Performance evaluation of different horizontal subsurface flow wetland types by characterization of flow behavior, mass removal and depth-dependent contaminant load.

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.

Dynamics of Fe(II), sulphur and phosphate in pilot-scale constructed wetlands treating a sulphate-rich chlorinated hydrocarbon contaminated groundwater.

Long-term investigations were carried out in two pilot-scale horizontal subsurface flow constructed wetlands (planted and unplanted) with an iron-rich soil matrix for treating sulphate-rich groundwater which was contaminated with low concentrations of chlorinated hydrocarbons. The temporal and spatial dynamics of pore-water sulphide, Fe(II) and phosphate concentrations in the wetland beds were characterized and the seasonal effects on sulphide production and nitrification inhibition were evaluated. The results demonstrated that the pore-water sulphide concentrations gradually increased from less than 0.2 mg/L in 2005 to annual average concentrations of 15 mg/L in 2010, while the pore-water Fe(II) concentrations decreased from 35.4 mg/L to 0.3 mg/L. From 2005 to 2010, the phosphate removal efficiency declined from 91% to 10% under a relatively constant inflow concentration of 5 mg/L. The pronounced effect of plants was accompanied by a higher sulphate reduction and ammonium oxidation in the planted bed, as compared to the unplanted control. A high tolerance of plants towards sulphide toxicity was observed, which might be due to the detoxification of sulphide by oxygen released by the roots. However, during the period of 2009-2010, the nitrification was negatively impacted by the sulphide production as the reduction in the removal of ammonium from 75% to 42% (with inflow concentration of 55 mg/L) correlated with the increasing mean annual sulphide concentrations. The effect of the detoxification of sulphide and the immobilization of phosphate by the application of the iron-rich soil matrix in the initial years was proven; however, the life-span of this effect should not only be taken into consideration in further design but also in scientific studies.

Bioremediation of benzene-, MTBE- and ammonia-contaminated groundwater with pilot-scale constructed wetlands.

In this pilot-scale constructed wetland (CW) study for treating groundwater contaminated with benzene, MTBE, and ammonia-N, the performance of two types of CWs (a wetland with gravel matrix and a plant root mat) was investigated. Hypothesized stimulative effects of filter material additives (charcoal, iron(III)) on pollutant removal were also tested. Increased contaminant loss was found during summer; the best treatment performance was achieved by the plant root mat. Concentration decrease in the planted gravel filter/plant root mat, respectively, amounted to 81/99% for benzene, 17/82% for MTBE, and 54/41% for ammonia-N at calculated inflow loads of 525/603 mg/m(2)/d, 97/112 mg/m(2)/d, and 1167/1342 mg/m(2)/d for benzene, MTBE, and ammonia-N. Filter additives did not improve contaminant depletion, although sorption processes were observed and elevated iron(II) formation indicated iron reduction. Bacterial and stable isotope analysis provided evidence for microbial benzene degradation in the CW, emphasizing the promising potential of this treatment technique.

Performance evaluation using a three compartment mass balance for the removal of volatile organic compounds in pilot scale constructed wetlands.

To perform a general assessment of treatment efficiency, a mass balance study was undertaken for two types of constructed wetlands (CWs), planted gravel filters and plant root mat systems, for treating VOC (benzene; MTBE) polluted groundwater under field conditions. Contaminant fate was investigated in the respective water, plant, and atmosphere compartments by determining water and atmospheric contaminant loads and calculating contaminant plant uptake, thereby allowing for an extended efficiency assessment of CWs. Highest total VOC removal was achieved during summer, being pronounced for benzene compared to MTBE. According to the experimental results and the calculations generated by the balancing model, degradation in the rhizosphere and plant uptake accounted for the main benzene removal processes, of 76% and 13% for the gravel bed CW and 83% and 11% for the root mat system. Volatilization flux of benzene and MTBE was low (<5%) for the gravel bed CW, while in the root mat system direct contact of aqueous and gaseous phases favored total MTBE volatilization (24%). With this applied approach, we present detailed contaminant mass balances that allow for conclusive quantitative estimation of contaminant elimination and distribution processes (e.g., total, surface, and phytovolatilization, plant uptake, rhizodegradation) in CWs under field conditions.

Lipopolysaccharide of Legionella pneumophila shed in a liquid culture as a nonvesicular fraction arrests phagosome maturation in amoeba and monocytic host cells.

After uptake by susceptible host cells, Legionella pneumophila displays the ability to arrest phagolysosome fusion. To elucidate the role of lipopolysaccharide (LPS) in this mechanism, we investigated its influence on Acanthamoeba castellanii, A/J mouse macrophages and human monocytes. For this, legionellae were cultured in broth to the replicative, noninfectious phase or to the infectious phase expressing virulence traits. Shed LPS-enriched outer membrane vesicles (OMV) and LPS species <300 kDa were obtained from L. pneumophila Corby strains possessing the virulence-associated LPS epitope recognized by monoclonal antibody (MAb) 3/1 and its mutant TF 3/1, which has lost this epitope due to a mutation in the lag-1 gene. The shed LPS components were attached by specific antibodies to latex beads and added to the host cells for phagocytosis. We demonstrated for the first time that evasion of lysosomal degradation of phagosomes for up to 5 h can also be set off by LPS that is not tied up in OMV. Moreover, our cell culture models showed that the influence of MAb 3/1-positive and -negative LPS was identical. Our data clearly substantiate that LPS is an independent factor for evading lysosomal degradation, which is independent of the bacterial expression of known virulence traits.