Hyderabad: The unscheduled rain in May are to be blamed for the fresh bout of stink at the Hussainsagar.
Officials said there was is zero discharge of polluted water into the lake, but the sudden rain brought with it water from stormwater drains, chemicals such as phosphorus, sulphur (responsible for the smell of rotten eggs) and nitrate. These chemicals catalyse the growth of algae, along with sunlight. The smell is caused by the presence of algae, live and dead.
A senior HMDA official, an expert in geo-ecology, explained, “The high day temperatures and inflow of nutrients facilitate the growth of algae. Sudden incessant rain flooded the nalas and bring phosphorus, nitrate and sulphur with sewerage. This activates algae growth, along with sunlight.”
He said the life cycle of algae is around 2-4 weeks. When the algae dies, there is putrefaction. The dead algae, if not removed, begins to stink. The official said some fish feed off the algae.
During dry weather, there was zero domestic inflow. The smell will decrease if the oxygen levels increase in the lake, he said. To avoid anaerobic conditions — an aquatic environment with little available oxygen — in the lake the HMDA procured an aerator system. This equipment improves dissolved oxygen levels in the lake water.
An official said the stink was particularly intense this year because the tank was not drained out, unlike last year when some amount of water was removed.
The GHMC irrigation wing in the name of repairing sluices, had let out water through the outlet near Marriot Hotel. This caused water levels to fall by a few feet and the shore line of the tank was seen.
Experts said that the smell intensity was less last year because the distance from the water was more. Since there is no dewatering this year, there is more water and the smell is more intense.
Surprisingly the footfall at all the three parks has not seen a drop due to the smell. The Lumbini, NTR and Sanjeevaiah parks recorded 2.95 lakh visitors in March and 3.15 lakh in April.
