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.