New user?
0

Rehabilitating ponds

I am working for SRSA as a WASH technical advisor assisting Save the Children and UNICEF with treatment plants and rehabilitation of ponds

A lot of agencies are adding lime to rehabilitated ponds but nobody can give a scientific explanation of the benefits of it. I have been around in Labutta and Bogale Townships and discussed it with all stakeholders doing WASH. There are some that adds because villagers wants them to, there are other that don't. We are many watsans that do not see the point in adding lime, as the only obtainable result is an increase of the pH. Do you know if there are other benefits? Thank you very much!

Regards,

Rolando

edit retag flag offensive close merge delete

6 Answers

Sort by » oldest newest most liked
0

Can you clarify if these ponds are for Wastewater treatment? I guess they are...otherwise why else would they be rehabilitated - possible water sources? Also, what are they contaminated with - seawater? Bodies? How much lime are people adding?

Regards,

Mark

edit flag offensive delete publish link more
0
  1. The ponds are not for Wastewater treatment
  2. The ponds are actually rainwater catchments, all villages have several of them, and they are used both for water drinking purposes and for agriculture during the dry season.
  3. Actually both, bodies and seawater. However the most significant problem is salinity as the cyclone brought a tidal way that flooded thousands of drinking water ponds.
  4. I can't say exactly the right quantity, but the average pond size is: 33m x 33m x 2.5 m and 66m x 66m x 2.5 m Then the pond is totally dewatered and lime is spread forming a thin layer.

Regards,

Rolando

edit flag offensive delete publish link more
0
  1. The ponds are not for Wastewater treatment
  2. The ponds are actually rainwater catchments, all villages have several of them, and they are used both for water drinking purposes and for agriculture during the dry season.
  3. Actually both, bodies and seawater. However the most significant problem is salinity as the cyclone brought a tidal way that flooded thousands of drinking water ponds.
  4. I can't say exactly the right quantity, but the average pond size is: 33m x 33m x 2.5 m and 66m x 66m x 2.5 m Then the pond is totally dewatered and lime is spread forming a thin layer.

Regards, Jeff

edit flag offensive delete publish link more
0

Georg Smethurst in Basic Water Treatment only mentions using lime to adjust pH to:

  1. Improve coagulation
  2. Prevent corrosion

It might be interesting to test for pH to see if there is a potential problem with 2 above – my assumption that coagulation is not used. Regards,

Tim

edit flag offensive delete publish link more
0

The following University of Florida paper sets out the basics of adding lime to fish ponds to control pH. Lime may need to be added on a regular basis to counteract the influence of acidic soils. http://edis.ifas.ufl.edu/FA028 However the use of lime may be even more critical after storm damage if the fish pond dried out due to the walls being breached. This is because some soils can generate large amounts of acid when exposed to the air.

There was a problem after the 2004 Indian Ocean Tsunami that raw acid sulphate soils were exposed to the air for several months and generated large amounts of sulphuric acid.

The Australian ACIAR was very involved in pond rehabilitation after the 2004 tsunami:

http://www.bees.unsw.edu.au/school/staff/sammut/sammut_media3.pdf.

The ACIAR site is at http://www.aciar.gov.au FAO also have some material on aquaculture pond rehabilitation.

Regards, John

edit flag offensive delete publish link more
0

Adding lime (Calcium Hydroxide) is a water softening process, and will remove carbonate (limestone or chalk aquifers) and non-carbonate hardness (normally from water passing through clay soils containing sulphate. It leads to the precipitation of calcium carbonate (1:1 moles), magnesium carbonate (2:1 moles) and, eventually, bicarbonate. Normally sodium carbonate (soda or soda ash) is added to remove the magnesium hydroxide, which is soluble in cold water (less soluble in hot water).

The addition of lime will raise the pH of the water, which will provide a disinfection action of itself. The WHO Water Guidelines state (table 7.6, pg 139) that up to 99% of Bacteria, 99.9% of viruses and 99% of protozoa present may be removed by the addition of lime through inactivation at high pH and removal from the water column by precipitative hardness. It should be noted that if chlorine is being used as a further disinfectant then it becomes progressively less effective as the pH rises, and should be generally no higher than 8.

It is difficult to tell why villagers would want the process carried out; I would be inclined to give them what they want as there are water quality benefits involved. I would also be inclined to talk to the villagers about why they think lime is required. It may be just because it has been carried out traditionally. In an emergency I would recommend going with what the population trusts, as long as you know it will not have any negative impacts. That way you can be sure that people are not accessing water in sufficient quantities because they are wary about the methods used to provide it. I may also have some benefit in conflict prevention; if you do something new and there is an negative impact, even if unconnected, the local population are likely to blame

Regards,

Cody

edit flag offensive delete publish link more
Login/Signup to Answer
Question Tools
1 follower
Public thread

This thread is public, all members of KnowledgePoint can read this page.

Stats
Asked:
2014-01-20 04:12:52 -0500
Seen:
123 times
Last updated:
Jan 20 '14