New Delhi, April 20 -- Nine out of 37 sewage treatment plants (STPs) in Delhi are either non-operational or do not meet the water treatment parameters set by the Central Pollution Control Board (CPCB), according to the latest monthly report on STP functioning in the Capital.

The report for March, dated April 13, showed that while seven STPs did not meet prescribed standards, another two were non-operational and undergoing rehabilitation.

Though an improvement from February, when 14 STPs were either non-operational or not meeting parameters, experts raised concerns that the improved STP data does not tally with Yamuna's water quality, which deteriorated in March.

The monthly Yamuna water quality report, also published by DPCC, for March...