Water quality improved at coastal areas, Mithi river got more polluted during lockdown period: Report
Water quality at major beaches in the city witnessed an improvement during the lockdown. However, the Mithi river was more polluted than in pre-lockdown months and the corresponding period last year. The Maharashtra Pollution Control Board (MPCB) released the water quality analysis of major rivers and coastal areas in and around Mumbai in April on Thursday.
MPCB measured pollution levels using the water quality index (WQI), which provides a single number (grade) on overall water quality that is location and time-specific, and based on specific parameters (see box). While 38 or less is ‘bad to very bad’ or heavily polluted (red), 38-50 is ‘bad’ or polluted (orange); 50-63 is ‘medium to good’ or non-polluted (yellow); and 63-100 is ‘good to excellent’ (green).
The Mithi and Mahim creek, into which the river flows, were the only two listed water bodies in the ‘heavily polluted’ category with pollution levels at 25.7 and 37.4 (red category). Versova, Juhu, Nariman Point, Gateway of India, Malabar Hill, Girgaum Chowpatty, Haji Ali, Shivaji Park Dadar and Worli Sea Face all recorded levels ranging from 51 and 58 (yellow category or non-polluted) in April.
During January and February 2020 as well as in March and April 2019, Mahim creek was in the orange category while Mithi was in the red category.
MPCB said there was an overall reduction in sewage load at marine outfalls. “There was a reduction in untreated domestic sewage coming from large hotels, offices, industries and activities from other establishments that were all shut during the first phase of the lockdown. Also, existing sewage treatment plants (STPs) functioned at optimal capacity along marine outfalls to treat waste efficiently, which was only coming from slums and households,” said YB Sontakke, joint director (water quality), MPCB.
Prior to the lockdown, 2,671 million litres per day (MLD) of domestic waste was being generated in Mumbai of which 2,016 MLD was treated before being released into the sea, according to MPCB. This means 25% of the city’s sewage is entering the sea without any processing. “During the lockdown, total sewage generation fell by 450-500 MLD while the gap in treatment continued to be 25%. However, the daily sewage load entering Mithi was over 300 MLD,” said Sontakke.
He added that water pollution in Mithi River continues to be a serious issue for Mumbai. “Owing to lesser water flow due to less desiliting activity during April, stagnation of water and low dilution led to higher pollution levels,” said Sontakke. “We are checking with the Brihanmumbai Municipal Corporation (BMC) regarding desilting work and progress before monsoon.”
A senior BMC official said, “Owing to lockdown restrictions, there was hardly any desilting work done during April (in the Mithi) but 80% work has now been completed. The May water quality should show an improvement for Mithi.”
An independent expert said MPCB’s findings could be accurate, but the sample collection source needed to be checked. “Coastal water quality during pre-monsoon months is generally poor for Mumbai. The findings show a marked decline biochemical oxygen demand (BOD) — indicating the level of oxygen that aquatic life need for survival — and nitrate levels in coastal waters during April, which fell below safe standards due to less sewage load,” said professor AD Sawant, water quality analyst and member of Supreme Court committee on Mithi River rejuvenation. “The installation of STPs along Mithi River need to be expedited and all desilting activities need to be completed to ensure increased river flow and dilution to curb pollution,” said Sawant.
Meanwhile, the water quality at Ulhas River, a major river providing water to Mumbai metropolitan region also improved to a non-polluted status based on samples collected from six regions along the river. “Apart from a drop in industrial effluents, other activities such as washing of vehicles, jeans washing units, service centres etc. all stopped, improving Ulhas water quality,” said Sontakke. However, other industrial zones like Tarapur MIDC, Rabodi nullah etc. recorded higher levels of pollution.
Fewer water samples were collected during March owing to travel restrictions during the lockdown, while samples for May are being collected and published soon, said Sontakke.