Aeration column

Purpose and comparison of non-pressure and pressure aeration columns

1. Purpose of aeration columns
2. Types of aeration columns
3. Application of aeration columns for water purification from different types of contaminants
3.1 Application of aeration columns for water purification from iron
3.2 Use of aeration columns for water purification from organic substances 
3.3 Use of aeration columns for water purification from dissolved gases 
Conclusions and recommendations for the selection of aeration column type

1. Purpose of aeration columns

Aeration columns are designed for preliminary oxidation of water and its subsequent purification from various types of contaminants of organic and inorganic nature: dissolved iron, manganese (provided that pH is greater than 7.5 units), dissolved gases: ammonia, hydrogen sulfide, radon, carbon dioxide, organic substances: bacteria, viruses. The most widespread aeration columns and aeration of water in general have received in the treatment of water from wells and surface sources from iron and organics.

The principle of operation of all aeration columns is that air is supplied to the water, saturating it with oxygen. Then the water is fed into tanks of different volumes (depending on the required time for the oxidation reaction), in which the water mixes with air oxygen and oxidizes the substances that are in it (dissolved iron, organics, etc.), the remaining oxygen and dissolved gases are discharged through a hood or freely into the atmosphere. Compressors or blowers are used as the equipment that forces air into the water.

The advantage of water aeration over other methods of oxidation (chlorination, ozonation) is safety and reliability. And also there is no need to add various reagents to water and remove them from it.

Limitations of application. Along with the advantages in the application of aeration columns there are very significant limitations:

• Aeration is able to effectively purify iron provided that its content in water does not exceed 7-10 mg/l., and PMO (permanganate oxidizability) does not exceed 5 mg/l. (i.e. within the norm of SanPin 1074).
• Aeration is capable of oxidizing manganese if the pH level is greater than 7.5 units.
• Aeration is capable of oxidizing organic matter provided the MRL is less than 5 mg/l.

Aeration columns can be installed in cottages and on country plots. They are used in industrial production, rural and other farms. Can be used as an independent element of filtration or as part of a common water treatment system. Any water has various impurities in its composition and in different concentrations. This makes it quite dangerous for use. It may contain organic compounds, mechanical impurities, undissolved elements, dissolved gases, bacteria and viruses. All these impurities significantly degrade the condition of water. They can affect taste, color and odor. This is especially true for iron and manganese impurities and hydrogen sulfide. During thermal treatment, scaling may appear, in the case of the presence of hardness salts.

In any case, the water will not meet sanitary standards and should not be used. The method of aeration allows you to equalize the composition of water and even improve it. At the same time, aeration columns are used for filtration of drinking water, since they do not use reagents for purification. The systems are quite simple in operation. Most often, the method of aeration is used where the use of chemicals in filtration is not allowed or there is no need for high performance. That is, it is for drinking water, at food production facilities and so on.

2. Types of aeration columns

Depending on the presence of pressure, aeration columns are of two main types.

1. Pressure aeration columns (pressurized). In pressure aeration columns, the mixing of air oxygen with water takes place in closed vessels under pressure. As columns are used pressure columns made of fiberglass, stainless steel capable of withstanding pressure up to 10-15 bar.

The principle of operation of the pressure aeration column:

1. Water passes through a flow meter installed in the pipe. A water meter with a pulse output is usually used as a flow meter. The flow meter signals a flow switch, which starts a compressor or blower that forces air into the pipe.
2. The oxygenated water then enters the column, which is pressurized. In it the oxidation reaction of dissolved substances in water takes place. Excess oxygen is discharged through a vent valve installed on the head of the aeration column.
3. After the aeration column, water saturated with oxygen and oxidized substances goes to the next stage of purification, in which it is purified from oxidized substances (iron, manganese, hydrogen sulfide, organics, etc.) (see Fig. 1).

Fig. 1 Schematic diagram of pressure aeration column installation (1 - flow sensor, 2 compressor, 3 aeration column, 4 - deferrizer or sorption filter).

