funnels to hold the plants and the other team went to Andheri to get the plants.”

Borivli resident and another volunteer Chetan Gandhi said they used an excavator machine for the work. Pollultion experts said floating islands of vegetation can be used to clean up water bodies.

What is a floating treatment wetland?

A constructed wetland bed is a natural treatment system that does not need energy or chemicals to clean wastewater

It traps the foul odour below the wetland bed and treats sewage through a continuous biotechnological process once the wastewater is released into the wetland bed.

What does it do?

Making use of waste material helps reduce water pollution in river as these floating treatment wetlands remove nutrients, suspended solids, metals like Zinc and Copper and excess ammonia (NH3)

The process helps increase availability of oxygen to protect aquatic life

Floating wetlands have now been approved as a storm-water best management practice (BMP) both within the country and abroad

Proposal to clean Poisar using artificial wetlands

Last week, the River March group submitted a proposal to the storm-water drain (SWD) department of the civic body suggesting that artificial floating islands be made along the entire 1.5 km stretch of the Poisar river

Officials from Brihanmumbai Municipal Corporation’s SWD department said they were interested in using such a technique. “This is a cost-effective measure to reduce water pollution. We will check the results of the pilot project and if positive, sanction it to contractor for all four rivers in the city,” said a senior civic official from SWD department.