Lalbagh has 240 acres of land, almost at the center of the city. This was started in the year 1760 by Hyder Ali as a private garden of 40 acres which eventually expanded to accommodate approximately 1,854 species of flora including various ornamental plants. Glass house, aquarium, sidewalks, nursery and many other attractions lure the visitors.
The park requires approximately 2.1-2.2 million liters of water daily, hence when there is no rain, artificial watering is a must. This could be problematic too, as the water supply in the city is dwindling. A 20-acre tank, nine bore wells (sparing three non-functional old wells) plus BWSSB water can meet only one-third of the demand.
To meet the remaining two-third of the demand, they have intelligently setup a tertiary sewage treatment plant with extended aeration, inside the park. It traps domestic sewage from surrounding areas to treat, store and use for watering the park.
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
Scenes from Lalbagh tertiary treatment plant. Pic courtesy: Biome
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Here’s how the treatment plant treats the sewage:
- First it mines 1.5 MLD of raw and completely free sewage from an 8 MLD line.
- Primary treatment: Removal of floating solids and heavy solids. The heavier organic materials like grit, gravel, sands etc are removed by sedimentation process in a settling tank. This is passed through a detention tank to settle the inorganic matters. By this time almost 35% of the BOD (biochemical oxygen demand) and 60-66% of SS (Suspended solids) are removed.
- Secondary treatment: Removal of dissolved and suspended biological matter using aerobic treatment. The fundamental theory is to take the help of microorganisms to convert the organic matter in waste water, in the presence of oxygen. As the end product, settable flocculent (made up of small particles that have been aggregated together) is obtained with the release of gases like CO2, H2O and NH3, alongwith the intended 1.5 MLD clean water.
- Tertiary treatment: At this step, the treated water from secondary treatment is filtered and disinfected with UV rays. The objective is to improve the effluent quality before it is discharged to sensitive or fragile ecosystem.
Some data on the cost of the plant and quality of water:
Setup cost: Rs 4 crore in 2004/2005.
Running cost: Rs 9/- per KL
Electricity cost: About Rs 1.2 lakhs per month.
Area allocated: 2 acre plot with a foot print of 1.2 acres.
Number of staff: 15, including a STP plant manager and a chemist who monitors water quality.
Quality of water: BOD < 5.
Usage: Gardening and excess water is pumped to Lalbagh lake.
Many lessons to learn from here!
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