Wetlands are essential for groundwater recharge, collection of essential nutrients from water runoffs, and prevention of soil erosion. Despite such importance, wetlands in India are depleting. The depletion of wetlands poses a threat of water scarcity across the nation. However, some cities are taking this issue seriously. Delhi Jal Board, Irrigation and Flood Control Department and other authorities in the national capital came up with a feasible solution to recharge groundwater by reviving wetlands and transforming them into natural STPs
Delhi has seen unprecedented expansion and this gradual rise in population has led to an even greater burden on the natural resources of the city. The gap in the city’s water demand and supply resulted in people resorting to groundwater extraction using borewells. A Central Groundwater Board (CGWB) report stated that the groundwater levels in more than 15 per cent of Delhi’s areas are now alarming, below 40 meters. With minimal focus on replenishing groundwater levels, Delhi is on the verge of a severe water crisis..
In order to avoid this, Delhi Jal Board (DJB), on December 24, 2018, announced that the water authority would be rejuvenating 159 natural wetlands across the city.
Why are wetlands the way forward
Wetlands worldwide have a reputation of being “Nature’s Kidneys” as they essentially remove polluting nutrients and sediments from surface and groundwater. These natural structures, when spread out, reduce soil erosion. Another interesting observation one can make is how wetlands are essentially mini-ecosystems on their own. Plants and aquatic life thrives in abundance in these settings and these species are instrumental in purifying the water which then recharges the groundwater reserves. As sediment, excess nutrients and chemicals flow off of the land and wetlands filter the runoff before it reaches open water. Nutrients are stored and absorbed by plants or microorganisms. Groundwater recharge occurs through mineral soils found primarily around the edges of wetlands. Wetlands demonstrate high water volume restoration rate, which means that a smaller wetland can affect a greater area. Researchers have discovered groundwater recharge of up to 20 per cent of wetland volume per season.
Current state of Wetlands
Wetlands are threatened to a great extent, according to World Wildlife FundIndia (WWF-I), who report that loss of vegetation, salinization, excessive inundation, water pollution, invasive species, excessive development and road building, have all damaged the country’s wetlands. For the national capital, the Delhi Climate Action Plan, published in 2009, identified 621 wetlands and most of them have dried up by 2009 and are now beyond revival. 159 of these pre-existing wetlands were identified by Delhi Jal Board (DJB) and, in December 2018, the board rolled out a `376 crore plan to rejuvenate these in a bid to “aid groundwater recharge and boost water reserves of the city”, according to Arvind Kejriwal, Chief Minister and DJB chairperson.
Another measure that the government is planning to take is to convert the area around the lakes to public spaces. The total area of water bodies will be 350 acres, holding 1,581 million liters. “Apart from rainwater, treated water from STPs will be polished using natural wetlands and other methods to maintain the water levels in the water bodies throughout the year. The step will improve depleting groundwater levels of Delhi apart from making Delhi sustainable for water supply. Excess water from the ground will be taken out to augment Delhi water supply wherever required,” read a statement released by the Chief Minister.
The first of such natural sewage treatment plants (STPs), which would treat sewage water chemical-free and then supply the treated water to the wetland was set up in Bawana district near the Ghoga wetland in June, 2019.The natural STPs will be maintained by the Irrigation and Flood Control
(I & FC) Department. A similar establishment had been made in Rajokri in late 2018, but it was at a smaller level.
The Delhi Climate Action Plan, published in 2009, identified 621 wetlands and most of them have dried up by 2009 and are now beyond revival. 159 of these pre-existing wetlands were identified by Delhi Jal Board and, in December 2018, DJB rolled out a `376 crore plan to rejuvenate these in a bid to aid groundwater recharge and boost water reserves
Bawana’s natural STP
The plant derives sewage from the Ghoga drains, treats it and then uses the treated water to rejuvenate the Ghoga wetland. Authorities are reckoning that the pilot project has turned out to be a success and the state government is planning to add at least 16 more STPs in the city to treat the unchecked waste water of the city.
The STP is 300 meters long and 5 meters wide. Sewage is routed from Ghoga drain and is led into a sedimentation tank where it is stagnated for some time for effective sedimentation of larger solid particles. As the sewage flows through it slowly, the heavy solid waste particles gradually sink to the bottom. This phase of the treatment is called the Primary Phase.
For the Secondary treatment, the waste water is further directed to multiple chambers where water flows through beds of pebbles of various sizes. Four chambers, separated by screens, house various types of flowers and small microbes which utilize minute organic impurities that cannot be separated from the sludge by movement on the pebbles as food, converting them into carbon dioxide, water, and energy for their own growth and reproduction. The treated water is then redirected to the Ghoga wetland, which is adjacent to the STP.
Usability of the Natural STP
Setting up and maintenance cost of such plants is comparatively lower than the traditional STPs. Mechanical devices are not used in these treatments, thus reducing the maintenance cost. The only limiting factor is the availability and the cost of land to place the treatment plants. Another aspect that requires improvement is the operational capability of the plant. The plant in Bawana can only treat 10 lakh liters of waste water, which is approximately the waste generated by 50 households in a single day. But, the STP has been successful in cleaning out the sewage of Bawana, which has been highly polluted due to industrial waste, to a sufficient degree. “While the biochemical oxygen demand (BOD) levels in a normal drain are around 220 mg/l, here it is 332 mg/l, indicating industrial waste. After the treatment, the BOD levels in the outlet water is 31 mg/l,” said a
Depleting of wetlands by encroachment or ignorance is evident all over India. Delhi gives a sliver of hope in the present scheme of things. The project may not be on a large scale but small cities and towns can surely take advantage of such a system because of low expenditure involved in setting up and in maintenance. Jairam Ramesh, former environment minister, stressed on its significance this year in the Rajya Sabha and said, “There is loss of wetland across the country due to various man made factors like excessive hydrological alterations, unregulated construction and haphazard urbanisation which further cause underground water depletion”. He added “despite judicial intervention, wetlands have received no due protection.”