The special feature of pressure aeration columns is that the water in the column is pressurized. Therefore, no additional pumps and automatics are required for further water supply. Water pressure accelerates the oxidation reaction, which is also an advantage of pressure aeration columns over non-pressurized columns. The disadvantages include the fact that for a full-fledged oxidation reaction usually requires quite a long contact time of oxygen with dissolved substances from 20 minutes and more. Therefore, to ensure this time requires columns of very significant size, which increases their cost.

When installing pressure aeration columns, the installation site should be chosen carefully. Because the compressor is quite noisy. The system is installed in a freestanding building or in the basement. When increasing the capacity, you can add reagents. They will accelerate the chemical process and help to cope with more polluted water. But, of course, the environmental friendliness of the method is lost.

2. Unpressurized aeration columns. In unpressurized aeration columns, unlike pressurized ones, the reaction of air oxidation with water does not take place under pressure, but in open vessels under natural atmospheric pressure. As mixing tanks plastic, stainless steel, fiberglass, open concrete tanks and others are used.
Principle of operation of a non-pressurized aeration column. The principle of operation of a non-pressurized aeration column is similar to that of pressure aeration with the difference that oxidation does not take place under pressure, but in tanks with open access to air.

1. Water passes through a flow meter installed in a pipe. A water meter with a pulse output is usually used as a flow meter. The flow meter signals a flow switch, which starts a compressor or blower that forces air into the pipe.
2. The water-air mixture then enters an open container at the spout, where it mixes with air oxygen and oxidizes it. The gases dissolved in the water (radon, hydrogen sulfide, ammonia) are removed by means of a hood to the open atmosphere.
3. After aeration column water, under the action of natural pressure or with the help of feeding pump of the second lift is supplied to the next stage of purification, in which its purification from oxidized substances (iron, manganese, hydrogen sulfide, organics, etc.) takes place.

Fig. 2 Schematic diagram of non-pressure aeration column installation (1 - flow sensor, 2 - compressor, 3 - aeration tank, 4 - check valve, 5 - 2nd lift pump, 6 - filter).

The peculiarities of non-pressure aeration columns are longer contact with air (because the storage tanks are larger in volume), the possibility of more effective removal of gases dissolved in water: radon, ammonia, hydrogen sulfide and others, as well as additional contact with atmospheric air.

But at the same time, the time of oxidation and, consequently, filtration is greatly increased. Unpressurized aeration columns are used only in case of minor contamination with impurities or as one of the stages in the water treatment system. At high concentrations of contaminants, the aeration method will not do the job without additional intervention. Increasing the area of contact between water and oxygen is required to increase performance. This is not always convenient, because in this case a fairly large area is involved. And not all enterprises can accommodate oversized equipment.

3. Application of aeration columns for water purification from various types of contaminants

3.1 The use of aeration columns for water purification from iron
In borehole water a significant part of iron is in divalent (dissolved) form. Unpressurized or pressurized water aeration can be used to oxidize it.

Description of the technology.

Stage 1. Water passes through a pressure or non-pressure aeration column, in which air oxygen mixes with water, oxygen enters into oxidation reaction with iron, converting it from divalent (dissolved) to trivalent (undissolved) form. For effective oxidation of iron and manganese, it is necessary to ensure that the time of water residence in the aeration column is at least 30 minutes. Part of the oxidized undissolved iron begins to settle and precipitate already in the aeration column.
Stage 2. Water is fed to the deferrizator filter, where deoxidation and precipitation of residual iron and manganese takes place. The amount of iron, which is able to retain deferrizator is determined by the specific capacity of deferrization material and the iron content in the source water. As a deferrization material is used catalytic loads, which also accelerate the oxidation reaction (MFO, MJF, Ecoferox and others).
The undoubted advantage of this method of water deferrization is safety and no need to buy reagents for water deferrization.
Along with the advantages for this method there are certain limitations of application: iron in water not more than 3 mg/l PMO not more than 5 mg/l.

For deferrization, aeration columns are installed more often for domestic use. That is, on country plots. In industrial production, the oxidation process will run long enough, which is a little unprofitable. Although for pretreatment, this method is definitely suitable. Most often it is combined with other methods.

