Influence of the stone organization to avoid clogging in horizontal subsurface-flow treatment wetlands

The major issue associated with horizontal subsurface flow constructed wetlands for wastewater treatment is clogging. This paper shows the research conducted to determine if a change in the design of the bed of stones and in the kind of these stones at wetlands contributes to prevent clogging. The research was carried out with real domestic wastewater. Two separate cases with different types of stones and different layouts were tested in a pilot channel. The changes incorporated in this experience against the designs typically used in subsurface wetlands have been implementing a plug flow, the use of cornerstones, the suitable stone organization and the design of a natural aeration circuit. An effective separation is obtained between the sludge falling to the bottom of the reactor, and the water above, which is oxygenated by the air drawn through the aeration circuit. The most significant result is the absence of silting in the transport of water. The natural aeration obtained was sufficient to prevent the growth of anaerobic processes from reaching a certain depth and hence no exopolymers are released which would otherwise facilitate anaerobic bacterial colonization of the stones to such a level that siltation appears.

► Organized stones bed in HSSF TW improves wastewater transport.
► The anti-clogging layout of stones bed and natural aeration circuit is confirmed.
► The exopolymers exudates by anaerobic bacteria induce clogging in HSSF.
► Natural aeration obtained is sufficient to prevent the growth of anaerobic process.