1. Physical Filtration and Support
Filter Media: Pebbles are commonly used as the support layer in multi-layer filters (such as rapid filters and slow filters). They are laid beneath fine filter media like sand and activated carbon to prevent the loss of fine filter material and evenly distribute the inflow. This prevents direct water impact from damaging the filter layer structure.
Support Function: Due to their hardness and wear resistance, pebbles can bear the weight of upper filter media, maintaining the structural stability of the filtration system.
2. Water Purification
Trapping Impurities: The gaps between pebbles intercept larger suspended solids, algae, silt, and other particles, serving as a pre-treatment stage that reduces the load on subsequent fine filtration.
Adsorption: The rough surface of pebbles possesses adsorption capacity, allowing them to bind certain organic matter, colloids, and other pollutants.
3. Aeration and Biofilm Carrier
Aeration Filters: In biological aerated filters (BAF), pebbles serve as biofilm carriers. Microorganisms colonize their surfaces to form biofilms, which degrade organic pollutants and ammonia nitrogen through biochemical processes.
Oxygenation: The voids formed by stacked pebbles facilitate air diffusion, increasing dissolved oxygen levels and promoting aerobic microbial activity.
4. Flow Regulation and Clogging Prevention
Uniform Water Distribution: In filter beds or wetland systems, the pebble layer evens out flow velocity, preventing short-circuiting or stagnant zones.
Preventing Compaction: In constructed wetlands or soil infiltration systems, the pebble layer prevents compaction of overlying soil or fine filter media, maintaining permeability.
5. Other Industrial Applications
Building Materials & Decoration: Pebbles are used in construction mortar, landscaping, and pavement surfacing.
Industrial Packing: Serves as packing material in chemical and metallurgical industries for gas or liquid distribution and dispersion.
Refractory Materials: Functions as thermal insulation or refractory auxiliary material in certain high-temperature industrial applications.
Application Examples
Water Treatment: Municipal water plants, wastewater treatment facilities, industrial effluent processing.
Constructed Wetlands: Vertical-flow or horizontal-flow wetlands in ecological restoration projects.
Aquaculture: Filters pond water quality and provides a growth environment for biofilms.
Landscape Water Circulation: Circulation and filtration systems for fountains and ponds.
Precautions
Grain Size Selection: Based on filtration precision requirements, pebbles of different grain sizes are typically layered (e.g., larger grains for the base layer, smaller grains for the upper layer).
Cleaning and Maintenance: Backwashing or replacement is required after prolonged use to prevent impurities from clogging pores.
Material Requirements: Select chemically stable materials (e.g., quartz-based pebbles with high SiO₂ content) to avoid dissolution that could affect water quality.
In summary, pebble filter media, with their durability, chemical stability, low cost, and versatility, serve as a crucial foundational material in water treatment and environmental protection projects.
