Effect of artificial aeration on tertiary nitrification in a full-scale subsurface horizontal flow constructed wetland

Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment

“…The general efficacy of the approach towards enhancing nitrification has been demonstrated predominately at pilot scale for a range of feed water types including synthetic wastewater [10,11], heavily polluted river water [12], and municipal secondary sewage [8]. Illustrations of the efficacy of the technology have also been presented at full-scale in terms of the treatment of landfill leachate [13], industrial wastewater [14], and tertiary treatment of municipal sewage [2]. In the latter, hydraulic loading rates are considerably higher than those utilised elsewhere with typical rates of 0.2-0.9 m/d reported in the UK [15] compared to 0.001-0.049 m/d for the sites treating industrial wastewaters [14].…”

“…However, traditional HSSF beds are often hydraulically loaded at rates that cause anoxic/anaerobic conditions to predominate with the associated sub-surface oxygen limitation (sub 0.5 mg/L) restricting observed nitrification rates in full scale tertiary HSSF CWs to 0.05-0.22 gNH 4 + -N/m 2 /d [2]. This type of operation and loading rates are generally insufficient to meet future discharge targets within typically limited available land areas.…”

“…The same study demonstrated near complete nitrification (99% removal) without negatively impacting on solids and organic matter removal efficiencies. Aeration also appeared to increase hydraulic conductivity, and improve hydraulic efficiency in the aerated bed under sub-surface flow, resulting in a more efficient reactor [2]. A paucity of information remains around full-scale tertiary systems treating variable flows and loads including storm flows and the inherent seasonal variations in wastewater characteristics and temperatures.…”

“…Ammonia concentrations feeding the tertiary beds can reach as high as 40 mgNH 4 + -N/L on sites that previously had no requirement to remove ammonia and, as such, ammonia-loading rates can significantly exceed those previously considered. To illustrate, non-tertiary cases have reported loading rates in the range 0.9 gNH 4 + -N/m 2 /d to 6.9 gNH 4 + -N/m 2 /d [8,13], which compares to a maximum rate of 10.1 mgNH 4 + -N/m 2 /d observed during an assessment of the initial stages of operation of a full scale tertiary aerated wetland [2]. The same study demonstrated near complete nitrification (99% removal) without negatively impacting on solids and organic matter removal efficiencies.…”

“…This type of operation and loading rates are generally insufficient to meet future discharge targets within typically limited available land areas. Across the full spectrum of applications for constructed wetlands a number of innovative adaptations have been developed to overcome the oxygen limitation including decreasing the depth of the bed [3]; recirculation of the treated effluent [4]; batch loading including traditional vertical flow systems [5] and adaption to horizontal flow beds, i.e., tidal flow [6]; and forced (artificial) aeration of traditional vertical flow systems [7], flooded vertical flow systems [8], or horizontal flow beds [2,9]. The general efficacy of the approach towards enhancing nitrification has been demonstrated predominately at pilot scale for a range of feed water types including synthetic wastewater [10,11], heavily polluted river water [12], and municipal secondary sewage [8].…”