Sand Filter vs Multimedia Filter vs Activated Carbon Filter

Sand Filters, multimedia filters and activated carbon filters are three commonly used filtration devices in water treatment, each offering distinct characteristics and functions. Sand filters primarily retain suspended solids using a single type of filter media such as quartz sand, making them ideal for pretreatment to remove larger particles. Multimedia filters utilize multiple layers of media with varying particle sizes (e.g., anthracite, quartz sand, garnet) to achieve effective depth filtration and remove smaller and medium-sized particles. Activated carbon filters use granular activated carbon to adsorb organic contaminants, residual chlorine, and odors, enhancing the sensory quality and safety of the treated water. These three types of filters differ significantly in terms of media composition, filtration mechanism, and application scenarios. Selection should be based on specific water quality requirements.

1. Main Function and Design Purpose

The sand filter removes suspended solids, silt, and other large particulate impurities through physical retention, with the primary goal of reducing water turbidity. The multimedia filter utilizes multiple layers of filter media for collaborative filtration, enabling deep removal of suspended solids, colloids, and some organic substances, aiming to improve filtration accuracy and protect subsequent precision equipment. The activated carbon filter relies on chemical adsorption to effectively remove organic substances, residual chlorine, odors, and some heavy metals, focusing on improving the sensory indicators and safety of water quality. The three types of filters complement each other, addressing different purification needs.

2. Differences in Composition and Structure of the Filter Media  

The sand filter uses a single type of quartz sand (0.5-1.2 mm) as the filter media, forming a homogeneous filter bed. It primarily relies on surface filtration, with a typical filter bed height of 0.8-1.2 m. The Multimedia Filter uses a combination of multiple layers of filter media (such as anthracite + quartz sand + garnet) to achieve deep filtration through density and particle size gradients, with a total filter bed height of approximately 1.2-1.5 m. The activated carbon filter uses granular activated carbon (GAC) or coconut shell carbon as the filter media, relying on its porous structure to adsorb pollutants. The filter bed height needs to be between 1.0 and 1.8 m to ensure sufficient contact time. The three filters have distinct characteristics in filter media types, filtration methods, and filter bed designs.

3. Comparison of Filtration Mechanisms and Performance

The sand filter is primarily used to remove suspended solids larger than 20 μm, with a filtration accuracy of 20-50 μm and a turbidity removal rate of 60-80%. However, it is ineffective against residual chlorine and has a moderate pressure drop. The multimedia filter can remove suspended solids and colloids ranging from 5 to 50 μm, with a filtration accuracy of 5-10 μm and a turbidity removal rate of 85-95%. It is also ineffective against residual chlorine but has a lower pressure drop. The activated carbon filter efficiently removes organic substances, residual chlorine (over 99%), and odors through adsorption. It does not rely on filtration accuracy but has no direct effect on turbidity removal, requiring pre-filtration, and has a higher pressure drop.

4. Application

Sand filter, multimedia filter and Activated Carbon Filters are suitable for different water treatment scenarios. Sand filter is mainly used for desanding groundwater, pre-treatment of large suspended particles, primary filtration of irrigation systems, and purification of circulating water in swimming pools. Multimedia filters are suitable for high turbidity surface water treatment, pre-treatment of reverse osmosis systems, and deep removal of suspended solids in industrial wastewater. Activated carbon filters are good at treating pesticide residues, dechlorination and decolorization of drinking water, as well as odors from bitter and salty water. Each of the three types of filters has its own strengths, and suitable equipment should be selected based on the characteristics of water quality.

5. Comparison of Maintenance and Economic

There are significant differences in maintenance requirements between sand filters, multimedia filters and activated carbon filters, sand filters require water backwashing every 8-12 hours, with a filter material lifespan of 2-3 years and low energy consumption; Multi media filters require a combined backwash of water and gas every 24-48 hours, with a lifespan of 3-5 years and moderate energy consumption; The backwash cycle of activated carbon filters is the longest (72-168 hours), but the filter material needs to be replaced every 1-2 years, resulting in the highest overall cost. In terms of application scenarios, sand filtration and multimedia are suitable for removing suspended solids from industrial wastewater, while activated carbon is adept at treating pesticide residues, dechlorination and decolorization of drinking water (such as greenhouse water) and adsorption of bitter and salty water odors.

Filter selection should be based on the types of pollutants present. Sand filters are ideal for removing suspended particles with lower operational costs. Multimedia filters handle high turbidity and colloidal pollution while protecting downstream precision equipment. Activated carbon filters are essential for eliminating organic compounds, chlorine, and unpleasant odors. For complex water treatment needs, a combined system (e.g., sand + multimedia + activated carbon) is recommended to achieve optimal results.