Fe & Mn Utilizing Greensand & KMNO4 4

[globalwateresources]

We are looking into treatment of 270 gpm groundwater well with Fe (10 ppm) and Manganese (5 ppm). I am considering a pressurized manganese greensand filtration system with NaOCl (preoxidation of iron). KMNO4 is added at backwash for re conditioning of the media, and an orthophospate is added to the finished water stream for sequesteration of any Fe&Mn that makes it past the pressure filter. I am using an open-air modified dumpster with a cloth media fabric that will drain the backwash water while trapping the solids from the backwash stream. Can anyone give insight to the expecteded range of media, KMNO4 and Ortho requirement? Any improvement suggestions would be greatly appreciated!

 

[bimr]

The manganese greensand process that you have proposed is only economical for iron concentrations less than 1-2 mg/l.

Polyphospates not orthophospates are used for sequestering iron. In any case, you will not have to sequester iron since the iron removal system will remove all of the iron.

The cloth media filtration process is probably not going to work either.

You need to investigate the air oxidation process using pressure filters.

 

[globalwateresources]

Thank you for your post - are there methods of inducing aeration into the pressurized stream without the use of an intermediate tank befor filtration?

 

[sbush]

At 10 ppm iron and 5 ppm manganese, your water supply is at the point where you really need to consider oxidation and pre-settling of iron and manganese ahead of filtration. Otherwise, the loading is too great for reasonable filter runs to be expected. This is true for manganese Greensand, silica sand, Birm, pyrolusite or any other type of granular filter media.

There are ways of introducing aeration in a pressurized system for iron/manganese reduction; however, in this case pre-sedimentation (i.e., a settling tank) is necessary for sufficient run times.

Typically, a 1 ppm dose of polyphosphate is added to the finished water.

The cloth filter has been used successfully in some applications where backwash water is collected in a holding tank then decanted. In these applications, a cationic or anionic polymer is used to thicken the "sludge" prior to the cloth filter device. Field testing is recommended to determine which coagulant works best.

There is a company that manufactures a large "bag filter" for use with a typical roll-off cart and they are targeting the sludge dewatering market with this product. If you are interested, I can send you a name and number for contact.

S. Bush

http://www.water-eg.com

 

[globalwateresources]

Thank you for your post. It was most helpful. If you have time, I am interested in any information you can provide for the Bag Filter. BTW - are you familiar with Pureflow removal systems (

http://www.pfdiv.com)?

They have a system that is treating water in Yuma Arizona, which is some 12 miles down river form this site. They are claiming adequate removal w/o the use of KMNO4, just chlorine. I am assuming this is a sand/anthrocite type application, but they have to be treating relatively similar concentrations (previously posted). We are using the sand/anthrocite cap with chlorine and are having less than successful results. From your post, I gather that the sand/anthrocite application may not be sufficient with these concnetrations, and may need to drop back to the KMNO4/Greensand approach.

 

[sbush]

I overlooked your request for alternative suggestions, in my previous post.

This application would be excellent for lime-soda softening if softening was also necessary in addition to iron/manganese reduction.

Assuming that softening isn't necessary, then I recommend that you pre-oxidize the water with chlorine. Feed enough chlorine to carry a residual after the treatment process. Immediately after chlorine injection and prior to setting, add a coagulant such as filter alum to speed up the settling process. The alum dosage will probably never exceed 20 mg/L and typically will average 10 mg/L.

Pass the chemically dosed water through a settling chamber with tube settlers to accelerate the settling process. Use a loading rate of 2 gpm/sf. Lamella plates would work as well, but tubes are easier to service. Provide a hopper bottom to collect and periodically blowdown solids.

At this point, you can either gravity flow through a filter or re-pressurize using a pump and flow through a pressure filter.

The filter should be designed for a 3 gpm/sf maximum loading rate and a 15 gpm/sf minimum backwash rate for 10 minutes duration minimum. Air scour feature would be benificial for long-term operation. Simultaneous air/water wash would be desirable for reduction of backwash water volume.

The filter media can be 18" of silica sand and 12" - 18" of anthracite. The media should be coated in the field with manganese dioxide at the time of start-up. No further recoating will be necessary as long as chlorine pre-feed is maintained.

In larger volume systems, it might be desirable to consider aeration as opposed to chlorine as the primary oxidation method in order to cut down on operating cost of chemical. However, at 270 gpm the cost savings might not be that great given the added maintenance required by the heavy loading of iron and manganese and their effects on the aerator device (i.e., metal oxide build-up on slats and trays). Even using a high-efficiency aerator, you will still need to feed supplimental chlorine.

If this application is for potable water, then you should also check with your local regulatory agency in charge of water plant design for further instructions and advice.

S. Bush

http://www.water-eg.com

 

[sbush]

I'm somewhat familiar with Pureflow. They are former Filtronics people. Filtronics uses their own "proprietary" media which they call Electromedia. This media is either all pyrolusite or a mixture of pyrolusite and sand. I would assume that Pureflow is following the Filtronics model since everything else associated with their filters looks identical to Filtronics. In any case, as I said earlier, any granular media (including manganese Greensand with KMnO4) is going to need pre-settling for reasonable run times. If the Pureflow's system at Yuma is working on the same water quality as yours with 10 ppm Fe and 5 ppm Mn, then they are backwashing those filters hourly. The direct filtration process will work for a period of time; however, the filter runs will be extremely short.

S. Bush

http://www.water-eg.com

 

[sbush]

Global,

Send me an email using the link below. When I get back to my office, I will send the info on the "bag filter" manufacturer. I don't have it right now.

S. Bush

http://www.water-eg.com

 

[bimr]

Regarding: "They have a system that is treating water in Yuma Arizona, which is some 12 miles down river form this site. They are claiming adequate removal w/o the use of KMNO4, just chlorine."


The use of KMNO4 and/or chlorine will be expensive with the amount of iron that you have. That is why most people use air oxidation followed with chlorine to remove the last traces of iron.


Regarding the dewatering of the residuals, bags are something that have been used for dewatering of dredgings, not so much water treatment solids. You may want to consider the dewatering screens:

http://www.gravityflow.com/

 

[semo]

Using Chlorine only as your oxidant, you will be looking at over 14 gpd of hypochlorite for 270 gpm. The aerator will reduce this; but, something that hasn't been mentioned yet, is the pH of the water. At a 2:1 Fe/Mn ratio, you need to worry with the Mn. The iron will come out easily. The Mn however, with only Cl or O2 will have to have a pH above 8 to 8.5 to readily oxidize the Mn. This could require the addition of another chemical. The KMNO will take care of the Mn at lower pH's; but, if you use a coagulant in the sedimentation, it might also require a slightly higher pH.

I agree that you will need sedimentation or you will overload your filters with the iron/manganese mass and get short filter runs.

Adequate treatment will not require the use of polyphosphates following filtration. I know some municipalities that use them; however, most do not.

Be careful of what the manufacturer claims in Yuma. I have had experience with Filtronics. Contact some of their installations and find out from the owners how the process is working. And look at installations that are a few years old. Lots of claims are made when the media is still hot; but, performance sometimes deteriorates later.