Did you know that at least a hundred litres of water are used up in construction of one square foot of built-up area? In a growing city like Chennai, where you find some construction or the other going on whichever way you look, think of what that means for groundwater resources, which currently constitute the primary source of water supply for the requirements of this water-intensive industry. In a city that is constantly under the shadow of a looming water scarcity, finding alternative, eco-friendly ways to reduce the burden on groundwater tables has never been more important. And that is what Metro Water’s latest proposal for utilisation of treated water from its two Tertiary Treatment Reverse Osmosis (TTRO) plants in Kodungaiyur and Koyambedu could potentially achieve.
Chennai Metro Water Supply and Sewerage Board (CMWSSB) has come up with a novel initiative under which it plans to sell the treated water to the construction industry at a minimal cost. Water from the TTRO plants is known to be safe and reliable. “It is as good as drinking water. While drinking water has Total Dissolved Salts (TDS) of up to 500 units, treated water at the TTRO plants has TDS of only 70 units,” says V G Ramaswami**, Superintendent Engineer, CMWSSB.
The significance of water treatment
Thanks to a good monsoon last year and due to various efforts such as a push for Rain Water Harvesting from the Greater Chennai Corporation and CMWSSB, groundwater tables in the city have seen considerable improvement. “But we should remember that it rains during less than three months a year in Chennai and there is no perennial water body in the city, which makes citizens fall back on groundwater resources whenever there is a drought. The city is prone to drought and we may find ourselves yet again in a situation like the one in 2019. Considering that, groundwater extraction should be limited,” says V G Ramaswami. Treated water can be the alternative here — reusing treated water will reduce the burden on groundwater resources.
Not just construction, TTRO water can, in fact, be used for all non-domestic purposes. “As Chennai is expanding exponentially, relying on the depleting and rain-dependent fresh water and groundwater resources is unadvisable and not sustainable. Borewells as deep as 700 feet have been dug across Chennai for drawing water for various needs, both domestic and otherwise. Rather than going for treated water after exhausting all our resources, why not go for it now?” questions J Saravanan, a hydrogeologist. “Treating waste water is way cheaper than relying on desalination plants,” he adds.
Globally, 80% of used water flows back into the ecosystem without being treated or reused, contributing to a situation where around 1.8 billion people use a source of drinking water contaminated with faeces, according to a report by the United Nations.
Reusing treated water
Water bodies in Chennai have been grappling with sewage water pollution for decades. Across the city, sewage treatment plants treat the raw sewage from households. In many cases, however, the properties are not connected to the sewerage network and rely on private tankers to dispose of sewage. In more cases than not, these end up being dumped in the lakes and waterbodies, leading to water pollution. However even the secondary treated water from the STP have, in certain cases, been found to pollute the water bodies (or groundwater) where it is discharged.
The water from the TTRO, however, is of high quality. The two plants in the city, with 45 MLD capacity each, have been supplying treated water to industries in Poonamallee, which otherwise depend on groundwater and piped water supply from CMWSSB. The secondary treated water from the STPs reaches TTRO plants through large pipelines. At these plants, it is treated through multi-stage treatment schemes, ultrafiltration, Reverse Osmosis and Ozonation, as mentioned on the Metro Water department’s website. The treated water is then supplied via huge underground pipelines that connect the plants to the SIPCOT, Poonamallee.
This initiative, once scaled up, could provide a solution to two critical problems faced by the city: one, of wastage of sewage water and second, indiscriminate groundwater extraction. “The energy-intensive TTRO plants ensure that the wastewater is treated to produce water of high quality that can cater to industrial needs,” says Indumathi M Nambi, Professor, Environmental and Water Resources Division, Civil Engineering department, IIT-Madras.
The demand for treated water in industries is, however, still low. “Currently, we are treating less than 20 MLD water at Koyambedu and 23 MLD water at Kodungaiyur to meet the requirement of the industries. These plants could function at full capacity if there is greater demand,” says Ramaswami.
While the continuing stigma of sewage makes the prospect of using treated water for drinking purposes unlikely, there could be many alternative uses for it at present. Chennai can not only ensure full capacity utilisation of its treatment infrastructure, but also set an example for other metropolitan cities by using treated water in the construction sector, leading to considerably less pressure on its fresh water resources.
“The quality of water used in construction has an impact on the strength of the building. Water with high TDS count cannot be used in construction, as the salts could erode steel and result in cracking of walls,” says Chitty Babu Thangappan, CEO of Akshaya Pvt Ltd. In areas such as OMR where the TDS in piped water exceeds 2000 units, builders ferry water from private water tankers and the Metro Water department. “We pay Rs 1000-Rs 1200 for a kilolitre of water. During periods of water scarcity, the price goes up to even Rs 3000,” says Krishna Kumar T, who works as a civil engineer at a construction company. However, given the quality of treated water yield from the TTRO plants, there should be no issue in utilising that in construction work.
Transportation, however, remains a major challenge if water from the TTRO plants are to be supplied for construction work. “Instead of transporting water to far-off construction sites, that may not be cost-effective, the Metro Water department can focus on builders and precast concrete manufacturers in and around the TTRO plants and sell the treated water to them,” says Suresh Krishn, President, The Confederation of Real Estate Developers Associations of India (CREDAI), Tamil Nadu.
Decentralising water treatment
Countries with no freshwater resources such as Singapore and drought-prone countries such as Israel depend on treated water. Recycled used water meets 40% of the water demand in Singapore; it is utilised for industrial purposes and drinking. In Israel, recycled water is used for agriculture. Half of Israel’s irrigation water, about 500 million cubic meters or 405,000 acre-ft per year, is treated wastewater.
While TTRO technology is a new experiment in India, cities are taking baby steps in reusing used water that goes through secondary treatment. Closer home, Chinnamanur Municipality is using its secondary treated water to irrigate banana plantations. “We irrigate over 20 acres of banana plantations through the treated sewage water. The treatment plant has a capacity of 3.99 MLD and we have been reusing treated water for irrigation since 2013,” said Anbu Karthik P, Site Engineer, Sewage Treatment Plant in Chinnamanur.
To bridge the gap between demand and supply of water, many commercial buildings and large housing complexes in metropolitan cities have started decentralized waste water treatment — treating used water within the premises and reusing this for non-potable uses, as recommended by the Government of India. Central water conservation schemes on mission mode, such as Jal Shakti Abhiyan and Swachh Bharat Mission, emphasize reuse of treated water for non-potable purposes.
“There is still large scope for improvement in apartment complexes in Indian cities, in terms of re-utilisation of treated water. Implementing decentralized facilities for on-site wastewater treatment will facilitate achievement of a circular economy of water in India,” says Lekshmi B, PhD scholar researching wastewater treatment at IIT Bombay.
“As of now, only 30% of India’s urban wastewater is recycled,” says a report from Down To Earth. “Decentralised wastewater management approach can be considered as a sustainable and cost-effective alternative as it treats, discharges or reuses the effluent in the relative vicinity of its source of generation,” the report adds.
The TTRO plants in Kodungaiyur and Koyambedu are centralised. However, as water resource experts do not foresee any significant impact in the space unless operations are scaled up and decentralised, they can only be a part of the solution, albeit an important one. “Every industrial belt should have a wastewater treatment facility,” says J Saravanan. In the meantime, the immediate solution would be to put the two TTRO plants in Chennai to complete use by catering to water-intensive sectors such as construction.
** V G Ramaswami was wrongly referred to as V S Ramaswami in the first published version. We apologise for the unintentional error.