Aeration to Promote Nitrification in Constructed Wetlands

ISSN： 0959-3330

Source： Environmental Technology, Vol.20, Iss.1, 1999-01, pp. : 69-75

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Abstract

As part of a three year study of the use of reed beds for the treatment of wastewater, two pilot scale constructed wetlands (30m × 5m), one planted with Phragmites australis and the other serving as an unplanted control, were used to treat primary domestic sewage. This paper describes an experiment conducted to test the hypothesis that increasing available oxygen by aeration of the wastewater in the treatment beds could increase nitrification, and hopefully nitrogen removal rates. Prior to aeration, the influent nitrogen load in the wastewater passing through the beds was reduced by approximately 45% and 10% in the planted and control beds respectively. With aeration of the wastewater as it passed through each bed, nitrogen removal was approximately 51% and 20% for the planted and control beds respectively. High rates of nitrification were recorded for the planted bed with aeration, but removal of nitrogen by denitrification was limited, probably because of the absence of a suitable carbon source (indicated by low BOD₅ concentrations). High nitrification rates were not recorded in the unplanted control bed. The higher BOD₅ concentration measured in this bed may have caused increased competition for available oxygen between heterotrophic bacteria and the relatively slow-growing nitrifying bacteria, resulting in lower rates of nitrification but more efficient denitrification.