The river is actually effluent water after primary treatment and I catch them downstream. Water has much TSS, naturally, with COD of ca. 60 ppm. We are looking for a large volume, but not very large of about 10K cubic meter a day. We are thinking to throw back those TSS's we catch to the river and use the water for irrigation. Using a filter is not efficient since those are pricey and get clogged fast. We thought about a settling tank with an opening from below. Any better idea? A kind of DIY thing would be best.
Settling tank is an excellent idea. You can also add salt to the tank to speed up the settling. Centrifuging is good but can be costly to instal pumps.
Dear Ami, perhaps a river bank filter (rbf) may help you to avoind the presence of TSS in the inlet water so you may have less changes in the water quality (at least related with suspended solids) during raining and dry seasons. There are some reports where authors claims that rbf are capable also to remove some organics, microorganisms and some other pollutants. Indeed, you may use other conventional water treatment processes after rbf.
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Continuous sandfiltration could be a feasible technology for your application. Such filters can handle large volumes at very low operation costs and low clogging tendency.
Look for "Confiflow sandfilter" at www.huber.de, "Astrasand" at en.paques.nl/pageid=58/ASTRASAND%C2%AE.html
or any other manufacturer.
(Key terms: continuous sand filtration, moving bed filter)
The cost efficiency of a settling tank depends on the settling velocity of your particles. As first guess your surface load (q=Q/Surface area) should be lower than the settling velocity. In worst case a large ratio of TSS is not settleable at all. So without knowing more details it is difficult to give advice. There are different settling characterisation methods available which may help to evaluate feasibility and nesseary design of a settling tank.
additives such as ferric chloride and aluminum sulfate at low ppm levels say 2-10 ppm can be effective in removing hydrophilic suspended solids and their combination with anionic polymers like hydrolyzed polyacrylamide can improve this but I don't know the details.
Riverbank filtration could indeed be an effective and low-cost option. You'll probably have to re-aerate your water again after substraction, but cascade aeration is a low-cost solution for that. In the Netherlands, the traditional treatment for TSS is coagulation/flocculation and sedimentation. If land availability is limited, you can use lammela separation.
Dear Dr Bachar,
Much the cheapest and generally most reliable alternative is usually plain settling but would probably be problematic with the source you describe even with sufficient area.
Several of the responses note the need for additional information, but they and others provide excellent suggestions. The bank filter can be very effective and an hybrid, designing a bank filter as a dynamic roughing filter, might be much the cheapest and very much an alternative that can be undertaken by a community or small industry at minimum cost. You might want to begin with the maximum size/density of TSS that you can utilize then design for that; after the filtration step storage would probably be based on quantity needs as relatively little effective settling without flocculants could be expected, normally.
WOW!!! Thank you all very much. good ideas flow among good people and really make the world a better place. It is really nice to see so many good advice for free on the web. Please dont stop. share knowledge as you do. Thank you all very much. I will look up more info on the web with your leads and answers.
Ami
Agree with Enrique La Motta - hydrocyclones (HC) may be the most effective solution if you have enough pumping power. Properly designed, HC can remove both denser and lighter particles (denser go to the perimeter, while lighter tend to group in the center axis. If dissolved solids are problem, too, add coagulants just before the HC. Roughing filters are also excellent solution - just provide for proper washing. The very best is RBF which is used also for drinkihg water abstracton close to (polluted) rivers. Enjoy science!
I agree with river bank filtration, since you are already planning to refuse the TSS back into the river you can keep them their. This is probably the cheapest choice if you have a river band with plenty of sand. Otherwise you can use slow sand filtration, in your case you will need around 10000 square meters of area for this, and would have to clean the filter around 1 time per month. Solutions with chemicals addition can compromise your plan of refusing TSS to the river, but will increase the settling tank efficiency. You can also check on settler with laminas, that are very common on water plants.
quick thoughts
1. Either generate Particle Size Distribution (PSD) data or, conduct jar testing and subsequently settling rate testing.
2. Start w ferric chloride, PAC (Aluminum), AM/DADMAC, DADMAC w Ferric. if none of those work try a high charge density anionic. Once best chemical program is selected - run settling rats testing.
3. Settling rate testing will yield some guidance w respect to efficacy if settling tanks, weir tanks, clarifiers.
4. Do consider the ability to remove settled solids - conical bottom tanks, Llamela style clarifiers.
5. CAPEX can outplay OPEX - so picking the best tool is ultimately important.
6. PSD data will reveal solids settle-ability of the solids and what micron size filtration would be required to achieve the desired TSS or turbidity values.
7. As mentioned above, seasonality is a very important variable.
Dear Ami Bachar
Hydro-cyclone is the best possible way to out the suspended solids from this huge water at an economical rate.
https://www.youtube.com/watch?v=lRBPQmectLQ
However it is important that you characterize the suspended solids. both approaches using floating living islands and by promoting algal blooms which function like flocculation agents ,(replacing costly flocculants like those mentioned in an above reply). What is the origin of the TSS in the river ?
However it is important that you characterize the suspended solids first, eg. the surface charges and the composition ( organic or clay like and the prevailing size ) and further define what to do with them and how they can be disposed off. why would you put them back in the river ? Does not make sense ?
1. Jar test.
2. the ten ppm anionic and cationic
3. Most solida are anionic but there are sone which are naturally cationic. If anionic ”does something to the solids then do following w opposite charge.
4. add a homopolymer of DADMAC, w MW 50,000 to 100,000. in your set of jars, do a 10, 20, and 30 ppm active polymer. You will see floc form and settle. If floc forms but does not settle, add an anionic, HMW polymer, Maybe 5 to 10 ppm.
the polymer will settle the solids in a container - a frac tank or a weir tank. Have a bottom draw to take put solids.
thag is a very cheap and effective way of removing TSS.
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