Moderate Bioclogging Leading to Preferential Flow Paths in Biobarriers

Abstract

Permeable reactive barriers (PRBs) are an alternative technique for the biological in situ remediation of ground water contaminants. Nutrient supply via injection well galleries is supposed to support a high microbial activity in these barriers but can ultimately lead to changes in the hydraulic conductivity of the biobarrier due to the accumulation of biomass in the aquifer. This effect, called bioclogging, would limit the remediation efficiency of the biobarrier. To evaluate the effects bioclogging can have on the flow field of a PRB, flow cell experiments were carried out in the laboratory using glass beads as a porous medium. Two types of flow cells were used: a 20‐ × 1‐ × 1‐cm cell simulating a single injection well in a one‐dimensional flow field and a 20‐ × 10‐ × 1‐cm cell simulating an injection well gallery in a two‐dimensional flow field. A mineral medium was injected to promote microbial growth. Results of 9 d of continuous operation showed that conditions, which led to a moderate (50%) reduction of the hydraulic conductivity of the one‐dimensional cell, led to a preferential flow pattern within the simulated barrier in the two‐dimensional flow field (visualized by a tracer dye). The bioclogging leading to this preferential flow pattern did not change the hydraulic conductivity of the biobarrier as a whole but resulted in a reduced residence time of water within barrier. The biomass distribution measured after 9 d was consistent with the observed clogging effects showing step spatial gradients between clogged and unclogged regions.

Metabolic uncoupling of Shewanella oneidensis MR‐1, under the influence of excess substrate and 3, 3′, 4′, 5‐tetrachlorosalicylanilide (TCS)

“…This is accompanied by generation of biomass, an excess of which could increase the operational cost and reduce the efficiency of engineered systems, such as municipal wastewater treatment (Liu and Tay, 2001;Liu, 2003;Mayhew and Stephenson, 1997;Wei et al, 2003) and could lead to bioclogging in in situ bioremediation systems. In such subsurface systems, the biomass can plug the soil pores, causing a reduction in the hydraulic conductivity of the system and an inability for the substrate to be transported effectively from injection wells (McCarty et al, 1998;Seki et al, 2006;Taylor and Jaffe, 1990). In extreme cases, this lack of control over microbial growth leads to a shift in the dominant microbial population (due to a higher consumption rate of the preferred electron acceptor) and possible failure of the bioremediation scheme (Anderson et al, 2003).…”

On-site and in situ remediation technologies applicable to petroleum hydrocarbon contaminated sites in the Antarctic and Arctic

“…The development of permeable bioreactive barriers can have positive implications for the longevity of petroleum hydrocarbon adsorption material within a PRB; however, the promotion of biomass has the potential to reduce media permeability (Seki et al 2006). The permeability of PRBs can be reduced by biomass accumulation or by microbial gas production, either of which can clog the reactive zone of a PRB (Seki et al 2006;Yeh et al 2010).…”

“…The permeability of PRBs can be reduced by biomass accumulation or by microbial gas production, either of which can clog the reactive zone of a PRB (Seki et al 2006;Yeh et al 2010). Maintaining optimal biomass density is critical for PRBs, as the accumulation of a sufficient amount of biomass is necessary for bioremediation.…”

Hydraulic performance of a permeable reactive barrier at Casey Station, Antarctica

“…Of particular importance is ensuring; all flow is intercepted, that is flow is funneled towards the reactive gate and no short circuiting of the gate occurs. This must hold even as precipitates are formed (Parbs et al, 2007), gas is evolved (Henderson and Demond, 2011), hydrocarbons captured (Mumford et al, 2013) or biofilms grown (Seki et al, 2006 A number of approaches can be used to evaluate the hydraulic performance of PRB installations including hydraulic gradient measurements combined with hydraulic conductivity data (Gavaskar et al, 2002), in situ flow measurements (Gavaskar et al, 2002), tracer tests and geochemical changes measured upand down-gradient of the PRB coupled with mass balance calculations (Wilkin et al, 2003). However, on occasion these methods vary in their conclusions or have limits on their accuracy.…”