title: A two-stage subsurface vertical flow constructed wetland for high-rate nitrogen removal.
abstract: By using a two-stage constructed wetland (CW) system operated with an organic load of 40 gCOD.m(-2).d(-1) (2 m2 per person equivalent) average nitrogen removal efficiencies of about 50% and average nitrogen elimination rates of 980 g N.m(-2).yr(-1) could be achieved. Two vertical flow beds with intermittent loading have been operated in series. The first stage uses sand with a grain size of 2-3.2 mm for the main layer and has a drainage layer that is impounded; the second stage sand with a grain size of 0.06-4 mm and a drainage layer with free drainage. The high nitrogen removal can be achieved without recirculation thus it is possible to operate the two-stage CW system without energy input. The paper shows performance data for the two-stage CW system regarding removal of organic matter and nitrogen for the two year operating period of the system. Additionally, its efficiency is compared with the efficiency of a single-stage vertical flow CW system designed and operated according to the Austrian design standards with 4 m2 per person equivalent. The comparison shows that a higher effluent quality could be reached with the two-stage system although the two-stage CW system is operated with the double organic load or half the specific surface area requirement, respectively. Another advantage is that the specific investment costs of the two-stage CW system amount to 1,200 EUR per person (without mechanical pre-treatment) and are only about 60% of the specific investment costs of the singe-stage CW system.
authors.affiliation: Institute of Sanitary Engineering and Water Pollution Control, University of Natural Resources and Applied Life Sciences, Vienna (BOKU), Muthgasse 18, A-1190, Vienna, Austria. guenter.langergraber@boku.ac.at
authors.forename: Guenter
authors.initials: G
authors.lastname: Langergraber
authors.forename: Klaus
authors.initials: K
authors.lastname: Leroch
authors.forename: Alexander
authors.initials: A
authors.lastname: Pressl
authors.forename: Roland
authors.initials: R
authors.lastname: Rohrhofer
authors.forename: Raimund
authors.initials: R
authors.lastname: Haberl
mesh_terms: D009584:Nitrogen / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*; D053833:Wetlands
chemical_list: D009584:Nitrogen