First, the physical characteristics of volcanic rock biological filter: 
 1. The appearance of the shape: no sharp grains, on the flow resistance, easy to plug, gas distribution uniformity of water distribution; surface roughness, biofilm speed, anti-microbial film easy to fall off when washing. 
 2. Porosity: porous volcanic rock is a natural cellular is the floc is the best growing environment. 
 3. Mechanical strength: the State quality inspection departments to 5.08Mpa, proven to stand the role of different hydraulic shear strength, life is much longer other media. 
 4. Density: medium density, anti-floating and not easy to run when washing materials can be energy saving. 
 Second, the chemical characteristics of volcanic rock biological filter: 
 1. Biochemistry Stability: volcanic rock biological filter anti-corrosion, inert, does not participate in biofilm in the environment of biochemical reactions. 
 2. Electrical and hydrophilic surface: the surface of volcanic rock with a positive charge of biological filter media, the growth of beneficial microorganisms fixing, hydrophilicity, adhesion of the biofilm quantity and speed. 
 3. The impact on biofilm activity: as biofilm carrier, volcanic biological filter media on the fixed microorganisms harmless, no inhibitory effect proved not affect microbial activity. 
 Third, the volcanic rock mechanical properties of biological water filter: 
 1, porosity: inside and outside the average porosity is about 40% of the water resistance, while compared with the same filter, filter required less, the same filter to achieve the desired objectives. 
 2, the specific surface area: surface area, high and noble openings, the contact is conducive to microbial biofilm formation and growth, maintain the microbial biomass more conducive to microbial metabolism of oxygen and nutrients needed and the metabolism of mass transfer of waste. 
 3, the filter shape and the water flow pattern: As the biological filter is not sharp volcanic rock grains, and the pore size is larger majority than the ceramic, so the use of flow resistance, saving energy consumption.