In today's world, where water quality requirements are increasingly high, both domestic and industrial water use cannot do without efficient filtration equipment. The quartz sand filter, as a widely used filtration device, has become the preferred choice for many industries due to its excellent filtration performance and stable operation. Today, let's delve into the division of filter layers, laying methods, and key points of grain size selection in quartz sand filters, and uncover the mystery behind their efficient filtration.
The division of filter layers in quartz sand filters is like a meticulously designed architectural structure, with each layer having its unique function and role. Typically, the filter layer of a quartz sand filter consists of three parts: the bottom layer of large-grain cushion, the middle layer of quartz sand with a grain size of 2-4 mm, and the top layer of quartz sand with a grain size of 0.7-1.3 mm.
The bottom large-grain cushion layer acts like the foundation of a building, providing stability to the entire filter layer structure. Its primary function is to support the upper filter materials and prevent them from entering the water distribution system, thus ensuring the normal operation of the filter. The large-grain cushion layer has a relatively large grain size, which enables it to withstand significant water flow impact forces. This ensures that it will not be washed away or moved during the filtration process, providing a solid base for the entire filtration system.
The middle 2-4 mm grain size quartz sand layer is one of the core filtration layers of the quartz sand filter. The quartz sand in this layer has a moderate grain size and excellent interception capability. It can effectively remove larger particulate impurities from the water, such as silt and rust. When the water flows through this layer, these impurities are intercepted by the quartz sand particles, achieving preliminary water purification. The quartz sand particles in this layer are relatively large, with a higher porosity and lower water flow resistance. This allows the filter to operate normally at higher flow rates and effectively extends the filtration cycle.
The top 0.7-1.3 mm grain size quartz sand layer serves as the fine filtration layer of the quartz sand filter. The small grain size and low porosity of the quartz sand in this layer enable it to deeply intercept fine impurities in the water. It can effectively remove colloids, suspended particles, and other tiny particles from the water, further improving the purity of the water. The small quartz sand particles in this layer create a relatively higher resistance to water flow. Therefore, when designing the filter, it is necessary to reasonably control the water flow speed to ensure the filtration effect and operational efficiency of the filter.
Laying the filter layers is a crucial step in ensuring the filtration performance of quartz sand filters. The correct method can ensure the stability of the filter layer structure and fully utilize the filtration properties of quartz sand. Here are the specific steps for laying the filter layers in quartz sand filters:
Before laying the filter layers, it is essential to carry out preparation work. Firstly, all debris inside the filter should be thoroughly removed to ensure the cleanliness of the filter's interior. Then, check whether the water distribution holes and gaps in the water distribution system are unobstructed. Use the backwashing method to check if the water distribution system meets the design requirements. Only when the water distribution system works properly can the water flow evenly through the filter layers, achieving good filtration results.
Based on the top height of each layer of support material and filter material, draw a horizontal line inside the filter pool as a reference for the laying height. This step is of great importance as it ensures the accurate and uniform thickness of each layer of filter material, maintaining the stability of the filter layer structure. The marking of the horizontal line should be clear and accurate so that it can be checked and adjusted at any time during the laying process.
Carefully inspect the support materials of different grain size ranges (for three-layer filter pools, also check different types of support materials) and clean them according to their grain size ranges from large to small in preparation for spreading. During the cleaning process, pay attention to removing impurities and particles that do not meet the grain size requirements to ensure the quality of the support materials. The quality of the support materials directly affects the performance of the filter layer, so this step should not be taken lightly.
When laying the next layer of support materials, take care not to damage the water distribution system of the filter. The support materials to be loaded can be hoisted into the pool and then evenly spread out. Alternatively, fill the tank with water up to the top of the drainage trough, evenly sprinkle the materials into the water, and then drain the water, allowing the water surface to drop to the top of the layer. Use a shovel to evenly spread the materials. During the laying process, the spreader should not stand or walk directly on or over the support materials but should stand on a board and minimize operations inside the tank to prevent the movement of the support materials. The thickness of each layer of support materials should be accurate and uniform, leveled with a shovel or scraper to approach the horizontal plane, and the height should be consistent with the horizontal line marked as the laying height.
After the support materials with a grain size of 2-4 mm and below have been laid, rinse them with the upper limit of the filter's rinsing intensity. Before stopping the rinsing, gradually reduce the rinsing intensity to complete effective hydraulic grading, allowing lightweight materials to rise to the surface of the support materials. Then, discharge and scrape off the light substances. The purpose of this step is to remove lightweight impurities and particles that do not meet the grain size requirements from the support materials, ensuring the quality of the support materials and the performance of the filter layer.
