Sunday, August 6, 2017

Ravi and Rekha Iyer Grey Water Treatment System Case Study


On 20 July 2017, we visited the site of a grey water treatment (GWT) system in a layout off of Sarjapur Road in Bangalore. The family of five consumes approximately 30 KL of water per month. This water is provided by a combination of the layout sump, stored rainwater, and grey water.  Every month they save approximately 250 litres of water each day by treating and reusing grey water. 

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GWT System Details
This system was installed at the home of Ravi and Rekha in 2013. At the time of installation, the total cost was about Rs 40,000 including the civil work. Currently, 250 litres are being treated by the system.

The GWT system currently treats water from the washing machine and bathrooms. The family uses organic/mild detergents and soaps including detergents/dishwash from Eco Store and handmade bath soaps which are easier on the GWT system. They made the switch to these products because the water would smell when they used chemical detergents - there is no smell following the switch to the new products.

As mentioned, there were problems with smell and the water turning black which was solved by changing the detergents. It should also be noted that the inspection/aeration ports and the openings of the pipes into and out of the tank are covered with mosquito nets to prevent reptiles, insects, leaves, etc from entering.

The system consists of the following components:
Component
Dimensions
Notes
Baffle Tank
3’ x 2’ x 2’ with 2 baffles
  • Includes a grease trap and settlement chamber
  • Not cleaned so far
Reed Bed
6’ x 4’ x 3’ with 18” of gravel
  • Full of Chinese umbrella
    • Need regular trimming
Intermediate Maintenance Chamber
1’ x 1’ x 1’
  • RO reject water and non-soap wash water from kitchen sink passes through this into the polishing pond
Polishing Pond/ Storage Tank
3’ dia. x 6’ depth
  • Round with a plastic cover and removable mosquito net
  • Previously cleaned regularly, now only pipes are cleaned
  • Created by lowering a 700-1000 litre HDPE tank into the ground

The treated water was tested and gave the following results:
TDS: 1660 ppm
pH: 7.7
H2S: Black after 48 hours - presence of coliform bacteria

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Earlier they would be very careful about watering the garden so as not to use up too much of the tanker water, but after the GWT system was set up, they are able to water the garden well.


Water Source Overview

The family of four uses about 30 KL of water each month. The breakdown of each water source can be seen in the table below.


Water Source
Layout Sump
  • Piped to houses and is stored in a 15 KL sump, then pumped to an OHT
  • Used for all domestic purposes and some is used in the garden, especially in the dry season
  • Billed every quarter; average Rs 10,000 per quarter
Rainwater
  • Harvested into the 15 KL sump which is mixed with layout water
  • Gutters on sloping roofs are still to be attached
    • Current rooftop runoff is very little
  • Surface runoff goes into a recharge wells on the road
  • System was installed in 2013
Grey Water
  • Treated in a planted gravel bed
  • Used only for gardening every alternate day
  • In dry season, it gets completely emptied and needs to be supplemented with layout water
  • System was installed in 2013

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