To have good water quality in your swimming pool, you need to use swimming pool water treatment equipment. The filtration system in water treatment is a more crucial component, and the filtration medium is an essential part of this system. Commonly used filter media are quartz sand and diatomite, below, we will introduce these two types of water treatment media to help you understand their advantages and disadvantages.
Step 1: Analysis of quartz sand and diatomaceous earth for filter materials
Quartz sand
Quartz sand is a kind of filtration medium in swimming pool water treatment equipment, and the filtration method used here is deep filtration. When the swimming pool water passes through the quartz sand layer, the suspended debris in the pool water is blocked and adsorbed by the quartz sand as it passes through the upper layer. The suspended matter stays on the upper layer of the quartz sand, and the suspended matter accumulates on the upper layer to form a filter membrane, which also plays a filtering role. Quartz sand filtration purifies swimming pool’s water quality though this repeated filtration method .
Diatomite
With the development of technology, diatomaceous earth has also been widely used in swimming pool water treatment. In the past, diatomaceous earth was often used in water treatment for beverage, wine, medicine, and other applications. Diatomite naturally has the characteristics of porosity, can naturally perform effective interception and adsorption function, not only can clean the suspended matter in the pool water, but also can remove the organic matter, sporozoon and bacteria in the water to a certain extent. The filtration effect is better than that of quartz sand to a certain extent. However, the price and cost of diatomite are relatively high.
Step 2: Comparative analysis of the advantages of quartz sand and diatomite
Quartz sand and diatomaceous earth have advantages and disadvantages, quartz sand is produced in large quantities, its production is convenient, the price is low, and it’s easy to replace. Although there are substantial reserves of diatomite around the world, it’s mining is more challenging, the quality of the mined products is also relatively poor, and the price is relatively expensive. It’s a hassle to replace. Quartz sand filtration has been used and improved for more than 50 years, but the use of diatomaceous earth has been relatively recent. How to choose the filtration medium of the swimming pool water treatment equipment, this should be based on the requirements of water treatment and the scope of application. Usually large and small swimming pools are filtered with quartz sand, and some villa swimming pools and high-standard swimming pools use diatomaceous earth filtration. In contrast, diatomite filtration technology can effectively remove bacteria, require less chemical agents, partly control organic matter and ammonia nitrogen, and make the swimming pool water into a virtuous cycle treatment method, suitable for high-grade swimming pool circulating water treatment. Sand tank filtration is suitable for any swimming pool and has a wide range of applications.
Step 3: Comparison of water saving of diatomaceous earth and quartz sand filtration in swimming pools
For example: If a swimming pool contains an indoor standard swimming pool and a leisure swimming pool, the two swimming pools share a set of swimming pool water treatment equipment system, the pool surface area is about 2000㎡, the total volume is about 3500m³, the cycle period is 6h, the total circulation water is about 600m³/h, The circulation mode adopts the counter-current circulation mode recommended by FINA with the overflow of the bottom part of the water.
Water saving performance comparison
The water consumption of the swimming pool is reflected in that the supplementary water is generally composed of the water surface evaporation of the pool water, the washing water of the filtration equipment, the sewage water of the swimming pool and the water taken away by the swimmer’s body, etc., among which the washing water of the swimming pool filtration equipment accounts for the majority, about 80% of the total supplementary water. According to the annual average daily swimming pool supplementary water is 5% of the total volume of the swimming pool (5%-10% stipulated in the swimming pool design manual), using a diatomite filter , compared to a pool sand filter, can conservatively estimated reduce the filtration equipment flushing water 85%, reduce the pool supplementary water 80%×85%=68%. Daily water saving: 3500m³/d×5%×68%=119 (m³/d), conservative estimate of annual savings: 119m³/d×365d×4.2 yuan /m³÷10000=18.2 (10,000 yuan).
Comparison of supplemental water
The requirement of 5%-10% of the daily supplemental water is determined on the premise of quartz sand filtration, in order to dilute the chemicals added to the pool water and the resulting increase in TDS. And it is stated in the specification that “it is a reference value in the case of incomplete information”. However, because of the high filtration accuracy of the diatomite filter and the use of the ozone system, the dosage of chemical agents is greatly reduced, so the amount of supplementary water should be reduced according to the actual situation. According to the recommendations of the World Health Organization, 30L of supplementary water per person can be used. According to the statistics of the operation project, the maximum daily water recharge is 0.03m³/ person ×1500 people /d=45 (m³/d). The use of diatomite filter can reduce the pool water recharge by 68%, and the remaining 32% pool water recharge: 3500m³/d×5%×32%=56 (m³/d), so the control of the chemicals in the pool water and the TDS rise caused by it is still safe and reliable, and the diatomite filter should slightly increase the number of backwashing times during the peak period, and the amount of supplementary water will also appropriately increase.
Step 4: In-depth exploration of diatomite filtration in swimming pool water treatment
Structural characteristics of diatomite
The structure of diatomite is characterized by porosity, and it is easy to filter out small dirt in the filtration, so the filtration accuracy in the swimming pool water treatment is higher than that of the use of the pool sand filter. According to the practical effect, the filtration accuracy of the surface diatomite is more than 10 times that of sand filtration, and the water quality after purification and filtration is clear and transparent. Due to the high filtration accuracy of diatomite, it can also filter out some bacteria, viruses and microorganisms in the pool water treatment, so the use of disinfection agents is reduced in the disinfection process. For sand filtration, it is necessary to add flocculant to the pool water before filtration to improve accuracy, whereas the diatomite filter does not require adding flocculant, so the use of chemical agents is reduced, making the swimming environment more suitable.
Swimming pool water treatment equipment diatomite filtration process
Diatomite filtration process: pre-coating → circulating filtration → backwashing. Pre-coating refers to the diatomaceous earth is applied to the surface of the filter element before circulating filtration to form a 2-3mm thick filter film. The diatomite slurry prepared in the pre-coated bucket is pumped into the filter by the pump, and part of the diatomite returns to the pre-coated bucket with water. As the diatomite is gradually bridged on the surface of the filter element to form a filter membrane, the diatomite in the subsequent pre-coated liquid is constantly trapped, and the water is generally clear after about 5-10min, that is, the pre-coated film is completed. Rear circulation filtration and backwashing are basically the same as sand filtration.
Advantages of diatomaceous earth filter
- Compared with the same water treatment pool sand filter, diatomite filter area is large, small equipment volume, small quality, easy installation, small footprint, small backwash water.
- The use of less chemicals, only need to add disinfectant drugs, no need to add flocculants, reduce the supporting equipment.
- High filtration accuracy, can filter all kinds of impurities above 1μm, the turbidity of the effluent is close to 0, resulting in clear and transparent water quality. Can filter coliform, cryptosporidium, Giardia and other bacteria, viruses. The experimental results show that the filtration rate of bacteria is greater than 99.5%, and that of virus is greater than 85%.
- The backwashing strength of the diatomite filter is the same as the filtering strength; More water and energy efficient than pool sand filters.
Conclusion
Diatomaceous earth filtration technology has gradually been introduced into the swimming pool water treatment equipment, and achieved good water purification effect, the amount of injection is small, the equipment room area required is small, less heat loss and other characteristics, can reduce infrastructure investment can also reduce operating costs, considerable economic benefits, but the diatomaceous earth filter price is higher. However, with the increasing use of diatomaceous earth filtration and control technology, it is expected that its application in swimming pools will become more extensive. Each filtration method has its advantages and is suited to different types of applications based on the specific requirements for particle size removal, flow rate, and cost.
