A practical method for the restoration of clogged rural vertical subsurface flow constructed wetlands for domestic...

This paper presents a simple method for the restoration of clogged vertical subsurface flow constructed wetland by earthworm. Since clogging always takes place at the top layer, epigeic earthworm is suitable for restoration of the clogged wetland. Earthworm can not only loosen the substrate, but also transform 80∼90% of undissolved organic particles into dissolved matters. Accordingly, the accumulated solids in substrate with earthworm are 50% less than the one without earthworm. The wetland with earthworm removed 2∼5 percentage points more nitrogen and 12 percentage points more phosphorous for its better ventilation conditions, while 2 percentage points less COD because the generation of dissolved organic matter from undissolved organic particles by earthworm. In general, the influence of earthworm on the effluent quality of the wetland could be ignored. Hydrology of six full-scale clogged wetlands was restored by Eisenia foetida. The optimal strength of earthworm addition is 0.5 kg/m2, which spend RMB six yuan/m2, less than € 0.75/m2. No specific training is required for the staffs on this method; it takes 10 days to restore the clogged wetland.