Dear Researchers,
I have to speed up the sedimentation time of a suspension including microparticles. I am looking for a non-toxic additive that can increase the precipitation time. It could be any materials for instance charge-neutralising agent. I really appreciate your help regarding the discussed issue.
Best regards
Ali Dadfar
Hello Ali Dadfar,
Sedimentation is sometimes combined with coagulation-flocculation process in the water/wastewater treatment system (WTP/WWTP) to increase its sedimentation rate. Conventionally, coagulants are used through chemical precipitation, by adding them to the body of water. Usually, coagulants used are Alum (Al2(SO4)3), Ferric chloride (FeCl3), Ferric sulfate (Fe2(SO4)3), and cationic polyelectrolytes.
It will coagulate colloidal matters in your water (even soluble particles that have hydrophilic property), thus your objective to fasten the sedimentation process up to microscopic level should also be possible to be achieved. Plus, it is a term in water technology to use non-toxic, cheap, and easy to dispose type of coagulants. Therefore, you don't need to worry anything about its hazard. Also, (some) coagulants are also cationic/anionic in the first place, so it could provide neutralization of ion-charge of your water.
I suggest that you look over for each of those coagulants to understand its properties and hoping that you can decide which is the best for your condition.
If you get any more question, I will be open for discussion.
Best regards,
Rumi Azhari
Muhammad Rumi Azhari Nur Irfani thank you so much for your helpful and fruitful reply. I am afraid if I work with the chemicals that you already mentioned as they might come to the final product. Do you have any other suggestions (i.e. another chemical that increases coagulation) which can stay in the final product without any issues?
S.M.Ali Dadfar Your welcome.
As much as I know, the coagulated particles together with their coagulants will precipitate down to the bottom, leaving upper part of water (we call it "super-natant") to be very much clearer. If you are treating normal water with its standard pressure, buoyancy force, etc., the chemical that you add will be going down also. So, there's nothing to be worried about. It's very similar to the actual sedimentation anyway, since in sedimentation you're just extracting the super-natant part of the water.
But remember that coagulants are cationic/anionic. It means that they will push all over each other, creating distance between ion-charged coagulants (imagine it like magnet positive-positive). So, if you add too much of its concentration, it's possible that your super-natant volume will be smaller because the coagulants will be further spread out upwards. To avoid that, you must find the exact concentration that you need. To do so, you have to do a jar test (you can look up how to do it).
Anyway, as I said earlier, most coagulants are not toxic. So, even if it's consumed, it will be ok (as long it's in small number). Although, I doubt it will be consumed if deployed properly.
Muhammad Rumi Azhari Nur Irfani thanks again, however, I am interested in the sedimented particles not in the supernatant and would like to be sure that there is no residue in the sedimentation and that the added chemicals stay in the supernatant.
S.M.Ali Dadfar Hmm, if that's the case, I think you have to try other alternatives aside from chemical addition. Because as much as I've known from my environmental engineering career, common types of chemical addition will inevitably bond with the particles. So, your solution would not be fastening up sedimentation rate. But instead, it's about how to extract solids from its water suspension state.
The only thing that I can think of as a solution is through filtration; where you will gather the particles you want from the filtrate layer. Reverse osmosis (RO) will do very well for that, and since RO is quite a common tech you can find, it will be an easy job to do. Keep in mind about your particles size, whether you will be using microfilter, ultrafilter, or nano filter.
Another alternative is by using the old-classic distillation process. It will do very well for your case also, assuming that your targeted particles were not sensitive to temperature.
I can answer more if you provide more detail about your project, since I cannot measure comprehensively precise methods if I don't understand the materials and objectives.
Regards,
Rumi.
Muhammad Rumi Azhari Nur Irfani, Thank you so much for your helpful and fruitful information. I found your comment very interesting and will contact you if I need more assistance.
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