Impact of the hydraulic loading rate on pollutants removal in tropical horizontal subsurface flow constructed wetlands

This study assessed the pollutant removal potential of horizontal subsurface flow (HSSF) constructed wetland systems under tropical conditions subjected to various hydraulic loading rates (HLRs). Three HSSF wetland units, each 1.4 m × 0.5 m × 0.6 m (length × width × height) in size, filled with 10–20 mm gravel as bed media, were used. Two beds were planted with a local emergent macrophyte; narrow-leaf cattail (Typha angustifolia), while the remaining served as a control without plants. All units were tested with synthetic wastewater mixed with septage sludge at different hydraulic loading rates (2.5–30 cm/day) over a period of six months. Results show that the planted HSSF wetland units removed pollutants substantially up to 25 cm/day HLR. Removal efficiencies at planted wetlands were over 80%, 44%, 96.5% and 96.1%, in comparison to unplanted wetland removals of 70%, 38%, 95.1% and 94.5% for five day biochemical oxygen demand (BOD5), total suspended solids (TSS), fecal coliform (FC) and total coliform (TC), respectively.