Nils Reiche

Aerated treatment pond technology with biofilm promoting mats for the bioremediation of benzene, MTBE and ammonium contaminated groundwater

A novel aerated treatment pond for enhanced biodegradation of groundwater contaminants was tested under field conditions. Coconut fibre and polypropylene textiles were used to encourage the development of contaminant-degrading biofilms. Groundwater contaminants targeted for removal were benzene, methyl tert-butyl ether (MTBE) and ammonium. Here, we present data from the first 14 months of operation and compare contaminant removal rates, volatilization losses, and biofilm development in one pond equipped with coconut fibre to another pond with polypropylene textiles. Oxygen concentrations were constantly monitored and adjusted by automated aeration modules. A natural transition from anoxic to oxic zones was simulated to minimize the volatilization rate of volatile organic contaminants. Both ponds showed constant reductions in benzene concentrations from 20 mg/L at the inflow to about 1 microg/L at the outflow of the system. A dynamic air chamber (DAC) measurement revealed that only 1% of benzene loss was due to volatilization, and suggests that benzene loss was predominantly due to aerobic mineralization. MTBE concentration was reduced from around 4 mg/L at the inflow to 3.4-2.4 mg/L in the system effluent during the first 8 months of operation, and was further reduced to 1.2 mg/L during the subsequent 6 months of operation. Ammonium concentrations decreased only slightly from around 59 mg/L at the inflow to 56 mg/L in the outflow, indicating no significant nitrification during the first 14 months of continuous operation. Confocal laser scanning microscopy (CLSM) demonstrated that microorganisms rapidly colonized both the coconut fibre and polypropylene textiles. Microbial community structure analysis performed using denaturing gradient gel electrophoresis (DGGE) revealed little similarity between patterns from water and textile samples. Coconut textiles were shown to be more effective than polypropylene fibre textiles for promoting the recruitment and development of MTBE-degrading biofilms. Biofilms of both textiles contained high numbers of benzene metabolizing bacteria suggesting that these materials provide favourable growth conditions for benzene degrading microorganisms.

Development and application of dynamic air chambers for measurement of volatilization fluxes of benzene and MTBE from constructed wetlands planted with common reed

Phytoremediation of industrially contaminated groundwater has been a proven technique for several decades. However, mass balances of contaminants are often focused in laboratory investigations. The evaluation of the transfer of volatile organic compounds (VOCs) under field conditions from the saturated and vadose soil zone into the atmosphere, directly or via plants, is rarely part of the research scope. This can provoke problems--particularly with regard to legal issues--if large-scale phytoremediation sites are situated near residential areas. In this study volatilization of VOCs was quantified in a horizontal-flow constructed wetland planted with reed grass. For this purpose, a specially designed air chamber was constructed, validated, and routine sampling campaigns were performed over the course of one year. Results indicate that the overall volatilization of the observed contaminants benzene and methyl tert-butyl ether (MTBE) depended on seasonal variations with the highest volatilization fluxes measured in summer, when the detected volatilization fluxes of 846+/-116 and 252+/-11 microg m(-2) h(-1) for MTBE and benzene, respectively, accounted for 2.4% and 5.6% of the respective overall contaminant mass loss in the planted wetland. Furthermore, chamber data give strong evidence for the increased volatilization of VOCs through vegetation by direct comparison of planted and unplanted wetlands.

Comparative evaluation of pilot scale horizontal subsurface-flow constructed wetlands and plant root mats for treating groundwater contaminated with benzene and MTBE

In order to evaluate technology options for the treatment of groundwater contaminated with benzene and MTBE in constructed wetlands (CWs), a scarcely applied plant root mat system and two horizontal subsurface-flow (HSSF) CWs were investigated. The inflow load of benzene and MTBE were 188-522 and 31-90 mg d(-1)m(-2), respectively. Higher removal efficiencies were obtained during summer in all systems. The benzene removal efficiencies were 0-33%, 24-100% and 22-100% in the unplanted HSSF-CW, planted HSSF-CW and the plant root mat, respectively; the MTBE removal efficiencies amounted to 0-33%, 16-93% and 8-93% in the unplanted HSSF-CW, planted HSSF-CW and the plant root mat, respectively. The volatilisation rates in the plant root mat amounted to 7.24 and 2.32 mg d(-1)m(-2) for benzene and MTBE, which is equivalent to 3.0% and 15.2% of the total removal. The volatilisation rates in the HSSF-CW reached 2.59 and 1.07 mg d(-1)m(-2), corresponding to 1.1% and 6.1% of the total removal of benzene and MTBE, respectively. The results indicate that plant root mats are an interesting option for the treatment of waters polluted with benzene and MTBE under moderate temperatures conditions.

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.

Microbial Toluene Removal in Hypoxic Model Constructed Wetlands Occurs Predominantly via the Ring Monooxygenation Pathway.

