Arsenic removal is a relatively new water treatment problem in Hungary, because after the EU connection the drinking water regulations are stricker. The permissible arseninc content in drinking water was reduced to 10 µg instead of 50 µg. As a result, the drinking water of hundreds of settlements has been placed the ”inadequate” category, in these water arsenic removal is required. The right phrase, instead of arsenic removal, is to reduce arsenic, since completely removing arsenic from water is analmost impossible task, buti t is not necessary.
In our groundwater, some of the arsenic is prensent as arsenate or trivalent arsenic. Removal of low valence arsenic from water is a very difficult task, so this is solved by first oxidizing the arsenic from three valences (As203) to five valences (As205). This is now easier to filter out with special technology, or bound to manganese, iron as iron arsenate can be removed with simple water purifier. This process is called the adsorption process. This adsoprtion os not as simple as it seems, because the chemical bonds of some natural arsenic (in raw water) are very difficult to break down, so the binding to metals does not take place.
Another method for arsenic removal is to use a catalytic arsenic removal charge. This is done by binding to the metals without oxidation, using a charge with an active surface, like iron hydroxide, manganese dioxide, or these combination. In both cases, hazardous waste is generated, but while the first case almost every backwash, in the second case only during every charge change.
The third known method is biological arsenic removal, but this is not described in more detail because this water treatment and this is used more in industrial wastewater.
Adsorptive arsenic removal:
This method od water treatment and purification is applied by adding a very strong oxidizing agent tot he water. This may be ozone, potassium permanganate, active chlorine or a combination of these. Arsenic is ready to bind to metals after oxidation. If the metal content of the raw water is not sufficient to bind arsenic, usually iron sulfate or iron chloride is added after the addition of the oxidizing agent or chemical. After the formation of the iron arsenate, the water is filtered on a multimedia gravel bed and removed from the water. Once the filter is saturated with these arsenic and metal precipitates, these flakes are backwashed out of the water purifier. In this case must taken care the sizing, the correct amount of oxidizing agent, the correct chemical, and the filtration rate of the multimedia gravel filter. If you overdose the chemical, it can occur in treated water, and if the surface of the filter is not selected well and the filtration speed is too high, we cannot catch the iron flakes on it. The other important task with this water treatment is wastewater treatment, as any backwash water leaving this equipmentis considered hazardous water.
Catalytic arsenic removal:
This is a much simpler task than the above water treatment and purification method, as it is used as iron remover.The big disadvantage of this system, however, is these charges are not cheap, and if the catalytic charge is chosen wrong, they can be depleted very quickly, depending ont he parameters of the water. There are several parameters of the water that we would not otherwise consider, but the charge is sensitive to it and deplete it quickly. Such as phosphate or silicate. The advantage of this water treatment system is that no permanent hazardous waste generated in the wastewater, as the arsenic binds to the surface of the catalytic charge cannot be removed by a simple backwash, only by special chemical process.