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-۱, CW-۲ and CW-۳) filled with different filter media, each ۴ m۲ in area, planted with Arundo donax was operated for ۴ years for treating dairy farm wastewater. The vertical CW systems received high fluctuations in influent concentration and loads i.e. BOD (۲۶ to ۶۱۹ mg L-۱ and ۱.۵ to ۳۴ g m-۲ d-۱), TSS (۱۶۵ to ۶۴۳ mg L-۱ and ۹.۱ to ۲۴ g m-۲ d-۱), TP (۱۶ to ۴۹.۹ mg L-۱ and ۱.۲ to ۲.۷ g m-۲ d-۱) and NH۴-N (۲۴.۵ to ۷۶.۲ mg L-۱ and ۱.۳ to ۴.۲ g m-۲ d-۱) during the assessment period. Average annual removal rates showed fluctuations in removal of BOD (۷۰.۵ to ۹۲.۹%), TSS (۸۲.۵ to ۹۷.۵%), TP (۵۱.۱ to ۹۱.۹%) and NH۴-N (۳۴.۶ to ۶۹%). 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 NH۴-N) in the treated effluent showed noticeable decrease: ۴۳.۴ to ۱۶.۱ mg L-۱ for BOD; ۴۳.۳ to ۱۱.۷ mg L-۱ for TSS; ۱۷.۹ to ۳.۱ mg L-۱ for TP and ۳۳.۲ to ۲۲.۷ mg L-۱ for NH۴-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.

Keywords:

Vertical sub-surface flow constructed wetland , influent loads , dairy farm wastewater , Organic matter , BOD