Only a year ago, images of snow-white toxic foam floating over the Yamuna river in Delhi had shocked the world, waking it up to the reality of the water population in the country’s capital. According to the Delhi Jal Board (DJB), one of the main reasons behind this situation was untreated sewage, something that the city’s lakes and rivers have been struggling to tackle for years.
However, in the last few years, The Delhi government has been able to follow a steady path of improvement through various lake rejuvenation efforts spearheaded by the DJB, Irrigation and Flood Control Department (IFCD) and several citizen groups. And one the pioneering projects that set the ball of positive transformation rolling was the Rajokri Lake project.
The Model Project
Around 30 km away from the city, near the Delhi-Gurugram border, Rajokri, till 2017, was home to a dying waterbody that had suffered years of toxic abuse. Clogged drains led up to the turbid pond struggling under a filthy blanket of plastic waste and rotting sewage.
However, under all the filth was a reservoir of potential, something that a team including DJB’s technical advisor Ankit Srivastava and architect Mriganka Saxena envisioned. Under their guidance, the DJB along with IFCD started the transformation of the Rajokri pond into Delhi’s first-ever decentralized sewage system.
“Delhi has approximately 600 water bodies and the eventual goal is to revive all of them. However, there was no model of holistic revival that we could follow. So, instead, we created an in-house team to work on making our own model best suited for the city’s condition, and that’s how the Rajokri project was started as a pilot in 2017,” says Ankit, who is a graduate of IIT Bombay, in environmental science and engineering.
He adds that owing to the limited annual rainfall received by the city, one could not have depended on conventional methods of water-body rejuvenation, which often involves cleaning the affected areas and letting it get recharged with rainwater. The multifold goal was to create a lake that could efficiently treat all the sewage water flowing in, while also containing clean water throughout the year. It was also supposed to serve as an inclusive community centre and a natural ecosystem.
And so the revitalisation project was divided into two major components– the construction of a purification system and landscaping of the surrounding areas to not only enhance aesthetic value but also make long-term management of the lake more sustainable.
Explaining this, Mriganka who was handling the latter segment with a focus on the project’s long-term sustainability says, “This project had to both enhance the landscape of the area but also benefit the people on a long-term basis. Hence the design was strategized in a manner that the structure could easily be maintained by the surrounding communities. Additionally, there were a number of environmentally responsible and sustainable guidelines that we were following under the guidance of National Green Tribunal (NGT). From doing the green landscaping with native plant species to creating percolation pores for groundwater recharge, a number of elements were added to enhance the value of the project.”
Innovation in & Around The Lake
Historically, Rajokri was a mining area surrounded by hills. So during the monsoon season, rainwater would flow through the slopes into this waterbody. Meanwhile, over a period of years as more settlements began to come up around the area, the sewage would also flow into the same water, leaving it dirty and contaminated.
Talking about their design strategy based on this reality, Ankit says, “Delhi receives rainfall for less than a month, so it is important to focus our efforts on treating the wastewater, instead of solely relying on rainwater. So the first part of the plan was to clean the water coming from the sewage at the STP through a unique SWAB (scientific wetland system with active bio-digester) technology. During monsoons, the water recharging the lake is anyway 15-20 times more, and our rainwater harvesting system installed on-site ensures removal of stilt and enhances percolation. Other times of the year, the system of STP allows it to maintain a stagnant level by containing the purified sewage water.”
A scientific wetland system with active bio-digester, this technology is a natural alternative of sewage purification to the conventional chemical treatment previously used by DJB. This involves feeding sewage into an underground sedimentation tank equipped with a bio-digester to break down and decompose solid waste components in the water. This is then complemented with the use of wetlands and mechanised aeration systems to naturally clean the water.
In Rajokri lake’s case, the wetland ecosystem was created with plants like spider lily and typha latifolia, a layer of gravel-lining zigzag to filter the water and a biofilm to process all pollutants. Once the water is pushed from the sedimentation tank into the wetland using solar pumps, the gravel layer works to isolate and immobilize heavy metals and other organic material in the water to an acceptable level.
“The zig-zag design through three terrace garden-like steps ensures that water gets to spend maximum time in the wetland. At its outlet, the water is almost clear with a BOD (biochemical oxygen demand) of 20ppm,” says Ankit in this report.
According to a 1996 book called the Treatment Wetlands by Robert H. Kadlec, Scott Wallace and Robert L. Knight, such wetlands are very effective in removing inorganic nutrients, heavy metals, particulate organic matter, suspended solids, dissolved organic carbon, etc. These wetlands have submerged aquatic macrophytes (aquatic photosynthetic organisms) with tiny cuticles that capture metals from the water surface and are also hardy enough to survive harsh conditions of pollution.
Additionally, in order to contain the algal bloom and remove trace pollutants and phosphates from detergents that go into the raw sewage, the DJB team introduced unique purification islands in the water body. These islands are basically rafts made out of a 2X2-meter PVC pipe framework with geo-netting that supports knots of hormone-treated plants like canna and cyperus. These plants not only increase nutrient uptake and accelerate the growth of other beneficial aquatic plants but also absorb pollutants and create a balance by preventing eutrophication (excessive enrichment of waterbody with minerals and nutrients that allows excessive growth of algae and results in oxygen depletion). According to Ankit, the objective is to make the water clean and suitable enough to introduce fishes into it and enhance its natural ecosystem.
Owing to all these innovative measures, the Rajokri sewage treatment plant now facilitates purification of 600 kilolitres (6 lakh litres) of raw sewage daily feeding the waterbody.
Community Involvement & Impact of the Lake
Spread across 9,446 square meters of redeveloped public space, including 2,000 square meters of the water body, the Rajokri lake is now a stellar example of innovation meeting grassroots level social development.
From an amphitheatre, an open gym, green play area and a bioswale rain garden, to changing rooms and inclusive spaces near the Chhath ghat, the Rajokri lake in its entirety is made keeping in mind the needs of the community living nearby.
For instance, Mriganka adds how based on one of the feedback received from the community, her team worked to separate the treated water body from an embankment assigned for the commonly practised Chhath festival rituals. The sandstone embankment tactfully creates the divide and water from the main lake is then pumped into the embankment situated at the bottom of the amphitheatre-cum-Chhath ghat.
While their efforts have yielded the expected results, Ankit adds that he was pleasantly surprised to see an environmental and sociological impact after the completion of the project in 2018.
“After the waterbody completely transformed, we were surprised to notice that 10 to 15 different species of birds had begun to migrate here. The wetlands were installed to encourage this and attract more species of birds and insects that would enhance the biodiversity of the area,” says Ankit.
He adds that prior to the project the area was primarily a dumping ground and hub for antisocial elements and that its transformation completely put an end to it. “One of the major challenges while working on this project was to tackle heavy encroachment. Plus it had become a hub for drunkards and several anti-social elements making it quite unsafe. Once, all of that was taken care of we began to realize its sociological impact on the community as well. One of the best feedbacks received was how the women in the area began to feel more safe crossing the location after sundown.” he adds.
According to DJB officials, a conventional project of this scale would have cost at least Rs 4 Crore, while the total expenditure of the Rajokri lake stands at Rs 1.6 crore, making it a cost-effective and innovative model for others to replicate. Owing to this, Rajokri lake recently received the excellence award from the Jal Shakti Ministry. With this success in place, Ankit and his team are now planning to complete 50 more water bodies in the next 5 months and also create 6 lakes across the city, by the end of the year.
(Edited by Vinayak Hegde)