Effect of influent load fluctuation on the efficiency of vertical constructed wetlands treating dairy farm wastewater

Three vertical sub-surface flow (VSSF) constructed wetland (CW) systems (CW-1, CW-2 and CW-3) filled with different filter media, each 4 m2 in area, planted with Arundo donax was operated for 4 years for treating dairy farm wastewater. The vertical CW systems received high fluctuations in influent concentration and loads i.e. BOD (26 to 619 mg L-1 and 1.5 to 34 g m-2 d-1), TSS (165 to 643 mg L-1 and 9.1 to 24 g m-2 d-1), TP (16 to 49.9 mg L-1 and 1.2 to 2.7 g m-2 d-1) and NH4-N (24.5 to 76.2 mg L-1 and 1.3 to 4.2 g m-2 d-1) during the assessment period. Average annual removal rates showed fluctuations in removal of BOD (70.5 to 92.9%), TSS (82.5 to 97.5%), TP (51.1 to 91.9%) and NH4-N (34.6 to 69%). This shows that the removal of BOD is very sensitive to inlet load fluctuations in CWs. High inlet loads may confine good nitrification that affects ammonium-nitrogen removal while TP removal rate reduced when inlet TP loads reduced. The average concentration of the pollutants (BOD, TSS, TP and NH4-N) in the treated effluent showed noticeable decrease: 43.4 to 16.1 mg L-1 for BOD; 43.3 to 11.7 mg L-1 for TSS; 17.9 to 3.1 mg L-1 for TP and 33.2 to 22.7 mg L-1 for NH4-N. Thus from the outcomes of the current study, it can be concluded that the VSSF CW system may provide promising outcomes despite there is fluctuations in the influent loads.