New Delhi Oct 31 PTI On an average 24 out of the 35 sewage treatment plants STP in the national capital did not meet the prescribed standards for wastewater over the last one year according to government dataDelhi generates around 720 million gallons wastewater a day The 35 STPs located at 20 locations across Delhi can treat up to 597 MGD of sewage and have been utilising around 90 percent of their capacityAccording to the Delhi Pollution Control Committee biological oxygen demand BOD total suspended solids TSS and total nitrogen in the treated wastewater should be 10 milligrams per litre or lessChemical oxygen demand COD should be less than 50 mg per litre and ammoniacal nitrogen and phosphate should be belowfive mg per litre and two mg per litre respectivelyBiochemical oxygen demand is the amount of dissolved oxygen used by microorganisms to metabolise organic matter in water High BOD levels mean there is a high level of microorganisms in the water and a high content of organic material that is broken down by the organismsCOD describes the amount of oxygen required to chemically break down pollutantsThe STPs that met the norms the most number of times included Okhla Phase six Dr Sen Nursing Home Nalla Delhi Gate Nalla Phase one Delhi Gate Nalla Phase two Chilla Common Wealth Games Village Nilothi Phase two and Papankalan Phase twoIn October last year teams of the Delhi Pollution Control Authority DPCC collected samples from 33 STPS Of these 23 were found not complying with the standardsTwenty-three in November and 22 in December did not meet the prescribed standardsAccording to government data 25 STPs in January this year 26 in February and 24 in March failed to meet the criteria for wastewater Samples could not be collected for testing in April and May due to the COVID-19 pandemic and the lockdownThe DPCC inspection found that 22 STPs in June 24 in July 26 in August and 26 in September did not meet the standardsAn official said many STPs do not have the technology to clean the wastewater to the updated DPCC standardsThe earlier governments did little to clean the Yamuna The Arvind Kejriwal dispensation has undertaken projects to upgrade these STPs and this will take around three to four years he saidEarlier this year authorities had informed the National Green Tribunal that the upgradation of STPs in Uttar Pradesh Haryana and Delhi to substantially reduce foaming in the Yamuna will take three to five years depending upon the availability of land and funds etcThe presence of phosphates and surfactants in untreated sewage from Delhi Haryana and Uttar Pradesh is a major reason behind frothing in the riverOfficials said the delay in tree cutting permission COVID-19 lockdown financial hardships and migration of labour slowed down the construction and upgradation of four major sewage treatment plants STPs Kondli Rithala Okhla and Coronation Pillar -- in DelhiThese plants will be able to treat 279 MGD wastewater The 70-MGD Coronation Pillar STP is to be completed by November 2021 while the deadline for Kondli Rithala and Okhla STPs is December 2022The construction of Coronation Pillar STP slowed down mainly due to the delay in handing over the site appointment of project management consultant construction ban imposed by Environment Pollution Prevention and Control Authority COVID-19 lockdown and migration of labour etc PTI GVS DV DV