I. Basic Requirements
Due to the low efficiency and high investment of commonly used river pollution treatment techniques such as aeration and biofilm, which are difficult to scale up for widespread application, constructed wetlands offer advantages like large buffer capacity, easy management, and low infrastructure and operational costs, making them the preferred technology for treating polluted river water.
In the artificial wetland wastewater treatment process, the selection of media is a crucial step: on one hand, it provides a carrier and nutrients for the growth of aquatic plants; on the other, it offers a stable surface for microbial growth. Moreover, media can remove pollutants from wastewater physically and chemically, such as up to 87% of phosphorus in artificial wetlands, which can be removed through precipitation or adsorption. Therefore, volcanic rock particles with good permeability, a large specific surface area, abundant sources, and low cost are chosen as the media for the artificial wetland system.
Section 2: Volcanic Rock Filler Features
1. Beneficial for microbial attachment and biofilm formation.
2. Excellent retention of nutrients required by microorganisms, facilitating their reproduction and slow-release in wetlands.
3. Resists color fading after water immersion.
4. Features mechanical strength.
5. In terms of volume and shape, the packing material provides as much surface area as possible.
6. In terms of biological stability, the packing material should be inert, capable of resisting biological corrosion of the packing material, and not participate in biological chemical reactions during biological treatment. In terms of chemical stability, the packing material should exhibit inertness to chemical reactions occurring in the environment and possess resistance to chemical corrosion. In terms of thermodynamic stability, the packing material should be inert to changes in surrounding temperatures.
7. For the requirements of artificial wetland functions, matrices with certain chemical compositions can be selected. These matrices can be natural substances, recyclable solid waste, or artificially synthesized materials containing special components, as well as mixed materials with varying proportions.
8. Hydrophilicity, hydrophobicity, and surface electrification. Hydrophilic microorganisms tend to adhere and immobilize on hydrophilic packing surfaces, while hydrophobic packing is beneficial for hydrophobic microorganisms to attach to its surface. The hydrophilicity, hydrophobicity, and electrical properties of the packing surface can also be achieved through modification of the packing surface or directly during the packing processing.
9. Must have porosity and surface roughness.
10. Impact on Biofilm Activity. As a biofilm carrier, it must be harmless and non-inhibitory to the attached microorganisms, and cannot significantly affect the biological activity of the attached microorganisms.
11. Reusability. Economically speaking, the matrix should be reusable, especially when used on a large scale, which holds significant importance.
