Peter Kuschk

Monitoring and assessing processes of organic chemicals removal in constructed wetlands

Physical, chemical and biological processes interact and work in concert during attenuation of organic chemicals in wetland systems. This review summarizes the recent progress made towards understanding how the various mechanisms attributed to organic chemicals removal interact to form a functioning wetland. We also discuss the main degradation pathways for different groups of contaminants and examine some of the key characteristics of constructed wetlands that control the removal of organic chemicals. Furthermore, we address possible comprehensive approaches and recent techniques to follow up in situ processes within the system, especially those involved in the biodegradation processes.

Development of constructed wetlands in performance intensifications for wastewater treatment: a nitrogen and organic matter targeted review.

The knowledge on the performance enhancement of nitrogen and organic matter in the expanded constructed wetlands (CWs) with various new designs, configurations, and technology combinations are still not sufficiently summarized. A comprehensive review is accordingly necessary for better understanding of this state-of-the-art-technology for optimum design and new ideas. Considering that the prevailing redox conditions in CWs have a strong effect on removal mechanisms and highly depend on wetland designs and operations, this paper reviews different operation strategies (recirculation, aeration, tidal operation, flow direction reciprocation, and earthworm integration), innovative designs, and configurations (circular-flow corridor wetlands, towery hybrid CWs, baffled subsurface CWs) for the intensifications of the performance. Some new combinations of CWs with technologies in other field for wastewater treatment, such as microbial fuel cell, are also discussed. To improve biofilm development, the selection and utilization of some specific substrates are summarized. Finally, we review the advances in electron donor supply to enhance low C/N wastewater treatment and in thermal insulation against low temperature to maintain CWs running in the cold areas. This paper aims to provide and inspire some new ideas in the development of intensified CWs mainly for the removal of nitrogen and organic matter. The stability and sustainability of these technologies should be further qualified.

Potential roles of anaerobic ammonium and methane oxidation in the nitrogen cycle of wetland ecosystems

Anaerobic ammonium oxidation (anammox) and anaerobic methane oxidation (ANME coupled to denitrification) with nitrite as electron acceptor are two of the most recent discoveries in the microbial nitrogen cycle. Currently the anammox process has been relatively well investigated in a number of natural and man-made ecosystems, while ANME coupled to denitrification has only been observed in a limited number of freshwater ecosystems. The ubiquitous presence of anammox bacteria in marine ecosystems has changed our knowledge of the global nitrogen cycle. Up to 50% of N2 production in marine sediments and oxygen-depleted zones may be attributed to anammox bacteria. However, there are only few indications of anammox in natural and constructed freshwater wetlands. In this paper, the potential role of anammox and denitrifying methanotrophic bacteria in natural and artificial wetlands is discussed in relation to global warming. The focus of the review is to explore and analyze if suitable environmental conditions exist for anammox and denitrifying methanotrophic bacteria in nitrogen-rich freshwater wetlands.

Plant--rhizosphere-microflora association during phytoremediation of PAH-contaminated soil.

The capability of plants to promote the microbial degradation of pollutants in rhizosphere soil is a principal mechanism of phytoremediation of PAH-contaminated soil. The formation of a specific rhizosphere microbocenosis with a high degradative potential toward contaminants is largely determined by plant species. The comparative PAH-degradation in unplanted soil and in soil planted with reed (Phragmites australis) and alfalfa (Medicago sativa) was studied in pot experiments during 2 years. Both alfalfa and reed successfully remediated contaminated soil by degrading 74.5 and 68.7% of PAHs, respectively. The study of the rhizosphere, rhizoplane, and unplanted-soil microflora in experimental pots showed that alfalfa stimulated the rhizosphere microflora of PAH-contaminated soil more effectively than did reed. Alfalfa clearly enhanced both the total number of microorganisms (1.3 times, according to fluorescence microscopy data) and the rate of the PAH-degrading population (almost seven times, according to plate counting). The degradative potential of its rhizosphere microflora toward PAHs was higher than the degradative activity of the reed rhizosphere. This study provides relevant information for the successful application of alfalfa to phytoremediate PAH-contaminated soil.

Model experiments on the microbial removal of chromium from contaminated groundwater.

A bacterial consortium with representatives of sulfate-reducing and denitrifying bacteria was selectively enriched. Model experiments under microaerobic conditions showed that it precipitated chromium from Cr (VI)-containing waters (area of a former electroplating factory, Leipzig, Germany) by two different mechanisms: by sulfate reduction and precipitation as sulfide, and by some direct reduction. Sulfate reduction needed fatty acids as organic substrates and resulted at the first stage in no sulfide accumulation. In the absence of the fatty acids but with straw as organic substrate, the direct reduction of chromium was observed without sulfate reduction. In this case Cr (VI)-reduction rate correlated with that of the denitrification.

