From a distance, it might appear as if hyacinth has consumed the Neknampur Lake in Hyderabad city. But a closer inspection will reveal that there is more to the water body than meets the eye. Gently floating on the surface is an artificial ‘island’ made of meticulously chosen plant species.
“The island is a floating treatment wetland (FTW). Several plants on this FTW help clean the lake by absorbing nutrients such as excess nitrates and oxygen present in the water. They thus reduce the content of these chemicals,” says Madhulika Choudhary, who heads Dhruvansh, an NGO.
The FTW on Neknampur Lake was inaugurated on February 2, World Wetlands Day. Measuring 3,000 sq. ft., the FTW is a joint effort of Dhruvansh, the Hyderabad Metropolitan Development Authority, the Ranga Reddy district administration and other organisations. It has already been recognised by the India Book of Records as the largest FTW in the country.
Based on the soil-less hydroponics technique, the FTW comprises four layers. Floatable bamboo forms its base, over which Styrofoam cubicles are placed. The third layer consists of gunny bags. The final layer is of gravel. “Hydroponics permits plants to grow only on sunlight and water. There is no need of soil. There are small holes at the bottom which facilitate the flow of nutrients from the water to the plants (biological uptake process), which are held upright by the gravel layer,” Ms. Choudhary says.
Cleaning agents planted on the FTW include vetivers, canna, cattalis, bulrush, citronella, hibiscus, fountain grass, flowering herbs, tulsi and ashvagandha.
Micro-organisms growing on the FTW and plant root systems break down and consume the organic matter in the water through microbial decomposition. The root systems filter out sediments and pollutants. The NGO claims that 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 (100 sq ft) was floated here eight months ago, we knew it was too little to clean up the entire lake. We are hoping that in four to six months there will be a fundamental change because of the FTW,” Ms. Chaudhary says.