Lead (Pb) removal at low cost, primitive island
We're providing RWH (rainwater harvest systems) on a limestone island in Indonesia, very primitive, virtually no machinery, so hard to do boreholes or shallow wells. The RWH method has been going well for local NGO for years.
However, lead (Pb) is over 20x the 0.5 standard, both in the rainwater (sample taken from stone and cement mortared tanks) as well as commercial tanker trucks that pump from deep wells.
So we need a low cost simple way to remove the lead. I'm aware that some ceramic filters with silver ion also have activated charcoal and claim lead removal. And there are some other materials that adsorb lead, even cilantro (Science Daily article), though I'm not sure we want to force ppl to drink cilantro-flavored water all the time. ;-) Can you provide some careful studies of low cost simple methods for lead removal? Perhaps comparing the alternatives, pros and cons? Thanks, Stew
I agree with Harriette that a preventive measure is preferable to treatment. It is very likely to be more cost-effective and sustainable. Lead can be removed through distillation and certain filters but that isn't going to be cheap or easy.
In the meantime while you are searching for the source of the lead (and removing/replacing it if possible), first flush diverters might help in reducing some of the pollution entering storage. Metals also tend to sink (as evidenced by high concentrations of metal often found in the sludge of RWH tanks), so encourage people to draw water from the top if they aren't already.
Something stuck in my mind about bone char - have a surf around looking for 'removal of lead from water crushed bone filters' and you will find a lot of sites claiming this to be true. Certainly I recall someone I met testing crushed bone as a way to remove fluoride and it seems bone char will do the same. Calcine filters are also mentioned as are carbon, ion exchange resins and activated alumina. I recall slow sand filters also being effective at removing lead from water through adsorption - removal is supported by a National Drinking Water Clearing House fact sheet. Other webpages state that sand filters cannot cope with heavy metals or other excessive pollutants so it may be a question of intensity. You would need to research this more thoroughly.
The CDC has a nice webpage on Domestic Slow Sand Filters titled The Safe Water System at www.cdc.gov/safewater/sand-filtration.html Household Slow Sand Filtration is a good approach to take in any case if using rainwater.
Fascinating that you are doing this on a limestone island - lots of references to using limestone-based granules to effectively remove arsenic, cadmium and lead from water. On sdstate.ebu website there is a pdf titled Development of an Agglomeration Process to Increase the Efficiency of Limestone Based Material to Remove Metals from Drinking Water. Google that title followed by filetype:pdf and you will find it.
There is also a paper on the digitalcommons.wku.edu website titled "reducing lead and selenium from drinking water using limestone-based material" that shows very strong results using limestone for lead removal.
If you can find the source of contamination then great problem solved! If not then the answer may lie below your feet ... :-)
All the best with solving the problem,
I too think determination of the source may be the most economic solution - is there definitely no lead flashing on the roof?
As for testing the other materials, yes I'd say that leaving a sample of each in some rapidly mixed demin water at the same pH as your rain for a similar time period should be as likely to dissolve lead as the rain would. Similarly if you have some available roofing you could test that too - I understand that the zinc chloride used in electroplating can contain lead.
If you concluded that any of these were the source, then I would imagine you would be better replacing them (or lining to stop contact with the water) than trying to subsequently remove the lead.
If it was to be atmospheric lead, the most likely source that springs to my mind would be leaded petrol - is that still used in the area? Since lead is so heavy it isn't likely to hang around in the atmosphere long, so you would expect the source to be fairly close - is the site near a main road or other source of lead?
From there, if it was atmospheric lead, the question would be if it is settling out on the roofs and then being caught up in the first flush, or is the rain stripping the lead from the atmosphere directly. If the former then, as Jeremy suggests, a first flush system is likely to be your best option. My first investigation would be lead analysis of first flush vs subsequent flow.
In terms of treatment technologies, pH correction & coagulation is normally used for lead removal, although this is likely to be too complex for your situation. Orthophosphoric acid is very commonly used for plumbosolvency control, but really removal of the source would be the preferred solution.
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