CHENNAI: Three of the 13 lakes identified by Metro Water as additional drinking water sources for the city have been set aside for bio-remediation as they are highly polluted. Dumping of industrial waste and sewage, over the last 20 years, have rendered water in Korattur, Ayapakkam and Thiruneermalai lakes unfit for consumption, as per tests done by the agency.
Important parameters that decide potability of water like turbidity, pH and total dissolved solids (TDS) levels are above permissible levels in these lakes. While solids are between 150-350 mg/l in 10 other lakes, these three water bodies have levels above 1000 mg/l. In terms of chemical and biological quality, all three lakes have very low values and are not feasible for treatment.
Officials said if Korattur and Ayapakkam lakes are bio-remediated and protected from pollution, the combined supply from both can be 8,000 MLD to the city. Officials said the present condition is mainly due to constant discharge of chemical waste and sludge from heavy polluting industries and tanneries in and around Korattur and Ambattur.
“Thankfully, the channel from Korattur to Retteri lake has been completely blocked by encroachments. Because of this, polluted water from Korattur does not come to Retteri. If it does, we will not be able to draw 10 MLD daily from Retteri,” an official said. As Korattur and Ayapakkam lakes fall within corporation limits and can supply water to surrounding localities of Ambattur, Avadi and Pattabiram, they have been chosen first for bio-remediation.
Officials said the board has given its approval to start with soil and water tests once PWD finishes desilting and desludging the lakes. “First chemical sludge needs to be removed. Next desilting has to be done. Later, soil quality will be checked and once water starts percolating in the lake after rain, quality will be checked. This is the ideal time for PWD to start with the basic procedure of desilting as both lakes do not have water,” said a senior official.
Locals and residents at Thiruneermalai allege that large quantities of chemical waste from electroplating industries and tanneries find their way into the lake. “Both private and government industries are notorious for dumping their untreated effluents into Adyar river and Thiruneermalai lake. This has been happening since they were opened. A month ago, I saw some lorries discharging a dark purple colour liquid into the lake” said Pughal V, a local activist.
| Lake | pH | Turbidity | TDS(mg/l) | quantity (MLD) |
| Korattur | 7.7 | 31 | 4156 | 4644 |
| Ayapakkam | 8.2 | 9.4 | 1112 | 3256 |
| Thiruneermalai | 7.8 | 14.6 | 1776 | 849 |
| Acceptable levels | (6.5-8.5) | (1-5) | (500-2000) |