Oxygen Release by Roots of Typha latifolia and Juncus effusus in Laboratory Hydroponic Systems

Laboratory-scale investigations using individual T.latifolia and J. effusus plants in hydroponic systems were carried out to evaluate the potentials and differences in the species regarding the release of oxygen into their rhizospheres. Their oxygen release intensities were found to vary between the species and also to depend on the redox state of the rhizosphere. The highest release rates with mean values of 1.1 mg/h plant for T.latifolia and 0.5 mg/h plant for J.effusus were estimated at Eh - - 200 mV for both species. The amounts of oxygen released were sufficient to be of biotechnological relevance for oxidative processes in constructed wetlands. The plants even released oxygen under oxidized rhizospheric conditions and for individual plants, an intensification of the oxygen release was estimated, forming further local release maxima at Eh = 250-400 mV with about 0.2 mg/h plant. The total size of the root system does not significantly affect the intensity of oxygen release; instead, the oxygen release state was governed by the size of the above-ground biomass. The intensification of illumination causes an increase in the oxygen release rates, which is pronounced for T.latifolia but small for J.effusus. Further investigations involving other wetland species and using laboratory-scale, pilot-scale and full-scale wetland systems to evaluate oxygen release are of biotechnological interest.

Abilities of Helophyte Species to Release Oxygen into Rhizospheres with Varying Redox Conditions in Laboratory-Scale Hydroponic Systems

ABSTRACT Plantlets of the wetland species cattail (Typha latifolia), reed (Phragmites australis), rush (Juncus effusus), and yellow flag (Iris pseudacorus) grown from seedlings or cuttings were investigated in laboratory-scale hydroponic systems in order to determine the intensity of oxygen release into the rhizosphere under various redox conditions. The initial redox conditions of the rhizosphere were modified by adding different amounts of titanium (III) citrate. All the plantlets investigated released oxygen into the rhizosphere (0.01 mg/h * plant to 1.41 mg/h * plant), depending on the actual conditions of each experiment. The intensity of release was found to be controlled by the external oxygen demand in the rhizosphere for the whole range of conditions from extremely reduced to oxidized. The capacities of the plantlets to release oxygen were found to be species-specific under reduced conditions in the rhizosphere (–400 mV to +200 mV). Under conditions of higher redox potential (>+200 mV) the oxygen release depends on the physiological status of the individual plant. Oxygen release rates are highest in the range–250 mV < Eh < −150 mV. For the species investigated, the highest rates were observed for Typha latifolia (1.41 mg/h * plant) followed by Phragmites australis (1 mg/h * plant), Juncus effusus (0.69 mg/h * plant), and Iris pseudacorus (0.34 mg/h * plant). In general, the plantlets released oxygen with different rates into a nonbuffered rhizosphere until highly oxidized conditions in the root-near environment prevailed. The presented oxygen-releasing behavior is a process dominating natural conditions within the rhizosphere and is relevant to wetland systems and for conceptual approaches in phytoremediation.

Soils as source and sink of phosphine

Abstract The evolution of free phosphine from soil samples collected from seven different areas in Germany was observed in laboratory experiments. Phosphine emissions increased after additions of manure, glucose, formate, pyrogallol and sulphide, revealing a potential influence of microbial activity on the liberation of phosphine. However, the concentrations decreased as time progressed. Soil samples exposed to phosphine removed the gas according to an exponential relationship. When Fe(III) was added to soil samples, phosphine removal was accelerated. The release of phosphine from soils to the atmosphere was concluded to be dependent on a balance of natural generation and depletion processes. At every time “matrix-bound” phosphine, which constitutes a trace of this balance, can be liberated by acid digestion of the soils.

Phosphine by bio-corrosion of phosphide-rich iron

Phosphine is a toxic agent and part of the phosphorus cycle. A hitherto unknown formation mechanism for phosphine in the environment was investigated. When iron samples containing iron phosphide were incubated in corrosive aquatic media affected by microbial metabolites, phosphine was liberated and measured by gas chromatography. Iron liberates phosphine especially in anoxic aquatic media under the influence of sulfide and an acidic pH. A phosphine-forming mechanism is suggested: Phosphate, an impurity of iron containing minerals, is reduced abioticly to iron phosphide. When iron is exposed to the environment (e.g. as outdoor equipment, scrap, contamination in iron milled food or as iron meteorites) and corrodes, the iron phosphide present in the iron is suspended in the medium and can hydrolyze to phosphine. Phosphine can accumulate to measurable quantities in anoxic microbial media, accelerating corrosion and preserving the phosphine formed from oxidation.

Rhizosphere microflora of plants used for the phytoremediation of bitumen-contaminated soil.

The microbial communities and their degradative potential in rhizospheres of alfalfa (Medicago sativa) and reed (Phragmites australis) and in unplanted soil in response to bitumen contamination of soil were studied in pot experiments. According to the results of fluorescence microscopy, over a period of 27 months, bitumen contamination of soil reduced the total number of microorganisms more significantly (by 75%) in unplanted than in rhizosphere soil (by 42% and 7% for reed and alfalfa, respectively) and had various effects on some important physiological groups of microorganisms such as actinomycetes as well as nitrogen-fixing, nitrifying, denitrifying, ammonifying, phosphate-solubilizing, sulphur-oxidizing, cellulolytic and hydrocarbon-degrading microorganisms. The changes in the physiological structure of the microbial community under bitumen contamination were found to hinge on not merely the presence of plants but also their type. It was noted that the rhizosphere microflora of alfalfa was less inhibited by hydrocarbon pollution and had a higher degradative potential than the rhizosphere microflora of reed.