biological filter of volcanic rocks structural features: 1)microbial chemical stability 2)electrical and hydrophilic 3)has the impaction for the biological
pebbles(gravel) filter pebble filter material1.for water treatment2.has big pore,long action cycle3.fast percolation speed
refine anthracite 1can absorb suspended debris,floc 2in the state of Gengon angular 3stable physical chemical properties 4high strength