ABSTRACT In the present study, microbial toluene degradation in controlled constructed wetland model systems, planted fixed-bed reactors (PFRs), was queried with DNA-based methods in combination with stable isotope fractionation analysis and characterization of toluene-degrading microbial isolates. Two PFR replicates were operated with toluene as the sole external carbon and electron source for 2 years. The bulk redox conditions in these systems were hypoxic to anoxic. The autochthonous bacterial communities, as analyzed by Illumina sequencing of 16S rRNA gene amplicons, were mainly comprised of the families Xanthomonadaceae, Comamonadaceae, and Burkholderiaceae, plus Rhodospirillaceae in one of the PFR replicates. DNA microarray analyses of the catabolic potentials for aromatic compound degradation suggested the presence of the ring monooxygenation pathway in both systems, as well as the anaerobic toluene pathway in the PFR replicate with a high abundance of Rhodospirillaceae. The presence of catabolic genes encoding the ring monooxygenation pathway was verified by quantitative PCR analysis, utilizing the obtained toluene-degrading isolates as references. Stable isotope fractionation analysis showed low-level of carbon fractionation and only minimal hydrogen fractionation in both PFRs, which matches the fractionation signatures of monooxygenation and dioxygenation. In combination with the results of the DNA-based analyses, this suggests that toluene degradation occurs predominantly via ring monooxygenation in the PFRs.

Capability of headspace based sample preparation methods for the determination of methyl tert-butyl ether and benzene in reed (phragmites australis) from constructed wetlands

In order to investigate the fate of volatile pollutants such as methyl tert-butyl ether (MTBE) and benzene during the treatment of contaminated water using constructed wetlands, appropriate analytical methods for the analysis of wetland marsh plants, in our case common reed (Phragmites australis), are required. Different sampling procedures and different headspace (HS) based sample preparation techniques were examined to select and establish the most suited procedure for determining the target analytes in plant material. Static HS, dynamic HS and HS solid phase microextraction (SPME) in combination with GC-MS were optimized and evaluated regarding the extraction yields and their capability for quantitative analysis. Only dynamic HS analysis at 80 degrees C for 45min with trapping the analytes on Tenax TA/Chromosorb-106 desorption tubes and the subsequent thermodesorption GC-MS permits the quantitative analysis of MTBE and benzene in reed in a concentration range from 4ng up to 4mug per sample weight (approximately 1g). Static HS and HS SPME analyses were found to be less reliable due to the lack of suitable reference materials. Therefore, these methods do not permit the accurate quantification of pollutant content. Additionally, the HS SPME method is characterized by a restricted linear range of calibration curves. The optimized dynamic HS method was successfully applied for the quantitative analysis of MTBE and benzene within the plants. Their distribution within the plant depending on its height shows a different behavior due to differences in degradability of both substances. While a strong decrease of the concentration of benzene with increasing height of plant was found, the decrease of the concentration of MTBE was not as obvious as observed for benzene. Furthermore, the assessment of plant uptake during phytoremediation was demonstrated by analyzing complete plants for the constructed wetlands investigated.

Comparative study to evaluate three ground-based optical remote sensing techniques under field conditions by a gas tracer experiment

Today, ground-based optical remote sensing (ORS) has become an intensively used method for quantifying pollutant or greenhouse gas emissions from point or area sources, and for the validation of airborne or satellite remote sensing data. In this study, we present the results of a release experiment using acetylene (C2H2) as a tracer gas, where three ORS techniques were simultaneously tested for two main purposes: (1) the detection of emission sources and (2) the quantification of release rates. Therefore, passive and active open-path Fourier transform infrared spectroscopy (OP-FTIR) and open-path tunable diode laser absorption spectroscopy (TDLAS) were applied and evaluated. The concentration results of the active ORS methods are compared to those estimated by a Lagrangian stochastic atmospheric dispersion model. Our results reveal that passive OP-FTIR is a valuable tool for the rapid detection and imaging of emission sources and the spatial tracer gas distribution; while with active OP-FTIR and TDLAS, C2H2 concentrations in the sub-ppm range could be quantified that correlated well with the concentration data obtained by our modeling approach.

A solid-phase microextraction method for the in vivo sampling of MTBE in common reed (Phragmites australis)

Phytoscreening of phytoremediation-based plantings is discussed as a promising monitoring tool in literature. We developed and applied an analytical procedure for the in vivo sampling of methyl tert-butyl ether (MTBE) in the common reed (Phragmites australis) from a phytoremediation site highly polluted with MTBE. The approach uses solid-phase microextraction (SPME) with the SPME fibre directly introduced into the aerenchyma of the plant stem. For optimising the analytical procedure and estimating the capability of the proposed method, laboratory tests on the microcosm scale and field studies over one vegetation period were carried out. Furthermore, the results of in vivo SPME sampling were compared with those obtained with the traditional approach for analysing plants using dynamic headspace analysis. The MTBE signals detected within the plants were also correlated with the concentration in the water phase. The discussion of results showed the feasibility of the proposed method for a qualitative phytoscreening of volatile organic compounds present in wetland plants.

Ground-based Remote Sensing Using OP-FTIR Spectroscopy – A Feasibility Study for Application in Greenhouse Gas Control

Ground-based remote sensing by Open path Fourier-transform infrared (OP-FTIR) spectrometry provides data for the identification and quantification of emissions over wide surface areas. Large-scale OP-FTIR spectroscopy measurements are carried out associated with point-scale chamber-based soil CO2 flux measurement at a natural CO2 degassing area in the context of the hierarchical approach. The application of ground-based remote sensing using passive OP-FTIR spectroscopy represents a rapid and non-invasive assessment method for detecting variations in atmospheric concentrations of target gases and for the spatial identification of sources of increased gas concentrations. The presentation introduces results of a feasibility study investigating various scenarios such as urban regions, agricultural landscapes and natural CO2 degassing areas. Some examples of how to successfully deploy passive open path FTIR spectroscopy to identify anomalous greenhouse gas concentrations along greater optical pathways are presented.