The biogeochemical processes controlling the reductive transformation of contaminants in an anaerobic aquifer were inferred from the relative reactivity patterns of redox-sensitive probe compounds. The fate of five nitroaromatic compounds (NACs) was monitored under different redox conditions in a landfill leachate plume of a sandy aquifer. Results of field experiments (continuous injection and in situ microcosms) were compared to the findings of laboratory batch and column experiments (using aquifer matrix and model systems for sulfate- and iron-reducing conditions). NACs were transformed within 2−70 days in the leachate plume as well as in microbially active and in microbially deactivated experiments. Generally, aromatic amines were the predominant reduction products, and these compounds were stable within the time frame and under the conditions of our experiments. Despite the presence of various potential reductants (e.g., H2S/HS-, Fe(II)aq, reduced organic matter, microorganisms), the patterns of relative reactivity of the probe compounds indicated that ferrous iron associated with iron(III) (hydr)oxide surfaces was the dominant reductant throughout the anaerobic region of the plume. Our results suggest that Fe(II) associated with ferric iron minerals is a highly reactive reductant in anaerobic aquifers, which may also determine the fate of other classes of reducible contaminants such as halogenated solvents, azo compounds, sulfoxides, chromate, or arsenate.
A lab-scale biofilter was run continuously for 1½ years for combined denitrification and phosphorus removal. lternation between anaerobic and anoxic (nitrate) conditions was used to obtain an enriched culture of denitrifying, phosphate accumulating organisms. Batch experiments were performed to test the importance of diffusion and zonation in the biofilm. Half- and zero-order anaerobic phosphate release and anoxic phosphate uptake rates were verified, which was taken as an indication of a zonated biofilm. To investigate the practical applicability of the process, the development of a computer model is necessary due to the high complexity of the process. AQUASIM is suitable for this purpose. The model can provide insight into what goes on inside the biofilm and act as a tool when predicting required tank sizes, optimal phase lengths and biofilm thickness etc. for a large-scale system. For control of the process, on-line measurements and computer control of the system are essential.
The degradation potential of the herbicides 2,4-D, 2,4,5-T, atrazine, dichlobenil, DNOC, bentazone, DCP (dichloroprop), IPU (isoproturon), MCPA and MCPP (mecoprop) and the degradation product from dichlobenil 2,6-dichlorobenzamide (BAM) were investigated in laboratory incubations with sediment and groundwater from eight Danish anaerobic and aerobic aquifers.
A continuous, natural‐gradient field injection experiment, involving 18 xenobiotic compounds and bromide as tracers, was performed in the anaerobic region of a leachate plume downgradient from the Grindsted Landfill, Denmark. The injection lasted for 195 days, and within this period a continuous cloud was established. Over a period of 924 days the cloud movement was monitored in approximately 70 discrete sampling points in the central part of the cloud, and the spatial distribution was described by seven cloud snapshots involving 400–700 sampling points. The bromide cloud movement closely followed the varying flow direction predicted by the water table measurements. Moment analysis showed decreasing tracer flow velocities and reduced capture of bromide mass with time, which may be explained by varying flow conditions (direction, hydraulic gradient) and the heterogeneous geological conditions in the sandy aquifer. Naphthalene, having the highest log K ow value, was the most retarded compound, with a retardation of less than 10%. Therefore sorption was not considered to be a significant attenuation process for any of the compounds studied. Transformation under iron‐reducing conditions was observed for toluene, o ‐xylene, TeCM, 1,1,1‐TCA, PCE, and TCE, while transformation of benzene and napthalene was not detected in the aquifer within the time frame of this study. First‐order transformation rates were in the range of 0.028–0.039 d −1 and 0.0014–0.0028 d −1 for the aromatic compounds toluene and o ‐xylene, respectively. The rates for the chlorinated aliphatic compounds, tetrachloromethane, 1,1,1‐ trichloroethane, tetrachloroethylene, and trichloroethylene, were >0.7 d −1 , 0.0044–0.0054 d −1 , 0.0012–0.0038 d −1 , and 0.0003–0.001 d −1 , respectively. Long lag periods and slow transformation rates were observed for some of the compounds, suggesting that lack of transformation reported in the literature may be attributable to short experimental periods in those studies.
ABSTRACT A method for identifying and quantifying bitumen particles, generated from the wear of roadway asphalts, in aerosol and soil samples has been developed. Bitumen is found to be the only contributor to airborne particles containing organic molecules with molecular weights larger than 2000 g pr. mol. These are separated and identified using High Performance Gel Permeation Chromatography (HP-GPC) with fluorescence detection. As an additional detection method Infra Red spectrometry (IR) is employed for selected samples, The methods have been used on aerosol, soil and other samples.
