Solids accumulation in six full-scale subsurface flow constructed wetlands.
In this study, we evaluated the amount of accumulated solids in six different horizontal subsurface flow constructed wetlands (SSF CWs). We also investigated the relationship between accumulated solids and, on one hand, the wastewater quality and load and, on the other hand, the hydraulic conductivity of the granular medium. Aerobic and anaerobic biodegradability tests were also conducted on the accumulated organic matter. Experiments were carried out on full scale wastewater treatment systems consisting of SSF CWs with stabilisation ponds, which are used for the sanitation of small towns in north-eastern Spain. There were more accumulated solids near the inlet of the SSF CWs (3-57 kg dry matter (DM)/m2) than near the outlet (2-12 kgm DM/m2). Annual solids accumulation rates ranged from 0.7 to 14.3 kg DM/m2 year, and a positive relationship was observed between accumulation rates and loading rates. Most of the accumulated solids had a low level of organic matter (<20%). The results of the aerobic and anaerobic tests indicated that the accumulated organic matter was very recalcitrant and difficult to biodegrade. The hydraulic conductivity values were significantly lower near the inlet zone (0-4 m/d) than in the outlet zone (12-200 m/d). Although hydraulic conductivity tended to decrease with increasing solids accumulation, the relationship was not direct. One major conclusion of this study is that the improvement of primary treatment is necessary to avoid rapid clogging of the granular media due to solids accumulation.
Caselles-Osorio
Aracelly
A
Environmental Engineering Division, Hydraulics, Coastal and Environmental Engineering Department, Technical University of Catalonia, c/ Jordi Girona 1-3, Mòdul D-1, 08034 Barcelona, Spain.
Puigagut
Jaume
J
Segú
Emma
E
Vaello
Núria
N
Granés
Francesc
F
García
David
D
García
Joan
J
D000332:Aerobiosis; D001673:Biodegradation, Environmental; D017753:Ecosystem; D005374:Filtration; D013030:Spain; D014865:Waste Disposal, Fluid / Q000379:methods*; D014872:Water Movements; D053833:Wetlands