Groundwater remediation | EPFL Graph Search

Groundwater remediation is the process that is used to treat polluted groundwater by removing the pollutants or converting them into harmless products. Groundwater is water present below the ground surface that saturates the pore space in the subsurface. Globally, between 25 per cent and 40 per cent of the world's drinking water is drawn from boreholes and dug wells. Groundwater is also used by farmers to irrigate crops and by industries to produce everyday goods. Most groundwater is clean, but groundwater can become polluted, or contaminated as a result of human activities or as a result of natural conditions. The many and diverse activities of humans produce innumerable waste materials and by-products. Historically, the disposal of such waste have not been subject to many regulatory controls. Consequently, waste materials have often been disposed of or stored on land surfaces where they percolate into the underlying groundwater. As a result, the contaminated groundwater is unsuitabl

Study of the microbial communities of core and water samples in a chloroethenes contaminated aquifer

Guillaume Laulan

Widely used in industrial activities, chloroethenes have become common groundwater contaminants. Dehalorespiration is an anaerobic bacterial respiration coupling their sequential degradation to energy production. The interactions between the dehalorespiring bacteria and the other guilds and environmental variables are presumed to influence the dehalorespiration efficiency. Here, water and core samples were extracted from the PCE-contaminated site of Lyss (BE, Switzerland). Bacterial DNA was extracted and the 16S rRNA gene amplified by PCR. Terminal restriction fragment length polymorphism (T-RFLP) was used to assess the diversity of the bacterial communities. Core and groundwater environmental variables were analyzed as well. The T-RFLP profiles and the environmental data obtained were processed using statistical multivariate analysis. Within a period of two months, the bacterial communities remained relatively specific to their respective sampling origins. Communities from the oxic layer shared a similar set of bacterial species whereas piezometers from the anoxic layer had a specific one. The T-RFLP profiles obtained from single depth and multi-level piezometers were clearly distinct, probably due to differences in the pumping flow rates and their associated transport regimes, which can have an impact on i) the sediments extracted from the aquifer, ii) the hydraulic zone reached and iii) a potential selective bacterial adsorption onto the pumping tube wall. Environmental factors related to the groundwater redox state appeared as the major variables influencing the bacterial populations. Bacterial communities from core samples clustered into two distinct sets: i) samples from the strongly reductive silt layer, and ii) samples from the coarser and less reductive layer. Grain size distribution and redox state both had a major influence on the bacterial communities of core samples. Finally, it was shown that microbial populations extracted from groundwater differed from the ones extracted from core material, and thus were not representative of the overall aquifer microbial diversity.

2009

Influence of pH on dehalorespiring consortia & first steps in the development of a methodology for acid neutralization in enhanced in situ bioremediation

Nicole Munz

Enhanced in situ bioremediation of chlorinated solvents is, especially in source zone remediation, often limited through the accompanied high acidification of groundwater. This acid built-up originating from the dechlorination itself and fermentation products, such as organic acids, presents a draw-back in the efficiency of dehalorespiring bacteria. It is therefore indispensable to develop and implement appropriate buffering strategies to ensure a constant transformation of toxic chloroethenes to the final non-toxic product ethene. In this study pH tolerance of different dehalorespiring bacteria was tested. The limiting acidic pH varies significantly among the consortia. The consortium SL23b4 (PCE to ethene) grows at all the examined pH (pH 5 to pH 7.5) with a pH optimum between 6 and 7 (depending on the dechlorination step), whereas Maroc 6b (PCE to ethene) was only found to grow at incubation pH of 7, and very slowly at pH 6.5. The consortium 2SO (cis-DCE to ethene) seems to be inhibited at acidic pH (no growth at pH 5 and 5.5) having a pH optimum above neutral pH. In most cases incomplete dechlorination was observed in cultures growing at acidic pH or below the pH optima, accumulating toxic intermediate dechlorination products as a consequence. Additionally, high rates of dechlorination were always accompanied by pH drops up to 1.2 pH units, giving evidence of high acid production. pH had also influence on the community composition. In the consortium SL23b4 a shift from a Dehalococcoides- (pH 6-7.5) to a Sulfurospirillum spp.- (pH5 -5.5) dominated community was observed. Consortium Maroc 6b showed significantly different community compositions due to a pH change of only 0.5 pH units. Dehalococcoides spp. and Dehalobacter spp. were dominating at pH 7 and pH 6.5, respectively. Consortium 2SO is dominated by Dehalococcoides spp. at all pH, although at pH 7 a much higher diversity seems to prevail, with the threefold number of OTUs. Tests on the tolerance of the dehalorespiring consortia for elevated PCE concentration showed similar patterns for the different dechlorination steps, as for pH cultures, and confirmed a generally higher sensitivity towards PCE and pH changes for the last steps of dechlorination. Conclusively, Dehalococcoides spp., the only known genera able to perform complete dechlorination, seem to be highly sensitive to pH and PCE changes. Further, abiotic experiments on silicate mineral dissolution, using forsteritic olivine, were performed to simulate the buffer capacity of the minerals for the acid production during microbial reductive dechlorination. In these experiments, the buffer capacity was insufficient to counterbalance the constant acid titration rate, resulting in a final pH between 3 and 4 (initial pH of 7). The formation of precipitates, such as iron oxide, and the re-precipitation of magnesium were observed in some cases, showing a decrease in magnesium concentrations.

2010

Impact Assessment of Pumping Parameters on Groundwater Bacterial Communities

Christof Holliger, Guillaume Laulan, Pierre Rossi, Noam Shani

Groundwater microbial community samples are traditionally collected using pumping techniques optimized for groundwater chemistry assessment, although the impact of groundwater pumping parameters on apparent bacterial community structures (BCSs) is not really known. We therefore studied the impact of pumping lift, flow regime, and tubing material on BCS, which were analyzed by terminal-restriction fragment length polymorphism (T-RFLP). Ruzicka dissimilarity coefficients were calculated between T-RFLP profiles to assess disparities between BCS. Variations in pumping lift, flow regime, and tubing material did not affect the apparent BCS in experiments using a homogenous water system under laboratory conditions showing that the conditions within the tube had no detectable effect on BCS. However, pumping groundwater from aquifer monitoring wells at different flow rates in the field revealed a significant impact on the apparent BCS. Water samples collected from fine sediment were the most affected by the pumping flow rate.

Wiley-Blackwell2013