Iron level reduction
.Am treating water with iron levels > 4mg/l and need to reduce it to < 0.3mg/l.Are there ways of reducing iron levels in drinking water without using an ion exchange system.
We are passing this on to someone who will provide a more comprehensive answer but in the meantime there are the following documents which you may find useful.
There is also this work done at Cranfield University and there are a number of these in operation in Uganda as indicated by the link below.
I was talking to a colleague about this and he has indicated that it it is very important to verify what the source of the iron actually is. What is the source of your water? If it is groundwater, how is your borehole cased, what materials are in use for your rising main etc. There is some evidence from Uganda that where the water is slightly acidic and where the casing or rising mains are galvanised iron, these are corroding and causing iron contamination and that the original groundwater is not contaminated at all.
I presume you want to reduce the iron levels to below 0.3mg/l for drinking water purposes. The standard method of iron removal is by oxidation of the iron (by addition of chemicals or aeration) followed by filtration through a sand filter. Alternatively iron can be removed using a biological filter. Peter Hartmann has written an excellent SKAT Working Paper on Water Supply and Environmental Sanitation titled ‘Iron & Manganese Removal: Simple Methods for Drinking Water’. You can access it on line at this link (it’s 3.6MB of download to beware!) http://www.skat.ch/publications/prarticle.2005-09-29.5069774463/prarticle.2006-11-02.5180575226/skatpublication.2005-10-27.3771055461/filelink text The paper gives some good case studies of different systems used in Sri Lanka, Burkina Faso, Ghana, Argentina, South Africa and Uganda with pertinent technical detail and contact numbers if you want to get more information.
It would be useful to know what treatment you currently have and what form your iron is in.
If your iron is already oxidised [ferric form, Fe3+, iron(III), rust] then pretty much any type of filtration adequate for water treatment should take it out.
If your iron is not oxidised [ferrous form, Fe2+ iron(II)] then pretty much any oxidant (certainly chlorine and sometimes even aeration) should oxidise it to Fe3+ at which point it can be removed by filtration as mentioned above.
Since you mention that you are 'treating water' we'll assume for now that you are disinfecting with an oxidant, most probably some form of chlorine. If you already have some form of filtration, moving part of your chlorine dose upstream of the filtration should oxidise your iron such that it is removed by the filters.
This is not a waste of chlorine, as the iron will currently be passing through your filter and consuming the chlorine after filtration (once it is too late and the ferrous iron is going into supply). So you should end up using not that much more chlorine, but solving your iron problem. If your iron is not oxidised by your point of primary disinfection, there is currently a risk that it is consuming too much chlorine hence leaving you with no residual and inadequate disinfection in any case.
One word of warning however is that if you are using biological filtration (like slow sand) or a non-chlorine tolerant membrane you need to be very careful that your upstream chlorine dose does not cause problems there.
Another word of warning is that if your filter was there to remove organics prior to chlorination, bringing the chlorine dose upstream could increase disinfection byproduct formation (THM's, etc.). If this is the case, you probably want two sets of filtration, with the first taking out the organics, then the mid-chlorine dose, then the second filters for the iron removal, and then your primary disinfection and residual chlorination. And remember that the THMs do have an adverse health affect, whereas within reason the iron issue is only aesthetic.
Another potential issue is Manganese. Manganese is often associated with iron. It is however much harder to oxidise. That means it needs a stronger oxidant, a higher oxidant concentration or longer time for oxidation. Sometimes even chlorine isn't enough. The good thing about manganese removal however is that it is autocatalytic - so the presence the oxidised form of manganese catalyses its own oxidation. You can therefore either allow manganese to coat your filter sand to aid removal of iron and manganese or kickstart the process by using manganese greensand.
Naturally, you probably want to formally engage a process engineer before rearranging your unit processes, but hopefully this gives you an idea of what is theoretically possible.
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