After all the support materials have been laid in layers, evenly spread the planned amount of filter materials (including the light substances scraped off and fine particles smaller than the specified lower limit grain size) from the top of the pool towards the water surface. Then, clean and scrape off the light substances and particles smaller than the specified lower limit grain size. If the thickness of the filter materials does not reach the required value after the above operations, repeat the above steps until the requirement is met. For three-layer or dual-layer filter materials, only after rinsing the lower layer of filter materials and scraping off the light substances and particles smaller than the specified lower limit can another layer of filter materials be laid.
The selection of grain size for quartz sand filters is a core aspect of water purification. The grain size parameters directly affect the filtration efficiency, contaminant interception capacity, and operational stability of the equipment. Different grain sizes of quartz sand have different roles and characteristics in the filtration process. Therefore, it is necessary to make a reasonable selection of quartz sand grain size based on the specific water quality conditions and filtration requirements.
The smaller the grain size of quartz sand, the lower the porosity of the filter layer, and the stronger the interception capacity for fine impurities. For example, a fine-grain sand layer with a grain size of 0.5 - 0.8mm can effectively intercept colloids, suspended particles, and other tiny particles. It is suitable for advanced treatment of drinking water or precision filtration of industrial water. However, too small a grain size will increase the water flow resistance, leading to a decrease in filtration speed. It may even cause the sand layer to compact due to excessive pressure difference, affecting long-term operational efficiency. On the contrary, a coarse-grain sand layer with a grain size of 1.0 - 1.2mm has a high porosity and low water flow resistance. It is suitable for the preliminary treatment stage to remove large particulate impurities, such as turbidity removal of groundwater or primary filtration in wastewater treatment. However, its interception effect on fine particles is limited.
Grain size uniformity (i.e., the non-uniformity coefficient K80) is a key indicator. The ideal grain size distribution of quartz sand should be as concentrated as possible, avoiding a mixture of large and small particles. If the grain size difference is too large, small particles will fill the gaps between large particles, reducing the porosity of the upper part of the filter layer. Impurities are prone to clogging the surface layer, forming a "mud cake" phenomenon, which significantly shortens the filtration cycle. In contrast, a uniform grain size sand layer can form a more rational pore structure, allowing impurities to penetrate deep into the filter layer and enhancing the overall contaminant interception capacity. For example, quartz sand with K80≤1.5 can increase the contaminant interception capacity by more than 30%, extend the backwashing cycle, and reduce operating costs.
Backwashing is an essential part of the operation of quartz sand filters. Its purpose is to remove trapped impurities through water flow impact and sand particle friction, restoring the filtration performance of the filter materials. The selection of grain size directly affects the backwashing effect. Fine-grain sand layers are prone to residual impurities during backwashing due to insufficient water flow impact force, or they may form clumps due to mutual compression of sand particles. Coarse-grain sand layers require higher backwashing intensity; otherwise, it is difficult to dislodge impurities between particles. Generally, a grain size of 0.8 - 1.2mm combined with a backwashing intensity of 15 - 20L/(m²・s) can ensure cleanliness while reducing energy consumption. Moreover, a uniform grain size sand layer has a more stable expansion rate during backwashing, avoiding the occurrence of local "dead zones" and ensuring thorough regeneration of the filter materials.
Different water qualities have different requirements for the selection of quartz sand grain size. For high-turbidity water sources (such as surface water), it is preferable to use a coarse-grain sand layer with a grain size of 1.0 - 1.5mm. The large pores can quickly trap silt and other large particles, preventing the filter layer from clogging too early. For low-turbidity water sources (such as groundwater), a fine-grain sand layer with a grain size of 0.5 - 0.8mm can be used to enhance the interception capacity for colloids and organic matter. For special water qualities (such as iron and manganese-containing water sources), it is necessary to combine grain size with filter material modification. For example, using a quartz sand layer with a grain size of 0.6-1.0 mm in combination with a manganese sand cushion layer can achieve a balance between filtration precision and catalytic oxidation capacity.
As an efficient and stable filtration device, the quartz sand filter plays an important role in the field of water purification. The ingenious division of filter layers, the correct method of laying, and the rational selection of grain size are the keys to ensuring filtration performance. By gaining a deep understanding of these key points, we can better utilize the performance of quartz sand filters and improve the effect of water purification. With the continuous progress of technology and the increasing demands for water quality, quartz sand filters will surely be widely applied in more fields, providing cleaner and safer water for our daily lives and industrial production.
