Manganese removal options

[omnia]

Hello , I've heard about a system to removal manganese based on sand/pyrolusite bed filtration.
Does anyone tell me more about this ?

 

[DocMax]

Hello Omnia;
To reduce the manganese in the water I suggest two process; the first one is an oxidizing process by the action of sodium hyochloride and air followed by a filtration in a pressure sand-anthracyte filter.
The second is by the greensand (pyrolusite) filters.
Manganese greensand is a purple-black filter medium coated with manganese oxide.
This coating provides the greensand with special oxidation properties for removing iron, manganese and small quantities of hydrogen sulfide.
There are two process:Intermittent regeneration (IR); and
Continuous regeneration (CR).
In the IR process the water flow on a bed of greensand (a minimum bed depth of 610 to 762 mm) in a pressure filter.
When the filter is clogged a backwashing is necessary to remove the solids particles in the filter, after this it's necessary to regenearte the greensand by potassium permanganate. This chemical is best used when the water pH is above 6.2 and below 8.0.
Raw water with a naturally lower pH should be adjusted to a minimum pH of 6.2 before treatment with manganese greensand.
The IR process is limited to water with a maximum combined iron-manganese concentration of 10 to 15 mg/l and a maximum sulfide concentration of 2 to 5 mg/l.
If the water contains appreciable amounts of iron, chlorine injection or aeration should be included as a preoxidation step in the treatment process.

CR method
The CR method involves the oxidation of iron and manganese to solid particles, followed by filtration using manganese greensand or a manganese greensand and anthracite bed.
The CR method is generally used when iron predominates in concentrations up to 15 mg/l or more and only small amounts of manganese are present.
The CR process involves feeding a predetermined amount of oxidant (sodium hypochloride) or combination of oxidants, such as potassium permanganate and sodium hypochloride, to the raw water before contact with the manganese greensand bed.
This prechlorination step will oxidize the bulk of iron, as well as any sulfides, which will be filtered by the manganese greensand bed and must be removed at regular intervals through backwashing.
The potassium permanganate will complete the oxidation of trace amounts of iron and soluble manganese, but the medium must remain in a continually regenerated form at all times.
This is accomplished by a visual check for the faint pink tinge in the filter influent or the presence of chlorine in the effluent

This is all

 

[sbush]

Pyrolusite is naturally mined, nearly pure, manganese dioxide ore. It can be crushed and graded to a wide range of sizes. It is used in many industrial products such as dry cell batteries. Pyrolusite is used more commonly for water treatment outside of the USA where Greensand is predominant. In the 80's, Ken Zabel & Associates teamed up with American Minerals to manufacture and market the product in the U.S. under the trade name "Pyrolox". Zabel and American Minerals parted company, a few years ago. He is now affilliated with Pentair and they now market a product called "Pentapure".

Pyrolusite is an excellent media for oxidizing and filtering iron and manganese from water. However, it doesn't work any better than other less expensive and commonly available materials, such as manganese-dioxide coated sand/anthracite. As with most manganese-dioxide based processes designed for iron and manganese reduction, pyrolusite requires a bed of a sufficient depth for contact time and filtration (24 - 30 inches is typical), flow direction is typically downward in filter mode, a source of oxygen is continuosly added ahead of the filter for catalytic oxidation of iron and manganese on the media, however, sufficient oxygen may be present in some water supplies to preclude artificial addition. The source of oxygen can come from an aeration device, chlorine, potassium permanganate, ozone, and many more. Backflushing with clean water in the upflow direction at a velocity of 15 - 20 gallons per minute per square foot (plan area) is usually sufficient to restore flux and or headloss to normally levels. As with all iron and manganese removal filters, periodic air scouring is desireable. Filtration rates range from 2 gpm/sf to 5 gpm/sf. With pilot testing, higher rates may prove to be attainable.

Several filter manufacturers such as Filtronics and Layne Christianson have begun marketing pyrolusite as a proprietary media and process. (There really isn't much that is new in water treatment but it doesn't stop clever salesmen from trying).

You can buy this material from Pentair, Clack Corp., and other water treatment component and media distributors. If you can handle container sized quantities, then it is easy to source suppliers overseas (China, India, Africa, South America) for better rates than U.S. suppliers even with the addition shipping costs. For drink water applications, NSF-61 listings may not be available from all suppliers so you should check carefully before you buy.

Less than truck load quantities of pyrolusite from U.S. suppliers will typically sell for $40 - $60 per cubic foot (and higher depending on the number of middlemen).

S. Bush

http://www.water-eg.com

 

[omnia]

Maxfab ,sbush thank you for reply .
sand/anthracyte pressure filter with pre-oxidation step in my experience is not very effective:

manganese in : about 2,5 ppm
manganese out : 0,9/1 ppm
Oxidation with ozone.
The problem with ozone is overdosage. It oxidizes Mn (II) to Mn(VII)in a form that leaks out the filter.
I have to revamp a plant treating 30 m3/h ; I've heard the good performances of a mixed bed sand/pyrolusite (20x50 mesh). it seems that the investment and running costs are much lower than traditional greensand (no doubts , it works!).
Do anyone have experiences about it?

