Subsurface flow constructed wetlands are a bed of filter material with some reeds where wastewater flows either intermittently, vertically, or continuos, horizontally. The filter material is crucial for the treatment success and must meet these specs (according to DWA-A 262, German industry code):
[ul]
[li]permeability k[sub]fa[/sub]≈10[sup]−4[/sup]−10[sup]−3[/sup]ms[/li]
[li]grain size D[sub]10[/sub] from 0.2 to 0.4 mm[/li]
[li]uniformity coefficient U=D[sub]60[/sub]/D[sub]10[/sub]<5[/li]
[li]binding parts less than 2%[/li]
[/ul]
This mostly to ensure that the filter will not clog after a few years of operation.
Constructed wetlands are in principle an interesting technology in non industrialized countries. Suppose I can't go to a gravel plant and buy the filter material according to my specs, is there a way to make it from ordinary sand on site? Would this be simply a matter of sieving, or would I need additional steps (washing?)? How to adjust uniformity coefficient?
What machinery do I need, would I need to cart half a gravel plant to my site or would a sieve with exchangable sreens suffice?
This is not a question I face now in my work. This is just something that occured to me when reading up on CW - supposedly they are great wastewater treatment technology for remote, smallish communities in non-industrialized countries. However the quality of the filter material is, at least according to the literature I read so far, crucial and I'm sure many of these installations are built far from gravel plants.
[ul]
[li]permeability k[sub]fa[/sub]≈10[sup]−4[/sup]−10[sup]−3[/sup]ms[/li]
[li]grain size D[sub]10[/sub] from 0.2 to 0.4 mm[/li]
[li]uniformity coefficient U=D[sub]60[/sub]/D[sub]10[/sub]<5[/li]
[li]binding parts less than 2%[/li]
[/ul]
This mostly to ensure that the filter will not clog after a few years of operation.
Constructed wetlands are in principle an interesting technology in non industrialized countries. Suppose I can't go to a gravel plant and buy the filter material according to my specs, is there a way to make it from ordinary sand on site? Would this be simply a matter of sieving, or would I need additional steps (washing?)? How to adjust uniformity coefficient?
What machinery do I need, would I need to cart half a gravel plant to my site or would a sieve with exchangable sreens suffice?
This is not a question I face now in my work. This is just something that occured to me when reading up on CW - supposedly they are great wastewater treatment technology for remote, smallish communities in non-industrialized countries. However the quality of the filter material is, at least according to the literature I read so far, crucial and I'm sure many of these installations are built far from gravel plants.
