Despite the delays and challenges, it is possible to clean the Yamuna in Delhi to bathing standards and achieve water quality to support propagation of aquatic life by 2025, experts have said.
Treating all the domestic wastewater and industrial effluent and further cleaning it using in-situ techniques can help achieve the target, they said. Delhi Chief Minister Arvind Kejriwal and Water Minister Satyendar Jain have on several occasions said the river will be cleaned to bathing standards by 2025.
The Yamuna can be considered fit for bathing if biological oxygen demand (BOD) is less than 3 milligram per litre and dissolved oxygen (DO) is greater than 5 milligram per litre.
Dissolved oxygen (DO) is the amount of oxygen available to living aquatic organisms. Aquatic life is put under stress if DO levels in the water drop below 5 milligram per litre.
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Twenty-two drains carrying domestic wastewater and industrial effluent fall into the Yamuna between Wazirabad and Okhla. Though the 22-km stretch is less than 2% of the river length, it accounts for about 80 percent of the pollution in the river.
While the installation and upgradation of sewage treatment plants (STPs), trapping of sewage flowing in the drains and effective septage management will definitely bring improvement in the river water quality, availability of freshwater is critical for the river to ever reach bathing standards, the erstwhile Yamuna Monitoring had mentioned in a report submitted to the National Green Tribunal in 2020.
"Delhi does not have enough water downstream the Wazirabad Barrage to maintain environmental flow in the river. The solution is we treat all the wastewater to new standards (BOD and TSS less than 10 mg per litre) and clean it further using in-situ bioremediation techniques like constructed wetland systems to achieve a BOD level of 3 milligram per litre and dissolved oxygen greater than 5 milligram per litre," noted botanist and environment expert C.R. Babu said.
In-situ bioremediation techniques involve treatment at the site using aquatic plants or microbial remediation methods. Such systems take less time to become operational, are easy to operate, and require less energy as compared to conventional treatment technologies.
Some common in-situ treatment systems are microbial bioremediation, phytoremediation, constructed wetland system and root zone treatment. Adequate space and appropriate flow are general requirements for adoption of these technologies.
Also read: No dirty water will flow into Yamuna by December-end: NMCG official
"Dissolved oxygen is the most fundamental parameter in water. It is critical to have a biological system in the river. If we can achieve a DO level of five milligram per litre or more, it will improve biodiversity in the water channel which will further remove pollutants," he said, adding the Yamuna can be rejuvenated by 2025. Eminent environmentalist and convener of Yamuna Jiye Abhiyan Manoj Misra said cleaning the Yamuna to bathing standards within the stipulated time seems less likely going by the track record of agencies like the Delhi Jal Board. "But it can be done if you set your benchmark high and think of achieving the impossible," he said.
Besides rehabilitating sewage treatment plants, equal attention should be given to unauthorised industrial activity. Industrial effluent is far worse than sewage, Mr. Misra said.
The government should conduct door-to-door surveys to identify water polluting industries in unauthorised areas and shut them down, Mr. Misra said.
Delhi generates around 770 million gallons a day (MGD) of wastewater. The 34 STPs located at 20 locations across Delhi can treat up to 620 MGD of sewage and have been utilising around 90 percent of their capacity. The rest of the untreated sewage falls into the river directly. Government data shows that only eight out of the 34 operational STPs in the capital meet the prescribed standards for wastewater (BOD and TSS less than 10 mg per litre). Together, they can treat 150 million gallons of wastewater a day.
According to the city government's Outcome Budget, 29% of the sewage generated in Delhi in 2021-22 fell into the Yamuna untreated. It was 28% in 2019-20 and 26% in 2020-21.
The Delhi Jal Board is upgrading and rehabilitating the existing STPs to be able to meet the prescribed norms and reduce the pollution load in the Yamuna. However, several projects have been delayed due to the COVID-19 pandemic, air pollution-related construction ban, and delay in land allotment and tree cutting permissions.
Similarly, permission to lay sewer networks in 161 of the 1799 unauthorised colonies in Delhi is still awaited. "A major reason for the delay in the rehabilitation and upgradation of STPs was an old technique which required construction of new tanks. Since the DJB did not get land and permission to cut trees for a long time, the construction work got delayed," an expert working with the Delhi government said.
"Now, we are using a new technology to upgrade the remaining STPs. The new method does not involve any construction work and there is no land or tree cutting permission required. Only the existing infrastructure is being upgraded resulting in a condensed timeline," the official said.
Joint tenders are being floated for upgradation of STPs and increasing their capacity, and 9 to 12 months are being allotted to the agencies concerned to complete the work, he said, adding, "So, we have ample time to complete the remaining work before 2025".
