Filter Media

Filter Media

What it is and how it works

Birm is a black granular filter material used for removal of iron and/or manganese from water in pressure or gravity systems. It contains an active insoluble catalyst to precipitate iron and/or manganese. Because the presence of iron is most common, iron removal is the usual application for Birm. Under suitable conditions, the iron and dissolved oxygen in water react on contact with the Birm filter bed and, as a result, the iron is precipitated in the form of hydroxide. This is a flocculent material which is filtered out in the bed of Birm. Periodic backwashing flushes out the accumulated iron and the Birm is again ready to perform its function. Birm is not consumed in the iron removal operation.

Advantages

• No chemicals to purchase for maintenance. Regeneration not required.
  
• Iron removal efficiency is extremely high.
  
• Negligible labour cost. Only periodic backwashing required.
  
• Durable material with a long life.
  
• Wide temperature range application.

Conditions necessary for the use of Birm

Iron Removal

• No hydrogen sulphide present.
  
• Organic matter not to exceed 4-5 ppm as indicated by the oxygen consumed value.
  
• Oil must not be present.
  
• A dissolved oxygen content of at least 15% of the iron. (Example Iron = 10ppm.
  Dissolved Oxygen = 1.5 ppm or more).
  
• A pH of 6.5 or higher.

Note: The correction of waters having a pH of less than 6.5 can be accomplished by several methods. Aeration, the use of Corosex "F" (CLACK neutralising method), or the addition of chemicals, such as soda are examples of common methods frequently used. A combination of the above methods is often used, depending on the amount of correction desired. The dissolved oxygen content of a water supply is raised by proper separation.

Manganese Removal

The removal of manganese from water by the catalytic action of Birm usually requires a higher pH than is required for iron removal. Such water should have a pH in the range of 8.0-9.0.

The dissolved oxygen content should be 15% or more of the total manganese and iron expressed in ppm.

Other conditions are the same as for iron removal.
For manganese removal, consult our laboratory.

General data

Birm is furnished in two grades: regular and fine. Regular Birm is generally recommended for industrial and municipal installations. Fine Birm is recommended for domestic application or in cases where the available backwash water is limited. Bed expansion of 35 to 50% in backwash is required for best results. 12 to 15 GPM per square foot are required for backwashing regular Birm. 8 to 10 CPM per square foot are required for fine Birm.

Instructions for industrial and municipal installations

• Bed depth: 30 ­ 38 inches.
  
• Standard graded gravel supporting bed depth ­14 inches or more.
  
• Service flow rate: not to exceed 4 GPM per square foot.
  
• Freeboard space: 35 to 50% of bed depth.
  
• Backwash whenever the pressure loss through the bed increases by 2 to 3 pounds per square inch. Backwashing is usually complete within 20 to 30 minutes.

Instructions for domestic installations

• Bed depth: approximately 24 to 30 inches.
  
• Standard graded gravel-supporting bed ­ 8 inches or more.
  
• Service flow rate: not to exceed 5 GPM per square foot.
  
• Freeboard space: 35 to 50% of bed depth.
  
• Backwashing is recommended every 10 days to 2 weeks. In treatment of high iron content waters, backwashing more frequently is desirable. If 8 gallons per minute per square foot of bed are not available for backwashing fine Birm, an air wash is recommended. This may be accomplished by drawing air through an injector into the water for backwashing.
  

Rain water, in its passage through the upper soil layers, picks up carbon dioxide and humic acid from decaying matter as well as certain minerals and other organic materials. As it continues through clay, limestone, shale, sand, or other beds, it dissolves various amounts of calcium, magnesium, iron manganese, sodium and silica, and loses most of the organic materials. The amount of chlorides and sulphates dissolved also depends on the strata contracted.

The dissolved iron is largely in the form of ferrous bicarbonate due to the excess of free carbon dioxide. Oxygen dissolved the rain or contracted with the water in the soil above the water table remains in the water. The iron as ferrous bicarbonate, in the presence of free carbon dioxide, has a lower activity and does not react with the oxygen to form a filterable hydroxide, but remains in solution as the bicarbonate, even at a pH above 7.0.

