Removing fine turbidity from spring water in DRC
Hi - one of our gravity fed schemes in DRCongo has very fine turbidity particles, making the water almost milky in appearance. We have tried settling the water, filtering it through m cloths, even force-filtering it through pressure membrane apparatus, but the turbidity remains (around 300 NTU). My only thought for solving this is to use slow sand filtration 9We are not in a position to adopt reverse osmosis in this isolated rural context). Do you concur with this opinion, or have any other ideas?
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3 Answers
Couple of things here. Firstly, slow sand filtering may not be that easy to set up properly and if it is not, may develop short circuiting and fail to remove the v fine suspension. Slow sand filtering also comes with maintenance requirements that again will lead to failures if not implemented properly. I recommend talking in detail to specialists such as Dryden Aqua or similar (I have no affiliation to any suppliers) before moving forward with anything on the ground. Secondly, you have not said anything about why the water is turbid in the first place. Is it possible to determine the cause (and if necessary change the abstraction / collection systems to decrease or eliminate the problem at soure)? A small investment in testing could also shed light on the composition of the turbidity and allow an assessment of its likely impacts on consumers. I appreciate milky water is not ideal, but if people can be reassured that it is clean and not toxic, that is better than clear water that is not! Hope this is helpful.
I agree with Dave that first step is to check if the water is safe to drink. If it is, it might well be easier to reassure people that the water is safe rather than find a technical solution to an aesthetic issue. If you do look at slow sand filtration further, you could make a small pilot unit in a large plastic barrel so see whether a) it works and b) equally importantly whether the users are willing and able to maintain the pilot unit before considering a full-scale filter. Maintenance is always the bigger problem, and slow sand filters need careful maintenance. Good luck
Typically this would be a case for using flocculants, but of course that requires an operated water treatment system with regular restock of chemicals, i.e. probably not feasible?
What is the source of these fine particles? Maybe some improvements of the intake could reduce them being washed out of the soil?
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I agree with Dave that first step is to check if the water is safe to drink. If it is, it might well be easier to reassure people that the water is safe rather than find a technical solution to an aesthetic issue. If you do look at slow sand filtration further, you could make a small pilot unit in a large plastic barrel so see whether it works and equally importantly whether the users are willing and able to maintain the pilot unit before considering a full-scale filter. Maintenance is always the bigger problem, and slow sand filters need careful maintenance. Good luck