Releasing untreated domestic sewage containing high levels of surfactant, a main component of detergents and soaps, into River Noyyal is found to be the prime reason for frothing in the river which is known as the lifeline of Coimbatore.
Examination of water samples collected by the Tamil Nadu Pollution Control Board (TNPCB) from the Noyyal earlier this month showed 0.8 mg/L (milligram per litre) of surfactant in the river as against the normal level of .2 mg/L.
The samples were collected from the river at Pattanam Pudur in the first week of May after incidents of frothing were reported. District Collector Kranthi Kumar Pati, who visited the spot along with TNPCB officials, instructed for an examination of samples.
R. Chandrasekaran, District Environmental Engineer, Coimbatore south, said the water samples were tested in a laboratory at the South India Textile Research Association (Sitra), which is accredited by the National Accreditation Board for Testing and Calibration Laboratories (NABL).
According to the official, surfactant should not be present in the drinking water. In rivers and streams, surfactant presence beyond .2 mg/L is considered high. The tests also showed higher levels of dissolved organic matter, he said.
“Frothing occurs when water containing surfactant falls from a height. This was the reason for the recent frothing in the river where water fell from a height of about 2.5 feet,” said Mr. Chandrasekaran.
The official denied the general allegation that dyeing industries were main contributors of pollution in the Noyyal. “No dyeing units are functioning the banks of Noyyal in Coimbatore… Untreated domestic sewage released into the river is the main source of surfactant. This can be prevented by processing domestic waste water through sewage treatment plants (STPs)”, he said.
Meanwhile, the TNPCB has decided to collect samples from four locations in the river every month and test them to check pollution levels. The samples will be collected from Pattanam Pudur, Podanur, Athupalam and from one location in the upstream near Perur.
K. Mohanraj of Save Coimbatore Wetlands wanted the Coimbatore Corporation to expedite linking of households with the Under Ground Sewerage Scheme and increase the city’s sewage treatment capacity.
The three STPs in the Corporation at Ukkadam, Nanjundapuram and Ondipudur have a total installed capacity to treat 170 million litres per day (MLD).
According to Mr. Mohanraj, about 70% of water used by an individual turned into waste water. Considering 135 litre per capita per day as the benchmark for urban water supply, the wastewater generated by the current population of about 22 lakh people will be 222.75 MLD.
“The present total installed capacity itself is insufficient to treat the waste water generated by the current population in the city. Also, the installed capacity is underutilised. As the population is growing exponentially, the civic body has to give more focus on addressing this huge issue,” he said.