Delhi government planning 16 ‘natural STPs’ to treat sewage entering Yamuna
The natural sewage treatment plant (STP) comprises of a sedimentation tank where the sewage is allowed to stand for the total suspended solids to settle down. Water is then passed through four chambers and multiple compartments, which have beds of pebbles of various sizes. This stage filters the sewage.Updated: Feb 12, 2019 13:30 IST
Buoyed by the success of a ‘natural sewage treatment plant (STP)’, the state government is planning at least 16 more such units to treat sewage flowing into the Yamuna.
The natural STP in the heart of Bawana industrial area was installed in July last year. It uses natural material such as pebbles and aquatic plants to clean sewage flowing through the Ghoga drain that starts from the Ghoga village and joins the Bawana escape drain.
At least 10 lakh litres of sewage is treated every day this way.
“The results have been very encouraging. The Biological Oxygen Demand (BOD), which is a measure of organic pollution, has come down from more than 300 to around 30 – 35. Other pollutants such as Total Suspended Solids (TSS) and Ammonical Nitrogen have also dropped drastically,” said a senior official in-charge of three districts.
According to new central pollution control board (CPCB) guidelines, the maximum BOD level should not exceed 20mg/l. Old STPs of Delhi Jal Board(DJB) had BOD level of 30mg/l, while the latest ones claimed to bring down the level to 10mg/l.
“Such natural STPs could go a long way. Natural treatment must be resorted to for better and sustainable results since maintenance efforts and costs are minimal. But there is no need to concretise drains. Natural drains could be treated as well with such natural materials,” said Manoj Misra, convener, Yamuna Jiye Abhiyan.
The STP, which is around 300m long and around 5m wide with concrete walls, comprises of a sedimentation tank where the sewage is allowed to stand for the total suspended solids to settle down. Water is then passed through four chambers and multiple compartments, which have beds of pebbles of various sizes. This stage filters the sewage.
At least four species of fastgrowing aquatic plants feed on the organic matter in the water.
“What goes into the STP is black-coloured highly polluted sewage water. And what comes out is clean water with a reduced level of BOD. The water isn’t be potable though,” said a senior irrigation and flood control department (I&FC) official.
Engineers are now planning to add another section to the STP — activated charcoal.
“According to new standards, STPs built after June 2019 in a metro city is permitted to have a maximum BOD level of 20mg/l. While we have already brought it down to 30mg/l, the activated charcoal section could bring it down to 10mg/l,” said an engineer of the I&FC.
Water treated in the Bawana project is routed back into the Bawana escape drain. In the future, the engineer said, they could route it to a nearby water body from where it could be used for horticulture or recharging ground water. “We will float tenders soon to get Request for Proposal from consultants to come up with at least 16 such plants for as many drains,” said the I&FC official.
NGT panel report
While 22 drains pour into the Yamuna, 11 have been trapped for water treatment by the Delhi government.
A recent study by the Delhi Technological University on behalf of an NGT-appointed panel, however, has revealed that these 11 stormwater drains still carry sewage and little has been done to stop it from flowing into the drains.
“Out of the 40 STPs with an installed capacity of 607 MGD only 34 are reported to be functioning some with capacity utilisation as low as 14%,” read the report submitted to the NGT.
“No new large-sized STPs need be created in Delhi. DJB must ensure that its present STPs work to their best capacity and efficiency,” said Manoj Misra.
A DJB official said that even though some plants are not running at full capacity, the water quality standards are being maintained.
The NGT-committee has asked the Delhi Jal Board to come up with a plan for better capacity utilisation of the plants.
“Even in areas where DJB has provided sewer lines, not all households have been connected to them . The sewage from them still flows down the stormwater drains. DJB has also made some policy level changes so that these households could be connected to the sewer lines. This would help the STPs to get more sewer and run on full capacity,” said a senior DJB official.
Vijay Dev, chief secretary of Delhi held a meeting with the panel members on Saturday and directed the Delhi Jal Board to ensure that all its STPs operate properly to meet the prescribed standards, deadlines given for its various projects are met and there is no leakage of waste water from the sewerage system to the drains.