The total coliform count, indicating faecal contamination, has exceeded the maximum permissible limits by 160 and 96 times respectively in Perandoor and Edappally canals.
The alarming rise in the presence of coliform bacteria came to light during tests conducted by the State Pollution Control Board (PCB) from December 9 to December 23.
The total coliform count in a sample collected from Monitoring Station-II in Perandoor canal was 4,00,000 cfu/100 ml. According to the Central Pollution Control Board, the maximum permissible limit of faecal coliform in water used for organised outdoor bathing is 2,500 cfu/100 ml, while the desirable value is only 500 cfu/100 ml.
The spike in coliform presence shows the indiscriminate discharge of septage into the two major canals. The board attributed the rise in coliform levels to the discharge of untreated sewage from households and commercial establishments into the canals.
The microbiological examination of samples collected from another collection point in Perandoor canal found a total coliform count of 3,50,000 cfu/100 ml. It was nearly 140 times higher than the maximum permissible limit. The coliform presence in samples collected from Station-1 of the Edappally canal was 2,00,000 cfu/100 ml, which was nearly 80 times higher than the permissible limit. At Station-II, samples showed that coliform presence was 2,40,000 cfu/100 ml, nearly 96 times higher than the permissible limit.
The Biological Oxygen Demand (BOD), a proxy for organic pollution, was higher than the ideal limit of 3 mg/l prescribed by the Central Pollution Control Board in samples collected from both the canals. The higher levels of BOD indicated the deteriorating ecological condition of the waterbodies. The board considers a BOD less than 3 mg/l an indicator of a healthy river stream.
The BOD at Station-II in Perandoor canal was 35 mg/l, while the corresponding figure for samples collected from another spot was 14.5 mg/l. The BOD levels at Station-1 and Station-II in Edappally canal were 14.5 mg/l and 14.7 mg/l respectively.
The Chemical Oxygen Demand (COD), a measurement of the oxygen-depletion capacity of a water sample contaminated with organic waste matter, was 104 mg/l and 32 mg/l in Station-II and another collection point respectively in Perandoor canal. The corresponding figures at Station-1 and Station-II in Edappally thodu were 40 mg/l and 36 mg/l respectively.
