Manganese
Manganese will cause a black stain and will many times be accompanied by iron and hydrogen sulfide gas
odor. In combination with iron, manganese staining will sometimes be chocolate colored or brown. Evidence
of manganese staining is usually most prominent in the dishwasher. The detergents used to wash the dishes
raise the pH of the water high enough (>8) to allow the manganese to easily precipitate. A second place to
see a manganese problem is on the top of the water in the toilet storage tank. The manganese will form a
film that is sometimes mistaken for oil on the water. If you touch the surface of this water, the film will break
into flakes with jagged edges. At high concentrations (>.2 ppm), the manganese will give the water what is
sometimes described as a sweet taste.
Manganese generally exists in two forms
Manganous manganese - This form of manganese is invisible in the water just like dissolved sugar is. Just
like sugar water, the manganese can not be mechanically filtered from the water. This is the most common
form found in our local water.
Manganic manganese - This form has precipitated (formed a solid and is no longer in solution - it has turned
to rust - "oxidized") and gives the water a cloudy black appearance. This form of manganese can be
mechanically filtered. It is rare to find manganese in our local water in this form. The reason for this is the
waters in our area rarely have a pH above the 8 required to oxidize the manganous form into the manganic
form.
Although manganese is generally not considered to be a health risk, a level of greater than .2ppm is a cause
for concern. The State of Maine does recommends that greater than .2 ppm be reduced because of potential
health risk considerations.
Treatment
Manganous manganese can be treated two ways. The most common way to treat manganese is to use
a water conditioner or softener to remove the manganese by ion exchange (see the section on hardness
to better understand this process). This method can be used on almost any level of manganese. This
method will only be successful by itself if all the manganese is in the manganous form, the TDS is relatively
low (generally <500ppm), the pH is low ( generally <8) and very little oxygen in the water. The TDS has to
be low to assure that there is no bleed through due to the manganese being removed from the resin once
attached. High TDS indicates there are other minerals in the water competing for the sites on the resin
(media) the manganese has attached to. The low pH and low oxygen assure that the manganese will not
oxidize while attached to the media (resin). If the manganese oxidizes once attached to the media, it can not
be removed during regeneration.
A second method to remove manganese, is a two step process called oxidation filtration. The manganese is
first oxidized by the use of either oxygen, chlorine or potassium permanganate. The oxidation causes the
manganous manganese to form manganic manganese. The manganic manganese is then removed by
filtration. This method is not typically used on very high concentrations (> 8 or 10ppm) of manganese
because the filter beds will require more frequent backwashing (automatic cleaning) then is reasonably
possible. This method will usually require the use of some kind of pH correction because manganese will not
oxidize below a pH of 8. Some water treatment companies will try to convince their customers that the pH
does not have to be above 8 to remove manganese. THIS IS NOT TRUE AND DON'T LET THEM GET
AWAY WITH IT. There are several types of oxidation filtration systems used today. They areAir Injection (our preferred method) - Oxygen in the air is used to oxidize the manganese, the system
requires the use of a venturi to inject the air. The system is therefore called an air injection system. There
are many brand names for this type of system but they all require a minimum flow (usually at least 5 gpm)
from the well pump to make the venturi work. This flow must be tested (see pump flow test instructions)
before this type of system can be used. Good systems will consist of 3 parts- venturi, air release tank, and
filter tank. The air release tank removes any undissolved air and allows for the retention of the water. If the
air is not released, severe spitting will result at the faucet. The retention allows time for the oxidation reaction
to take place. The filter tank removes the precipitated (manganic) manganese that was formed by the
oxidation process.
Chlorination systems (our second choice) - Chlorine is introduced into the water by one of two methods. The
chlorine can be pumped in with a solution feed pump or it can be dropped in tablet form directly into the well.
The water is then either sent to a retention tank and then to a filter or it can be sent directly to a filter. The
choice of methods will be determined by the severity of the manganese problem and the type of media
chosen for the filter tank. If chorine is used, it may be desirable to remove it with carbon. If the manganese
levels are low (<2ppm), the carbon can also be used as the filter that removes the manganic manganese
that is formed. If the manganese is greater than this (2ppm) than a separate filter with filter AG should be
used to remove the manganic manganese so the carbon will not be fouled. Some people will opt to use filter
AG as the filter and only use carbon at a sink as a P.O.U (point of use) treatment to remove the chlorine
from the drinking water. If this is done, there will still be chlorine in the water at all other faucets and
showers. The chlorine should be able to be regulated so that it is of no higher a concentration than that
found in city water. CARBON IS NOT TO BE USED UNTIL THE WATER IS CHECKED FOR RADON
BECAUSE THE CARBON CAN BECOME A RADIOACTIVE SOURCE.
Greensand systems (NOT USED BY US)- This method uses a catalytic media (called greensand) coated
with manganese that is treated periodically (like the regeneration of a softener) with potassium
permanganate. The potassium permanganate acts as an oxidant (like the chlorine or air). When the
manganese in the water comes in contact with the surface of media it oxidizes and the manganic
manganese is then filtered out by sticking to the media before it finds it way through the filter. We do not use
this method because these systems can easily bleed manganese into the water and the potassium
permanganate is not only poisonous, but, if spilled, stains badly. The manganese that bleeds into the water
can get to levels high enough to be toxic. You will hear these filters referred to as manganese filters,
greensand filters or potassium permanganate filters.
Catalytic Media (NOT USED BY US) This method or treatment uses a media similar to greensand. The
media has many different trade names but is usually a naturally occurring mineral called pyrolucite
(manganese dioxide). This method of treatment counts on there being enough air in the water to provide the
oxygen necessary to turn the manganous manganese into manganic manganese. This media can also
bleed manganese into the water. It doesn't work to remove manganese in the water we find locally because
there is not enough naturally dissolved oxygen. A second major draw back is that the media is so heavy it is
very difficult to back wash properly with the flows available from most residential pumps.
Manganic manganese can be removed by any of the backwashing filter commonly used. Since the
manganese is already oxidized the water only needs to be filtered. Generally the manganese will be filtered
with filter AG or Calcite.