Sunday, August 6, 2017

Mahalakshmi Grey Water Treatment System Case Study

On 20 July 2017, we visited the site of a grey water treatment system in HSR Sector 5 near Agara Lake in Bangalore. The family of four consumes only about 12 KL of water per month. This water is provided by a combination of Kaveri water, a borewell, stored rainwater, and grey water.  They save about 300 litres of water each day by treating and reusing grey water for gardening.

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GWT System Details
The system at Mahalakshmi's home was installed in 2011 and currently treats about 300 litres of water. At the time of installation, the system cost approximately Rs 80,000 to install, including civil work. Because the system was installed when the house was built, the family is not able to convey any ‘savings’ as such. But they spend very little on water compared to other people.

The GWT system currently treats water from the washing machine and bathrooms. The family uses organic/mild detergents and soaps including Amway products, Genteel, and handmade bath soaps which are easier on the GWT system.

The system consists of the following components:
Component
Dimensions
Notes
Baffle Tank
2’ x 2’ x 2’ with 2 baffles
  • Not cleaned so far
Reed Bed
22.5’ x 2’ x 3’ with 18” of gravel
  • Very few reeds and a few weeds
    • Reeds free from Agara Lake
  • Reeds die when the system dries out - such as when family goes out of town for an extended period
    • Have been replaced 3 times
Polishing Pond
3’ dia. x 13’ depth
  • Round with a metal mesh cover

Aside from the reeds dying when the system dries out, they have not experienced any other problems.

The treated water was tested and gave the following results:
TDS: 792 ppm
pH: 8.2
H2S: No coliform bacteria

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Water Use Breakdown

The family of four uses about 12 KL of water each month. The breakdown of each water source can be seen in the table below.


Water Source
Kaveri Connection
  • When used, the water bill is Rs 300 per month, otherwise it is lower
  • Never used for gardening
Borewell
  • 504 feet deep
  • Used to top up the grey water
    • In dry months, the borewell pump runs every day for 10 minutes
  • Poor quality - high in iron
    • Not used for domestic purposes
    • TDS: 1340 ppm
    • pH: 6.9
Rainwater
  • Harvested in a 30 KL sump
    • Available for use until March every year
  • Used for all domestic purposes
  • Surface runoff goes into a recharge well of 3’ x 6’
  • System was installed in 2011
Grey Water
  • Treated in a planted gravel bed
  • Used only for gardening
  • System was installed in 2011


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