Avoiding clogging in constructed wetlands by using anaerobic digesters as pre-treatment

The main operational problem of subsurface flow constructed wetlands (CWs) is clogging of granular medium, a phenomenon related to the accumulation of different types of solids that lead to a reduction of the infiltration capacity of the gravel bed. It is generally accepted that the application of a good wastewater pre-treatment is essential for the long-term operation of subsurface flow CW. Anaerobic digesters (ADs) could help to the aim of clogging prevention. Two combined AD-CW treating either municipal or winery wastewater were designed and monitored for trough performance and efficiency parameters, solids accumulation and hydraulic conductivity, over a long term period. CW operated at high organic loading rates in terms of TCOD and BOD5 while suspended solids loading rates and solids accumulation in CW were lower. In turn, CW maintained an adequate hydraulic conductivity and low rates of solids accumulation.