Birm is a black granular filter material used for the removal of iron and/or from
water in pressure or gravity systems. It contains an active insoluble catalyst to precipitate iron and/or manganese. Because the presence of iron is most common, iron removal is the usual application for Birm. Under suitable conditions, the iron and dissolved oxygen react on contact with Birm filter bed and, as a result, the iron is precipitated in the form of the hydroxide. This is a flocculent material, which is filtered out in the bed of Birm. Periodic backwashing flushed out the accumulated iron and the Birm is again ready to perform its function. Birm is not consumed in the iron removal operation.

To more fully understand the reactions involved in the precipitation of iron and manganese, the following table gives the theoretical pH value at which metal hydroxides begin to precipitate in the absence of hindering ions.

pH	Metals
11.0	Magnesium
10.0
9.0	Manganese, Silver, Mercury
8.0	Colbalt, Nickel, Cadium
7.0	Ferrous Iron
6.0	Zinc, Copper
6.5	Chromium
5.0	Aluminium
5.1
4.0
3.0

Hindering ions

Organic materials are usually coloured and act as sequesting ions for both ferric and ferrous iron in holding it in a chemically-bound soluble complex. For example, the iron in haemoglobin of the blood is solubalized in a similar manner.

Free carbon dioxide reduces the activity of dissolved iron to react or precipitation
from solution.

Certain combinations of dissolved minerals tend to form only partially reactive
soluble iron complexes with reduced activity or tendency to precipitate. These are generally sulphate complexes, and may be even further reduced in activity by the presence of chlorides. Sulphide complexes of iron are soluble, low in activity and difficult to precipitate.
Ferrous-ferric iron complexes are some times difficult to precipitate. Colloidal suspensions can be difficult to precipitate. Chlorination has a negative effect on iron precipitation by greatly reducing its activity or tendency to precipitate.

Birm is a catalyst which brings the iron in closer proximity with the dissolved oxygen and allows them to react to form the filterable ferric hydroxide which precipitates and remains in the Birm bed. Ferric hydroxide precipitates at a pH of about 3.0 and is more insoluble than ferrous hydroxide, which precipitates at a pH of about 7.0. it has been rather conclusively established that both oxygen and ferrous iron are absorbed on the Birm catalyst surface in high concentrations, thus accounting for this oxidation reaction.

Carbon dioxide is liberated in the above oxidation reaction and is theoretically equivalent to the iron precipitation. A more rapid reaction rate is observed in highly bicarbonate waters, and a slow reaction rate is typical in highly saline waters.

In distilled water to which is added 1.0 ppm of iron as ferrous sulphate and sufficient dissolved oxygen to complete the oxidation reaction to the filterable ferric hydroxide, Birm cannot complete the union of iron and oxygen because sulphuric acid, a strong acid, is liberated which blocks the reaction.

For good iron removal, the bicarbonate content or alkalinity of the water should be
at least twice as great as the combined sulphate-chloride content.

The minimum dissolved oxygen necessary for this catalytic oxidation reaction is 15% of the iron to be oxidised, as shown by the following table.

Iron	Dissolved Oxygen @ 320 F at sea level
Ppm	ppm	Cu. Ft. Air/1,000 gallons
0.1	0.015	0.007
1.0	0.15	0.067
2.0	0.30	0.133
5.0	0.75	0.333

The solubility of oxygen in water is dependent on both temperature and pressure, and some extent on nitrogen and other gases. The following table shows the effect of temperature and pressure on oxygen solubility.

Temperature		Oxygen in ppm
0F	0PSI	20 PSI	40PSI
32	14.7	34.7	54.7
50	11.3	26.7	42.2
60	10.0	23.6	37.4
70	9.0	21.5	3.5
140	3.6	3.4	13.3