We work on Watershed Development. Soak pit is an important treatment to filter and percolate wastewater (from kitchen, bathroom). In the terrain with black cotton soil and hard rock, water doesn't percolate. In stead it stagnates on ground. Soak pits are also not possible where houses are densely placed, where there is concretization or where there is underground gutter lines.
In such scenarios, what is an alternative treatment to soak pits? Is there any working model for such treatment?
I'm not sure what climate you're working in, but you may be able to alter the soak pit design to allow for the majority of the water entering the soak pit to evaporate instead of infiltrating. For example, if you remove the top capping layer and replace it with larger aggregate stone or porous pavement instead of packed soil, as much as half of the water entering the pit may evaporate in between uses. This is not a good solution for cold-humid climates, but could be used in warm-humid or cold-dry locations. If the soak pit is still overflowing, you could consider putting in planted swales or tree boxes instead. The vegetation will increase the amount of water that evaporates to atmosphere.
In densely populated areas, you might be able to use a barrel-sized sand filter at each house to "pre-treat" water before it exits onto the street. This won't be a perfect solultion, but it should at least prevent raw sewage from being on the road/walkways.
Hello! Nikhil,
In the places where you are unable to make soak pits to percolate water then the option left, in my opinion, will be the evaporation of the water by making of a small tank of 250 gauze plastic sheets. I have used such plastic sheets in those fish ponds which were leeching. I was successful in using plastic sheets as ponds.
Dear Caitlin and Rakesh,
Thank you for your prompt answer. Both the answers suggest evaporation is better method to percolation in such scenarios and I tend to agree. It gives rise to a couple of questions in my mind:
1. Will the method of evaporation work in 4 monsoon months where rainfall is concentrated in India?
2. Is there any working model of the techniques you have suggested? A diagram or a video with specifications of evaporation pit?
Thank you again!
What is the volume of water you are trying to tackle?? You want to just dispose of the grey water through whatever the means including evaporation or you want to better utilize the same by recharging groundwater through proper filtration?? You may try to make use of existing wells for recharging the grey water after proper treatment or re-cycling.
Dear N B Narasimha Prasad Sir,
The volume of water is equivalent to water use in a single kitchen and single bathroom for individual soak pits. The volume of water is upto water use in 10 kitchens and 10 bathrooms for community / group soak pits. Please note that it doesn't include toilet water.
We want to better utilize this water by recharging. However, it's difficult in the terrains with hard rock and black cotton soil.
Thank you.
Hi Nikhil,
There have already been some good suggestions. Evapotranspiration Absorption (ETA) beds seems to be the way forward. Attached is a link to guidelines on design of these systems to shed rainfall. Not sure about 4 months of monsoon rain but hope this helps.
Regards
www.waternsw.com.au/__data/.../Section-11-Evapotranspiration-Absorption-Beds.pdf
Evaporation is not the solution, as I understand the grey water is to be better utilized during the water scarce period. The waste water from toilet is categorized as dark water. Only the waste water from kitchen and bathroom (categorized as GREY water) are suggested for recycling and reuse. In this case the grey water can be filtered and treated appropriately and there after collected in a pond like structure for using the water in summer period for cleaning and gardening purposes.
You could also try using the FILTER method (Jayawardane et al. 2003 pp 249-275. In Urban waste management in Australasia-Pacific region. Science Publishing Inc. Emfield, New Hampshire, USA. Urban; Jayawardane et al. 2001, Australian J of Soil Res. 39: 1247-1258). This uses a intense drainage network to collect filtered water and soil/plants to remove nutrients etc.
Thanks Freeman. Much better to give a holistic overview on sustainable urban development rather than specific recommendation. I also sourced the document (Tools for Urban Water Management and adaptation to Climate Change) below following your lead.
https://publications.csiro.au/rpr/download?pid=csiro:EP128117&dsid=DS7
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