treatment vs. irrigation
Jacky Foo
+++++
treatment vs. irrigation
Submitted by Hanns Pitot on Mon, 23/07/2007 - 22:47.
Dear all,
Just now, I've found the time to go through this very interesting
discussion, and I would like to thank Liaqat Hayat and the other
participants for making it a very interesting reading experience!
A few clarifications: There is waste water treatment using artificial
wetlands, and there is waste water treatment using irrigation methods,
with some form of pretreatment, and there are the plants that are
specifically suited for either one. As I see it, the two haven't been
clearly separated in the discussion. And there is also the combination
of both, CWLs as a pretreatment and irrigation as main treatment.
Concerning plants:
For CWLs with subsurface flow (horizontal or vertical): first of all
the regular reed plant (Phragmites australis or communis), vetiver
grass and canna as mentioned, cat tail, etc...
For waste water irrigation: even if hygienization is provided in the
pretreatment, nonfood crops are recommended (as an additional safety
barrier, and in case of chemical contamination). Water hungry energy
plants should be particularly suited. Examples are Eucalyptus sps. and
sugar cane (energy cane). Fruit trees, like banana, or ornamental
plants (again canna, and many others) are other possibilities.
If I have understood you correctly, Liaqat, you original idea was to
actually go for the combination of the two, and I would like encourage
you to follow this path, as it is making the best use of both water
and nutrients. In that case, the overall setup would be septic tank -
constructed wetland - plots with waste water irrigation. In such a
setup, the role of the treatment in the CWL would actually NOT be to
consume as much nutrients as possible, as these would be preferred in
the irrigation portion. The purpose would be to provide hygienization
and to remove odors.
Constructed wetlands using Phragmites australis for treatment are
designed at 3 m2 (vertical flow) to 5 m2 (horizontal flow) per person-
equivalent in Germany, and I would think that in the tropics, these
numbers can be significantly reduced. And if the CWL is just serving
as a pretreatment for irrigation, I would think areas can be as low a
one m2 per person in a vertical flow setup.
Another point that I would like to mention: You were asking about what
to do with the sludge from the septic tank(s). Did you ever consider
composting toilets? This should prevent a good deal of the sludge
buildup in the septic tanks. It would also save a lot of water and
reduce treatment needs.
Thanks,
Hanns-André
Hanns-André Pitot
Member of the AT-Association
Am Steinacker 42
38723 Seesen
Germany
Tel./Fax: -49-5381-5468
E-mail: hap...@yahoo.com