Making every drop count

Bengaluru: Every apartment generates almost as much sewage as it consumes. In smaller apartment communities, there is not enough space for bigger gardens and recharge wells, making it difficult to use the treated water for gardening or recharging. Similarly, most apartments do not have enough dual plumbing to make flushing water difficult.

Srinivasan Sekar, a water consultant based in Bengaluru, recalls the wastewater reuse system in T-ZED Homes in Whitefield, which is an ideal solution to this that all communities can emulate.

The project at T-ZED, which began in 2012, aims to eliminate the cycle of water going through drainage to lakes, then to borewells and back to the community through tankers. Apart from mopping, car washing, gardening and other direct uses, the remaining treated water is sent to a closed-loop recycling system.

Chlorination in the sewage treatment plant (STP) helps kill biological impurities. The treated water later runs through a series of filters: sand, charcoal and ozonisation. It then goes to an industrial reverse osmosis plant with more filters and membranes. After mixing with borewell water, the water goes through RO before use and becomes available for everything, including cooking, drinking, bathing, etc.

“The elimination of dissolved solvents and bacteria in the pre-RO filtration process makes it easy for the RO system to clean the water better, and the RO membrane lasts longer,” he says. 

Clay pots on sale amid rising temperature and water crisis in Malleshwara in Bengaluru.

The RO reject water, about 40-50 per cent of the treated water, is used as primary water for the garden and groundwater recharge, so no water is wasted. The community has rainwater recharging systems. Although the water wasted in gardening has to be replenished, the requirement becomes lower due to this system.

With quality controls in place, communities can ensure that water from this system is of better quality than borewell water, which takes months to percolate and recharge and yet has a higher level of dissolved solvents.

“After we came out with this system in November 2012, we discovered that Singapore started doing it on a city scale in December 2012. So this is a scaleable solution for any city,” says Sekar.

The campus uses 45,000-60,000 litres per day and would require 10-12 tankers a day. However, even with the borewells in the community gone dry during summer, the community just needs 3-4 tankers, amounting to a maximum of 30,000 litres of fresh water per day, with almost half the need fulfilled by the treated water.

Little drops of water

Every home uses water filters which emit reject water in 1:3 ratio. Bali Raghotham, a lake activist from East Bengaluru, collects the reject water from the reverse osmosis (RO) plant at his home. “We are a big family and get an RO reject of 30 litres daily. I collect this and other mildly used water and carry it to the lakeside every two days to water the plant,” he says.

Cauvery drinking water supplying in mini trucks by BWSSB in Bengaluru.

This amounts to 60 litres of water per two days. He says he initially thought this was a very small amount and may not matter much, but now he realises that it is helping in the current situation.

He says many other inspired citizens in the vicinity try to save every drop, such as RO reject water and water used for washing rice. They use it to water saplings on the beds of lakes such as Varanasi and Seegehalli. During a cruel summer like the current one, every little drop helps, he says.

What blocks the sale of treated water?

Meanwhile, the government has permitted the sale of treated water by private apartments. Rajagopalan, president of J P Nagar Residents Welfare Association, lists the wastewater reuse plan's drawbacks. Many communities in Bengaluru do not manage STPs properly and maintain water quality. “It is a challenge to ensure the quality of output from over 2000 private STPs, which are rarely monitored,” he says.

The cost of recycling water is another issue. “The required delivery infrastructure, including piping, transport, and other overheads, needs to be assessed and compared before its use for a specific purpose,” he says. He adds that the entire construction industry should be mandated to use treated water, not just large ones.

Another problem is the enforcement. The BWSSB’s notification mandating modular Sewage Treatment Plants and dual piping in residential buildings with 20 or more houses/apartment units with retrospective effect was met with resistance and never fully implemented. Now it is 120 units.

“This makes sense because of the issues in operating smaller STPs and quality problems,” says Shubha Ramachandran, a water consultant and a member of Biome Trust.

“We have all the mandates, acts, and rules, but enforcement is severely lacking. KSPCB claims to be at least 50% short-staffed to monitor the STPs' functioning. They might need to mandate emerging technology for remote monitoring,” says Rajagopalan.

“As BWSSB now allows 50 per cent sale of STP-treated water from apartment complexes, one innovative solution is for apartments to use a closed-loop system to use the excess treated water from nearby apartments for shortage instead of tankers,” says Srinivasan Sekar, a water consultant.

Shubha Ramachandran, a water consultant and a member of Biome Trust, says the mandate for selling treated water is good. She lists many other solutions for treated water, such as mixing it with fresh water for laundries and using it in cooling towers.

“The adoption of several past research studies, some currently underway, is looking into the change in consumer mindset and aversion to wastewater reuse. There should be a higher degree of awareness and consumer education on treated water in our society,” adds Rajagopalan. He hopes the conversation on wastewater reuse does not die when it rains.

‘Quality norms are critical’

WELL Labs and the Swiss Federal Institute of Aquatic Science and Technology, in partnership with Bangalore Apartment Federation (BAF), surveyed sewage treatment plants (STP) in the Yelahanka zone.

A woman tries to catch a stream of water falling from overhead tank at Sampagi Rama Nagar in Bengaluru.

The study used the Karnataka State Pollution Control Board’s data from 2021 as a reference to get an overview of the decentralised STPs in the area. The KSPCB list showed that 506 apartments had applied for consent for the operation. Out of them, 182 were being constructed with an STP.

“The WELL Lab’s ground survey revealed that the constructed number is reasonably accurate, as we could map 175 apartments on the list and survey STPs for 60 of those apartments,” says a note from WELL Lab shared with DH.

The survey showed that the apartments with systems smaller than 250KLD had almost 60 per cent of water left after reusing treated wastewater for landscape irrigation and toilet flushing. This would inevitably end up in drains and lakes.

The new policy for wastewater sale says the quality should be maintained as per the end use but does not list the parameters. There are currently no standard operating procedures for checking the water quality from private STPs.

"The National Framework on the Safe Reuse of Treated Water by the Ministry of Jal Shakti has outlined some of the standards for reuse. For existing industrial reuse, it points to the CPHEEO manual and standards yet to be set to an upcoming guideline on 'Treated Industrial Wastewater Reuse' drafted by the Central Pollution Control Board (CPCB). The framework also advocates for reuse in construction and specifies that the Central Public Works Department (CPWD) will develop guidelines for standardisation and use of treated used water (TUW) in construction industries," says Shreya Nath, managing partner of Urban Water Programme, WELL Labs.