Discussion on the characteristics of various filter media in filter tanks

As the core treatment unit of a water plant, filter media plays a crucial role in the filtration process. The commonly used filter media include quartz sand, granular activated carbon, garnet, titanium iron ore, ceramic particles, etc. How to choose a suitable filter media depends on the water quality of the raw water. Below, based on experience, we will discuss the principles and characteristics of various filter media.

1、 Anthracite filter material;
Anthracite filter material is made from selected, crushed, and twice screened anthracite coal. It has a good glossiness, spherical appearance, high mechanical strength, excellent compressive performance, stable chemical properties, no toxic substances, and wear resistance. At the same time, the surface of the anthracite filter material is rough, has good adsorption capacity, and has a large porosity (≥ 52%).
The use of anthracite filter material in the filter has the following advantages: firstly, due to the strong adsorption capacity of anthracite filter material, it can effectively intercept organic impurities in water, provide a large amount of growth and reproduction space for microorganisms, thereby degrading organic matter in the influent and nitrifying NH4+- N. Secondly, the mechanical strength and compressive performance of anthracite filter media are good, and they can withstand high-intensity flushing pressure during the filtration process. In addition, anthracite filter media can not only be used for single-layer filter media filtration, but can also form double-layer or three-layer filter media filtration processes, allowing the entire filter bed to be fully utilized.
2、 Quartz sand filter material has the following advantages:
1. No impurities, compressive and wear-resistant, high mechanical strength, and stable chemical properties.
2. Strong pollution interception ability, high filtration accuracy, high efficiency, and long service life.
3. Suitable for single-layer and double-layer filters, filters, and ion exchangers.
4. By optimizing the design of filter media and filters, the adaptive operation of the filters has been achieved. The filter media has strong adaptability to the concentration of raw water, operating conditions, pre-treatment processes, etc.
5. During filtration, the filter bed automatically forms an upper sparse and lower dense state, which is conducive to ensuring the effluent quality under various operating conditions; The filter material is fully dispersed during backwashing, resulting in a good cleaning effect.
6. It can effectively remove suspended solids in water and has a significant removal effect on pollutants such as colloids, iron, organic matter, pesticides, manganese, bacteria, viruses, etc.
However, quartz sand filter materials also have some drawbacks:
1. Difficulty in backwashing operation. If the backwashing intensity is too high, it will bring out small particles, causing loss of quartz sand filter material; However, if the backwash intensity is too low, it cannot loosen the larger quartz sand filter material in the lower part. Prolonged use may lead to quartz sand compaction and worsen the filtration condition.
Due to the uneven particle size of quartz sand filter material, fine quartz sand filter material particles may appear. These fine particles will concentrate on the surface of the filter layer, so the filtered dirt will accumulate on the surface of the filter layer, increasing the head loss too quickly and shortening the filtration cycle.
3、 The application of granular activated carbon in filtration tanks mainly has the following advantages:
1. The granular activated carbon filter can effectively remove harmful substances and microorganisms in water, such as toxic gases and organic matter.
2. Through the strong adsorption capacity of activated carbon, not only can suspended solids in water be effectively filtered to obtain water with lower turbidity, but water in sludge can also be removed to obtain sludge with lower water content.
3. The granular activated carbon filter material has developed pore structure and good adsorption performance, high mechanical strength, easy to regenerate, and low cost.
However, granular activated carbon filters also have some drawbacks:
1. The bacterial count in the granular activated carbon filter is high, especially when the influent water quality changes. The effluent can often detect a high bacterial count, which may affect the water quality.
2. Due to the accumulation of suspended solids filtered out by activated carbon between the filter layers, the water resistance of the filter layer will gradually increase. If not backwashed in a timely manner, it can cause excessive accumulation of sludge, change the structure of the filter material layer, and even cause "rupture", resulting in a short circuit of the filtered water and a deterioration of the effluent quality.
4、 As a new type of mineral filter material, garnet filter material has strong competitiveness and broad application prospects in water purification treatment. It is processed from natural silicate mineral garnet with stable chemical properties. The content of garnet mineral is ≥ 95%, with a color of brown and light yellow green, a specific gravity of 3.6-3.8, and a capacity of 2.0-2.2.
Advantages of pomegranate filter material:
1. Garnet filter material has stable performance, low price, and can replace expensive manganese sand, diamond sand filter material, and other imported raw materials.
2. It has developed pore structure and good adsorption performance, high mechanical strength, easy repeated regeneration, and low cost.
3. The specific gravity is between 4.1-4.4g/cm3, and its significant characteristics enable it to withstand the buoyancy of water and strong flushing pressure. It is mainly used in the position of the bottom filter material in multimedia filtration systems and plays a crucial role in the water quality of the filtration process.
4. Strong corrosion resistance, with a solubility of only 1% in acid and alkali, making it suitable for treating various types of water quality such as acidic, alkaline, and neutral.
Disadvantages of garnet filter material:
1. Uneven particle size may lead to uneven water flow velocity and affect filtration efficiency.
2. Wear and tear may occur during use and require regular replacement.
5、 Titanium iron ore is an oxide mineral of iron and titanium, also known as titanium magnetite, and is the main ore for extracting titanium and titanium dioxide. It has a gray to black appearance, and the crystals are generally plate-like, gathering together to form block or granular shapes. 
The main advantages of using titanium iron ore as filter material are:
1. Ilmenite has a well-developed pore structure and good adsorption performance, with high mechanical strength, which enables it to withstand high-intensity flushing pressure in the filtration process, ensuring water quality.
2. At the same time, its specific gravity ranges from 4.1 to 4.4 g/cm3, and its significant characteristic allows it to stably suspend in water and not be easily washed away.
In addition, titanium iron ore has strong corrosion resistance and is suitable for treating various types of water quality such as acidic, alkaline, and neutral.
There are some drawbacks to ilmenite ore:
1. Uneven particle size may lead to uneven water flow velocity and affect filtration efficiency.
2. Wear and tear may occur during use and require regular replacement.
3. For fine-grained ilmenite, the sorting ability is poor and the recovery rate is low.
6、 Characteristics of ceramic filter material;
The ceramic filter material is mainly made of clay, clay, and viscous solvents, and is processed through steps such as ball milling, screening, and calcination. Its characteristics include a hard surface, multiple micropores inside, and high porosity, which provide abundant growth space for microorganisms.
The advantages of ceramic filter media are mainly reflected in the following aspects: firstly, due to its large opening rate and pore size, it can effectively intercept organic impurities in water, provide a large amount of growth and reproduction space for microorganisms, and thus play a degradation role in organic matter in influent and nitrification of NH4+- N. Secondly, the surface of ceramic filter media is rich in micropores, with a large specific surface area, easy membrane formation, and high biomass. It has a good removal effect on NH3-N and COD, strong interception ability, and therefore, the treated effluent water quality is high. In addition, the pore distribution of the filter material is uniform, and the mesopores and macropores suitable for microbial growth are uniformly distributed, which helps to overcome the problems of large head loss, blockage, and compaction caused by uneven pore distribution in the filter material layer.
However, ceramic filter materials also have some drawbacks: compared with activated carbon, ceramic particles do not have the same large specific surface area as activated carbon, and the internal surface area composed of micropores is significantly smaller than activated carbon; During operation, more frequent backwashing and replacement of filter media may be required to maintain its treatment efficiency.
The above is the principle and characteristics of using various filter media in the filter tank of the water plant. Generally, when considering the filter media, quartz sand is used as the filtering material in the design, which has high cost-effectiveness. However, based on experience, the selection of filter media should still be based on the condition of the raw water.