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Technologies For Grey Water Management At Public Water Points

            Some GPs have provision for public water supply in the form of hand pumps, stand posts or wells. At all such places, a large quantity of water is wasted. This also needs to be managed properly; else the water from such sources flows onto roads and open spaces and causes inconvenience.
Apart from public water points, some GPs also have public washing places (for cloth washing) and cattle troughs. These places also require some arrangement for managing the waste water. These can be similar to the arrangements for public water points.
Following technologies can be adopted for the above purpose.


1) Reuse in Plantations/Orchards


Like kitchen gardens at home, wastewater from community water sources can be utilized in community plantations and orchards.


Significance of Reuse of Community Wastewater


In villages where public stand posts, hand pumps or wells are provided as a source of water, the wasted water can be channelized and utilized for growing vegetation.


Requirements


  1. Adequate space near the water point; if at all such space is not available in the vicinity, this water can be conveyed to the required distance through a pipeline; and
  2. Silt chamber to settle the solids in the grey water. (refer figure 15)
  3. Secondary silt chamber at the plantation site if it is at a considerable distance from the water point.
  4. Pipeline of required specification to convey the grey water from public water point to the plantation site
  5. Some arrangement at the GP level for management of the system. This task can be assigned either to Self Help Groups (SHGs), youth groups or even to some private entrepreneurs.

Design Considerations


The design of a plantation will differ with every water point. Careful planning is essential. The following factors should be taken into consideration while planning for a plantation.

  1. Space available for plantation
  2. Quantity of grey water
  3. Plant species intended to be grown

Suggested Usage


  1. Vegetable garden for commercial purpose
  2. Orchards (fruit trees) for commercial purpose
  3. Existing park/garden in the village
  4. Roadside trees/other vegetation

Description


The wastewater generated at public water points is generally overflow or spilled water and does not contain impurities such as organic matter, ash or other chemicals. But it invariably contains dirt and mud. Hence, it must be passed through a silt chamber (refer figure 15) so that solids-free water is available for end use. The silt chamber should be constructed near the water point and the solids-free water should then be conveyed through pipes to the plantation site. This will avoid clogging of pipes with dirty water.


Operation and Maintenance


A) Cleaning of the silt chamber should be done weekly/fortnightly or as required; B) Deposition of inert matter/organic matter/salts on the soil surface should be removed after harvesting of crops; and C) In the rainy season, when grey water is not required it should be diverted to some other system to avoid stagnation and vector breeding.


2) Large Leach Pit


If it is not possible to make use of wastewater from community water points in a garden/plantation, it is advisable to construct a large leach pit and soak the wastewater in it.


Description


This is a brick-lined pit constructed at a convenient place near the water point. The design and other parameters of this leach pit will be the same as that of the community leach pit. A silt chamber of a suitable size should be constructed near the water point and all the spilled water should be directed to this chamber. From this chamber, it should be taken to the leach pit through a pipeline.


Essential Components of the System

  1. A well cemented platform around the water point (hand pump, stand post or well) so that all the spilled water can be conveniently collected at one point.
  2. A silt chamber near the water point (see figures 15)
  3. A pipeline (100 mm diameter PVC or SWR pipe) from the silt chamber to the leach pit laid preferably underground but at a shallower depth
  4. A leach pit of specific dimensions

Significance of a Large Size Leach Pit

  • Dry environment: spilled water from the water point is absorbed by this underground structure. The surrounding premises remain dry and clean;
  • Freedom from the mosquito nuisance;
  • Odour-free environment;
  • Recharge of ground water: the wastewater enters the natural ecosystem and finally recharges the ground water;
  • A low-cost option compared to a drain + centralized treatment unit;
  • O&M costs comparatively lower than for the drain + centralized treatment system.

Site Selection

  • The pit should be located at a place provides the necessary gradient for gravity flow of wastewater from the household to the leach pit; and
  • It should be minimum 3-5 m away from the water source.

Design Considerations


  • Shape: preferably circular (cylindrical) to keep costs low,yet durable;
  • Construction: honeycomb masonry in alternate layers to facilitate seepage of water;
  • Bottom of the pit: not to be cemented or concreted also to facilitate seepage of water;
  • Inlet pipe: 75 to 100 mm diameter PVC or SWR pipe, to be connected to the pit keeping 300 mm freeboard; and
  • Volume: Effective volume (volume up to pipe level) should be kept equivalent to double the daily discharge of grey water from the house. e.g. if the discharge of waste water from a public water point is 3000 lit, the effective volume of the said leach pit should be 6 cum to accommodate 6000 lit of grey water (3000 lit x 2 = 6000 lit. One cum of volume accommodates 1000 lit of water.)

Step-by-step Construction


  1. Excavation: dig a pit with the required dimensions
  2. Construction: construct the pit with 225 mm thick brick work with honeycombing in alternate layers. Brick masonry to be done in 1:8 cement mortar
  3. Piping: connect the pipe at a height keeping 300 mm freeboard. The pipe should protrude 100 mm inside the pit
  4. Corbelling: the diameter of the community leach pit is always larger. Hence, the top portion should have corbelling to reduce the diameter of the opening at the top to about 1 m (refer figure 15)
  5. Cover: 50 mm thick RCC cover cast in two halves/ferrocement slabs/flag stone
  6. The cover to be properly sealed to avoid vector entry
  7. The cover to be covered with a soil layer of about 300 mm

Connection with the Water Point


  1. The final outlet from the platform around the water point should be connected to the silt chamber by a 100 mm PVC/ SWR pipe
  2. The silt chamber should be connected to the leach pit by a 100 mm PVC/SWR pipe of a suitable length

Operation and Maintenance


A) Cleaning of the silt chamber should be done weekly/fortnightly or as found essential
B) De-sludging of the leach pit should be done once in a year.