2.2 Application of aeration columns for water purification from organic substances.

Water from wells, rivers, lakes and other surface water bodies contains a significant amount of organic compounds.
At their insignificant content (permanganate oxidizability index of PMO should not exceed the norm of 5 mg/l. Aeration can be a very effective method of oxidation in combination with sorption carbon filters, where sorption of organic substances takes place).

Description of the technology.

Stage 1. Water enters the aeration column, similar to the 1st stage of deferrization. Then there is a preliminary oxidation of organic substances contained in water.
Stage 2. Water is supplied to the sorption carbon filter, in which sorption (extraction) of organic substances takes place on activated carbons. As activated carbons can be used birch or coconut activated carbon designed specifically for air or water purification.

When removing hydrogen sulfide from water, aeration is a very convenient way. But it is desirable to locate the columns away from populated buildings. The fact is that the accumulated gases come out through a special hole in the system. And it is hydrogen sulfide has the property to accumulate in the air. Therefore, at the location of the filtration system there may be an unpleasant odor and an accumulation of harmful gas in the air. This is not particularly dangerous, but it is still better not to be close to the equipment.

2.3 Use of aeration columns to purify water from dissolved gases

To purify water from dissolved gases: hydrogen sulfide, ammonia, radon, it is preferable to use non-pressure aeration of water in combination with a sorption carbon filter or reverse osmosis system. For removal of dissolved gases in water it is desirable to provide extraction of gases into the open atmospheric air.

Technology Description.

Stage 1. Water is saturated with air and enters at the spout into the tank of non-pressure aeration, where mixing and removal of gases dissolved in it takes place. It is desirable to remove gases from the tank by means of extraction into the open atmospheric air. For this purpose there is a spigot and a fan in the tank (similar to ventilation in houses).
Stage 2. Further water for purification from the residues of dissolved gases goes to the next stage on sorption carbon filters or reverse osmosis system to remove residual gases.
In conclusion, we present a table comparing the technical and economic characteristics of non-pressure and pressure aeration columns with recommendations for possible applications.

Table 1 - Comparison of pressure and non-pressure aeration characteristics

Conclusions and recommendations on selection of aeration column type. As can be seen from the comparative analysis table, unpressurized aeration columns are easier to operate, require less space for placement, and have lower cost. However, non-pressurized aeration columns are more reliable and effective in the presence of dissolved gases and iron in water.

The aeration method is very widespread and can be used in various applications for water filtration. Its advantage is in the environmental friendliness of the method, because the oxidizer is oxygen. At the same time, the installation costs are low. It is not necessary to buy reagents or install additional components. However, the oxidation process itself is quite slow, which significantly reduces productivity. In addition, there are limitations for the source water. There must be a certain acid-alkaline balance and the concentration of impurities must not exceed certain standards. If the requirements are not met, the efficiency of the method drops significantly.

Aeration plants can be automated. The initial source is used by any, although most often aeration is used to purify borehole water. The system does not require any special maintenance. It can be used at the stage of additional treatment. When strengthening the oxidation effect, you can add chemicals to the system. This will significantly accelerate the process, but is not suitable for drinking water treatment. However, it is necessary to supplement the system with accessories. Namely, a doser is needed to accurately feed chemicals into the water. The aeration method leaves the flow pressure and improves organoleptic properties, due to constant oxygenation. Installation of the system is fast and does not require certain skills.

Modern models have different equipment and appearance. All this depends on the manufacturer. When selecting equipment, first a chemical analysis of water is carried out and on the basis of these data is determined by the type of aeration and the model of equipment. It is important to comply with the requirements for operation and periodically rinse the feed material. If the requirements are not met, impurities can get into the treated water, deteriorating its quality.

Aeration columns can work effectively with any filtration elements. That is, if there is a need for additional treatment or pretreatment of water, then you can install any filters. For primary treatment, coarse filters are most often used, which help to retain mechanical contaminants, which significantly extends the service life of aeration columns.

All elements of the system must be resistant to corrosion and aggressive effects of the elements. Most often, the set already includes a feed material. It can be replaced with any other material over time. Aeration columns have a fairly long service life.