Fe & Mn Utilizing Greensand & KMNO4
Fe & Mn Utilizing Greensand & KMNO4
(OP)
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!





RE: Fe & Mn Utilizing Greensand & KMNO4
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.
RE: Fe & Mn Utilizing Greensand & KMNO4
RE: Fe & Mn Utilizing Greensand & KMNO4
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
www.water-eg.com
RE: Fe & Mn Utilizing Greensand & KMNO4
RE: Fe & Mn Utilizing Greensand & KMNO4
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
www.water-eg.com
RE: Fe & Mn Utilizing Greensand & KMNO4
S. Bush
www.water-eg.com
RE: Fe & Mn Utilizing Greensand & KMNO4
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
www.water-eg.com
RE: Fe & Mn Utilizing Greensand & KMNO4
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/
RE: Fe & Mn Utilizing Greensand & KMNO4
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.