Performance of experimental horizontal subsurface flow constructed wetlands fed with dissolved or particulate organic matter

In this study, the effect of the influent type of organic matter (dissolved or particulate) on the efficiency of two experimental horizontal subsurface flow constructed wetlands (SSF CWs) was investigated. The SSF CWs’ surface area was 0.54 m2 and the water depth was 0.3 m. They were monitored for a period of 9 months. One of the SSF CWs was fed with dissolved organic matter (glucose, assumed to be readily biodegradable), and the other with particulate organic matter (starch, assumed to be slowly biodegradable). The removal efficiency of the systems was tested at different hydraulic retention times (HRTs) in the presence or absence of sulphate. The removal efficiency of the COD was not different in the two systems, reaching eliminations of around 85% in the presence of sulphates and around 95% in their absence. Ammonia N removal was low in the two SSF CWs; the system fed with glucose generally had statistically significant higher removal (45%) than the one fed with starch (40%). Ammonia N removal was more affected by the HRT than by the presence or absence of sulphates. Hydraulic conductivity measurements showed that it was lower near the inlet of the SFF CW fed with glucose, probably connected to the fact that there was a more substantial development of the biofilm. The results of this study suggest that SSF CWs are not sensitive to the type of organic matter in the influents, whether it is readily (like glucose) or slowly (like starch) biodegradable, for the removal of COD.