Grass on the premises of Chennai Metrowater's sewage treatment plant (STP) in Koyambedu caught fire on Wednesday, sending out a billowing cloud of smoke.

Residents staying behind the Chennai Mofussil bus terminus said the flames were visible for some hours in the afternoon before they were put out by a fire tender.

Metrowater sources said the grass on an acre of unused space in the STP campus caught fire, possibly because of a carelessly disposed cigarette. The STP campus is spread over 20 acres. There are plans to establish another STP with a 120 million litres a day capacity there.

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