title: Performance evaluation of different horizontal subsurface flow wetland types by characterization of flow behavior, mass removal and depth-dependent contaminant load.
abstract: For several pilot-scale constructed wetlands (CWs: a planted and unplanted gravel filter) and a hydroponic plant root mat (operating at two water levels), used for treating groundwater contaminated with BTEX, the fuel additive MTBE and ammonium, the hydrodynamic behavior was evaluated by means of temporal moment analysis of outlet tracer breakthrough curves (BTCs): hydraulic indices were related to contaminant mass removal. Detailed investigation of flow within the model gravel CWs allowed estimation of local flow rates and contaminant loads within the CWs. Best hydraulics were observed for the planted gravel filter (number of continuously stirred tank reactors N = 11.3, dispersion number = 0.04, Péclet number = 23). The hydroponic plant root mat revealed lower N and pronounced dispersion tendencies, whereby an elevated water table considerably impaired flow characteristics and treatment efficiencies. Highest mass removals were achieved by the plant root mat at low level: 98% (544 mg m⁻² d⁻¹), 78% (54 mg m⁻² d⁻¹) and 74% (893 mg m⁻² d⁻¹) for benzene, MTBE and ammonium-nitrogen, respectively. Within the CWs the flow behavior was depth-dependent, with the planting and the position of the outlet tube being key factors resulting in elevated flow rate and contaminant flux immediately below the densely rooted porous media zone in the planted CW, and fast bottom flow in the unplanted reference.
authors.affiliation: Department of Environmental Biotechnology, Helmholtz Centre for Environmental Research - UFZ, Permoserstr. 15, 04318 Leipzig, Germany. eva.seeger@ufz.de
authors.forename: Eva M
authors.initials: EM
authors.lastname: Seeger
authors.forename: Uli
authors.initials: U
authors.lastname: Maier
authors.forename: Peter
authors.initials: P
authors.lastname: Grathwohl
authors.forename: Peter
authors.initials: P
authors.lastname: Kuschk
authors.forename: Matthias
authors.initials: M
authors.lastname: Kaestner
mesh_terms: D001554:Benzene / Q000032:analysis / Q000737:chemistry; D002274:Carcinogens, Environmental / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D004787:Environmental Pollution; D052918:Environmental Restoration and Remediation / Q000379:methods*; D019015:Geologic Sediments / Q000737:chemistry; D005858:Germany; D060587:Groundwater / Q000737:chemistry*; D018527:Hydroponics; D055994:Limnology / Q000379:methods*; D008738:Methyl Ethers / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D008961:Models, Structural; D010578:Petroleum / Q000032:analysis; D010865:Pilot Projects; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D006109:Poaceae / Q000254:growth & development / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000032:analysis / Q000737:chemistry; D013045:Species Specificity; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D014877:Water Pollution, Chemical; D053833:Wetlands
chemical_list: D002274:Carcinogens, Environmental; D008738:Methyl Ethers; D010578:Petroleum; D000644:Quaternary Ammonium Compounds; D014874:Water Pollutants, Chemical; C043243:methyl tert-butyl ether; D001554:Benzene