Floating ‘island’ to clean up Neknampur Lake

The floating treatment wetland absorbs nutrients dissolved in the water, such as excess nitrates and oxygen.

From a distance, it appears as if hyacinth has consumed the Neknampur Lake. But a closer look reveals that there is more to the water body than meets the eye. Gently floating on the surface is an artificial ‘island’ with a meticulous selection of plant species.

“The island is in fact a floating treatment wetland (FTW). Several plants on this FTW play the part of cleaning the lake by absorbing nutrients dissolved in the water, such as excess nitrates and oxygen, thereby reducing the content of these chemicals,” says Madhulika Choudhary who heads the non-governmental organisation Dhruvansh.

And with February 2 being observed as World Wetlands Day, the FTW, a joint effort of Dhruvansh, the Hyderabad Metropolitan Development Authority and the Ranga Reddy district administration, supported by other organisations, was inaugurated. The India Book of Records recognised it as the largest FTW in the country.

The FTW, based on the soil-less hydroponics technique, comprises four layers. Floatable bamboo forms its base over which styrofoam cubicles are placed. The third layer is composed of gunnybags. Gravel forms the final layer.

“Hydroponics permits plants to grow only on sunlight and water. There is no need of soil. There are small holes at the bottom to facilitate the flow of nutrients from the water to the plants [the biological uptake process], which are held upright by the gravel layer,” Ms. Choudhary said.

Cleaning agents planted on the FTW are vetivers, canna, cattalis, bulrush, citronella, hibiscus, fountain grass, flowering herbs, tulsi and ashvagandha.

Micro-organisms growing on the 3,000-square foot FTW and the plantroot systems break down and consume organic matter in the water through microbial decomposition. These root systems filter out sediments and pollutants.

The NGO says the FTW is strong and can hold the weight of as many as four people. Compared to sewage treatment plants, this method is much cheaper.

Periodic biochemical oxygen demand (BOD) readings are taken from the Pollution Control Board. When the project began, the BOD was 27 mg/l. “When the first small island was floated here eight months ago, we knew it was too little to clean up the entire lake. We are hoping that in four-six months, there will be a basic change because of the FTW,” Ms. Chaudhary said.