The Delhi Government has promised to clean the Yamuna to bathing standards by 2025, as the pollution load in the river has increased substantially over the last five years.
The environment department report shows that barring Palla, the annual average level of biological oxygen demand (BOD) increased at every location of water sample collection for testing in the national Capital.  BOD, an important parameter for assessing water quality, is the amount of oxygen required by aerobic microorganisms to decompose organic material present in a water body. BOD levels less than 3 milligram per litre (mg/l) is considered good.
There was no immediate reaction available from the environment department.   The Delhi Pollution Control Committee (DPCC) collects river water samples at Palla, where the Yamuna enters Delhi; Wazirabad, ISBT bridge, ITO bridge, Nizamuddin bridge, Agra Canal at Okhla Barrage, Okhla Barrage and Asgarpur.
The DPCC data showed while there has been no major change in the annual average BOD level at Palla over the last five years (from 2017 to 2022), it has increased from around 3 mg/l to around 9 mg/l at Wazirabad.
The BOD level has risen from around 30 mg/l to 50 mg/l at the ISBT bridge and from 22 mg/l to 55 mg/l at the ITO bridge during the period.
Similarly, the BOD level worsened from 23 mg/l to around 60 mg/l at Nizamuddin bridge, from 26 mg/l to 63 mg/l at Agra Canal at Okhla Barrage, from 26 mg/l to 69 mg/l at Okhla Barrage and from around 30 mg/l to 73 mg/l at Asgarpur, the data showed.
The Yamuna river can be considered fit for bathing if 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 mg/l.
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 two per cent of the river length, it accounts for about 80 per cent of the pollution in the river.   Though a minimum environmental flow is required to clean the river to bathing standards, treating all the domestic wastewater and industrial effluent and further cleaning it using in-situ techniques can help reduce pollutant load significantly, according to eminent environmentalist Manoj Mishra.
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.