 

[sbush]

Mixing pyrolusite with silica is commonly done. In a test of well water containing 1.0 mg/L iron and 0.35 mg/L of manganese with aeration to 60% dissolved oxygen and pH of 7.5 and a pilot filter column having an empty bed contact time of 12 minutes, the results were as follows:

at 10% mixture, iron = 0.01, manganese = 0.05

at 20% mixture, iron = 0.01, manganese = 0.02.

Yes, this process is as effective and reliable as manganese greensand.

Greensand is a substrate material. By itself, it will not reduce soluble iron or manganese levels. What makes Greensand work is the manganese dioxide coating that is artificially applied to it. It is the manganese dioxide coating that is reacting with iron and manganese. Almost any surface can be coated with manganese dioxide, such as sand or anthracite. When manganese Greensand was developed by Hungerford & Terry, they very wisely picked a unique material to coat that was not commonly available and that they pretty much had exculsive rights to by ownership of the mine. They could have coated common sand or anthracite, but so could anyone else, hence Greensand evolved and became the standard for a long time because no one else figured the "secret" until recent times.

Any thing that contains manganese dioxide will act as a catalyst to oxidize iron and manganese. If manganese is present in the natural water supply, it will eventually coat common filter sand with manganese dioxide and the sand will perform like a Greensand filter too. If you can't wait for this coating to develop naturally, you can mix pyrolusite with the sand and it will accelerate the natural process. You can also bathe the sand in a solution of potassium permanganate and accomplish the same end.

Now having said all this, please be aware that just like manganese Greensand, these alternative medias might not work in all cases. There are certain situations where conventional oxidation/catalytic media (Greensand, pyrolusite, MnO2 coated sands) filtration won't work without special techniques applied. Therefore, it is always a good idea to pilot test an application before proceeding to a full blown design. Also, work with a professional who has a lot of experience with the process. There are a lot of people who try and fail because they don't have firsthand experience.

S. Bush

http://www.water-eg.com

 

[zinman]

I have direct experience with about 20 municipal iron and manganese systems that utilize either silica sand, or manganese greensand, plus antracite. All have worked well, for up to 25 years so far. One of the older plants using greensand was recently replaced with a pyrolusite system, which the owner says doesnt work as well as the old system. The main objection is that it backwashes more frequently than the old system. If practical, a pilot test using pyrolusite should be completed before adopting it.

 

[semo]

Let me begin by saying I agree with everything SBush has said already.

I have several plants with pyrolusite/sand mix. Ranging from 10% to 30% pyrolusite. Pilot tests were performed on several of these to find the mix. The media is too expensive to do a 100% mix; plus, it won't give any better performance than an appropriate lower mix does. These have all been gravity filters and not pressure filters; therefore, I do not have experience with the pressure filter application. We typically do them with greensand as most manufacturers include the media.

A lot of information has already been given on the pyrolusite and greensand as mentioned above by SBush and DocMax.

As with greensand, the pyrolusite requires an oxidant such as permanganate or chlorine ahead of the filter. On greensand, the coating performance will deteriorate without the oxidant, thus the reason mentioned above for the two manners of regeneration.

One thing that I have found as SBush said is many of the regular sand/anthracite filters that we have in service have generated a manganese dioxide coating on them over time and act as greensand. Therefore, I feel the pyrolusite just gives the filter some early conditioning.

A good source we have found for pyrolusite information including pilot testing and filter audits is Tad Bassett with AWI-Anthratech in Utah.

Hungerford & Terry (Inversand) now has a relatively new media "Greensand Plus" that has the coating on a silica substrate (instead of glauconite like Greensand), thus allowing different media sizes.

When the iron/manganese levels begin reaching higher levels, oxidation followed by clarification (with solids contact units and polymer addition) can be used to extend the filter run times. Pilot studies can and should be used prior to your final design.

Your full water analysis should be taken into account. As mentioned above, other metals and organics can rob the manganese oxidation process when chlorine or permanganate is used if their dosage is not correct. Note that the oxidation time with manganese and chlorine is higher than that of iron so some reaction time is necessary prior to filtration.

Beware of some of the proprietary (little black box) systems. Do some investigation on older installations as I have seen some that pilot test and work fine for a while when their media is still "hot"; but, then the media activation deteriorates and the system no longer works.

 

[bimr]

Let me begin by saying I agree with everything SBush and semo have posted.

I do not believe that it was previously addressed, but you need to be aware that the filter media’s specific gravity may vary depending on which media is selected. The filter backwash rate is set by the specific gravity of the filter media that is used. For the same reason, you also have to be careful when you mix different media.

Secondly, you need to be aware of the application (which you have not addressed). Some of these filter medias are more suited to residential products. Other manganese removal processes are more cost effective for large industrial or municipal applications and where you are trying to remove higher concentrations of iron or manganese.