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By Louis Torres on 9/13/2009 at 10:01:44 AM
We have a customer with colloidal clay in suspension in their water supply. The water has 0.7 parts of sulfur, 320 TDS as measured by a Hach field kit. The customer has a dual guard aeration sulfur removal system with power vent. The customer also has a backwashable filter media tank and a large 1-micron canister filter….
We have read that coagulation is the way to go to remove very fine colloids from the water source. We have also been told that the amount of retention for settling the colloidal clay is 10 times the pumping rate. Along with aluminum sulfate as the coagulant, we are looking for answers to the following questions:
1. Are there any other methods to remove colloidal clay from water other than coagulation?
2. How is the feed/dosing rate of the coagulant determined?
3. Are there any other coagulants that are used for removing suspended colloidal clays?
4. Will there be a need to remove any excess coagulant from the water after retention, and what is the proper equipment for that?
5. What is the best way to flush the suspended particles from the retention tanks?
6. Are there any other water concerns that can affect treatment or hinder treatment of colloidal clay, such as iron, pH, manganese, chlorides, etc.?
7. We believe there are iron bacteria in the water. Will that have any effect on the use of coagulants?
8. Could someone please tell us if sulfur should be removed before or after coagulation?
Dave Hedger: 9/13/2009 3:26:22 PM
You have a challenging problem. You will undoubtedly have to perform some bench scale tests to determine the best approach. There are a lot of coagulants to choose from, including nonionic, cationic and anionic. Of course, alum is the old “tried and true” coagulant used by many municipal systems.
If you''ve never done this before, you''ll need to set up a bunch of jars, and determine which coagulants work best for your particular water. Yes, pH, temperature, iron, iron bacteria, manganese, algae and many other contaminants will affect the outcome. I''d suggest getting samples of the coagulants mentioned above, and doing a rough screen test, injecting, say, 5 ppm (parts per million), 20 ppm, and 60 ppm of each into a jar of the water, mixing, and letting stand. A good floc will form within a minute or so when you''ve found the right coagulant.
Then, home in on the optimal concentration with further tests. Then you''ll also need further experimentation to find the right filtration media. The coagulant manufacturer can be helpful in making suggestions. If you want to explore bypassing the tedium of finding optimal coagulant conditions, you could explore the use of direct filtration using hollow fiber technology. I''ve had some success with these, although they are pricey.
Alan Hanna: 9/15/2009 1:00:18 AM
We have done several membrane systems on colloidal clay and glacial silt with great success. The systems may be pricey, but they work and the application is simple. We have also done collidal iron <0.5 micron — again, crystal-clear water. The unit we use is the GE Homespring, with membrane ultrafiltration. It is also certified to remove bacteria and viruses. [It has a] small footprint, easy application and crystal-clear water. P.S.: The membrane ultrafiltration will not remove heme iron color.
Jim Wark: 9/15/2009 4:05:46 PM
There are quite a few specialty chemical companies that make formulated products for this type of water. All basically are flocculants or coagulants, and with a good water analysis can cut down search time…. Other points to ponder:
1. Is it elemental sulfur or is it hydrogen sulfide (H2S)?
2. Iron bacteria usually leave a slimy, gelatinous film on the water tank in the toilet. Is it there?
3. Iron and manganese can affect treatment options. What levels, if any, are there?
4. Automatic timed solenoids can flush sediment as needed.
5. Sometimes aerating can reduce H2S odor in water without much extra cost.
6. Are there any tannins or heavy organics in the water?
Leon Stepanian: 9/24/2009 1:05:59 PM
The first thing we do with clients with a deep well and fine clay is to get them to have the well inspected…for surface water infiltrations…. Just get the well sealed a good 10 to 20 feet below that infiltration level. This has saved many of our clients major system requirements plus the hassle of dealing with the problem. There is always a chance that the well water production rate will drop, so this has to be taken into consideration.
One client had the same problem, but we used three 20" Big Blue filters in parallel with 1-micron spun polypropylene depth filters in each. The parallel of three housings slows the water flow enough so the filters can filter out the clay.