Of samples drawn from treated water of sewage treatment plants (STPs) at 25 locations in Delhi last month, treated effluent from STPs at 14 locations, including large ones at Okhla and Keshopur, did not meet the standards for treated effluent prescribed by the Delhi Pollution Control Committee (DPCC). This is as per the DPCC’s analysis report for February, which analysed treated effluent from a total of 31 units.

The standards are applicable for discharge of effluent into sources of water, like the Yamuna where much of the treated water ends up, or land disposal, when some treated effluent is reused for horticulture.

Only samples from STPS at 11 locations, analysed at the DPCC laboratory, met standards prescribed for parameters including total suspended solids (TSS), dissolved phosphates, ammoniacal nitrogen, biochemical oxygen demand (BOD), and chemical oxygen demand (COD).

STPs that did not meet prescribed standards include the one at Okhla, which has an installed capacity of 110 million gallons per day (MGD); Yamuna Vihar Phase 3; and Kondli STP, which has a capacity of 45 MGD.

At the Yamuna Vihar STP, the concentration of total suspended solids was found to be 90 mg/litre, 9 times the prescribed limit of 10 mg/litre. The biochemical oxygen demand was 48 mg/litre, while the prescribed limit is 10 mg/litre. The chemical oxygen demand was 144 mg/litre, nearly three times the limit of 50 mg/litre.

Some plants, like the Rohini STP, were found not meeting the standards for ammoniacal nitrogen, which is produced by the degradation of organic matter. At the plant, the ammoniacal nitrogen level in treated effluent was 6.2 mg/litre, above the prescribed limit of 5 mg/litre.

Projects to upgrade the STPs are in the offing. A senior official of the Delhi government said funds under the National Mission for Clean Ganga would be utilised for some STPs, while others are being funded by the Delhi government.

The tender process is underway for the plants that are being upgraded by the government, he said. Some of these plants were designed for higher parameters at the outlet, and the upgraded plants will help meet the parameters for BOD, TSS and nutrients. “Once some of the new STPs are constructed, some of the old units will be abandoned. STPs at around 20 locations will be upgraded,” he said.

Several STPs have not been meeting standards for months. Analysis of the samples drawn in February last year shows that the Okhla, Keshopur, Coronation pillar and Yamuna Vihar STPs were not meeting standards then too. These plants have also not met the standards in October, November and December last year.

In a status report on rejuvenation of the Yamuna, presented to the Ministry of Jal Shakti last month, the DPCC stated that the Yamuna Vihar, Rithala and Kondli STPs are being upgraded to meet standards prescribed for total suspended solids and biochemical oxygen demand.

Additionally, 16 STPs are to be upgraded to meet TSS and BOD standards at a cost of Rs 2,721 crore. Work is yet to begin. The report states that economically feasible technology is being considered, including the use of ferric chloride to treat water, and increasing aeration by using floating aerators.

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