Citrate Addition Increased Phosphorus Bioavailability and Enhanced Gasoline Bioremediation

Abstract

Phosphorus (P) bioavailability often limits gasoline biodegradation in calcareous cold-region soils. One possible method to increase P bioavailability in such soils is the addition of citrate. Citrate addition at the field scale may increase hydrocarbon degradation by: (i) enhancing inorganic and organic P dissolution and desorption, (ii) increasing hydrocarbon bioavailability, and/or (iii) stimulating microbial activity. Alternatively, citrate addition may inhibit activity due to competitive effects on carbon metabolism. Using a field-scale in situ biostimulation study, we evaluated if citrate could stimulate gasoline degradation and what the dominant mechanism of this stimulation will be. Two large bore injectors were constructed at a site contaminated with gasoline, and a biostimulation solution of 11 mM MgSO, 1 mM HPO, and 0.08 mM HNO at pH 6.5 in municipal potable water was injected at ∼5000 L d for about 4 mo. Following this, 10 mM citric acid was incorporated into the existing biostimulation solution and the site continued to be stimulated for 8 mo. After citrate addition, the bioavailable P fraction in groundwater and soil increased. Iron(II) groundwater concentrations increased and corresponded to decreases in benzene, toluene, ethylbenzene, xylenes (BTEX) in groundwater, as well as a decrease in F1 in the soil saturated zone. Overall, citrate addition increased P bioavailability and may stimulate anaerobic microbial activity, resulting in accelerated anaerobic gasoline bioremediation in cold-region calcareous soils.

Soil Buffering Capacity Can Be Used To Optimize Biostimulation of Psychrotrophic Hydrocarbon Remediation

“…One solution is the use of ligands , that chelate Ca and Fe and prevent phosphorus precipitation. Such chelators can help sustain bioremediation . However, biostimulatory solutions also slowly dissolve soil carbonates.…”

“…Such chelators can help sustain bioremediation. 15 However, biostimulatory solutions also slowly dissolve soil carbonates. the precipitation of Ca/Mg phosphate minerals, which are less bioaccessible to microbes than adsorbed or dissolved P. If we assume that phosphorus must remain bioavailable for hydrocarbon bioremediation to occur, 15,16 then approaches that modify biostimulatory solutions to minimize phosphate precipitation in soils of differing buffering capacities should outperform standard, one-size-fits-all approaches toward microbial biostimulation.…”

“…15 However, biostimulatory solutions also slowly dissolve soil carbonates. the precipitation of Ca/Mg phosphate minerals, which are less bioaccessible to microbes than adsorbed or dissolved P. If we assume that phosphorus must remain bioavailable for hydrocarbon bioremediation to occur, 15,16 then approaches that modify biostimulatory solutions to minimize phosphate precipitation in soils of differing buffering capacities should outperform standard, one-size-fits-all approaches toward microbial biostimulation. A wide range of bacteria anaerobically degrade hydrocarbons, 17 and thus, some biostimulatory approaches add nutrients to maintain a C/N ratio of approximately 10 to optimize the metabolic activity.…”

A sustainable colloidal material with sorption and nutrient‐supply capabilities for in situ groundwater bioremediation

“…At residual saturation (middle to late stages of LNAPL release), dissolution followed by microbial degradation of LNAPL constituents are the main processes that deplete LNAPL (CL:AIRE, 2014; Sale et al, 2018). Microbial degradation is enhanced by providing nutrients and electron acceptors; in some cases, the microbial community is augmented with desired species (Bosma et al, 1997;Chen et al, 2017;Ławniczak et al, 2020). Nevertheless, depletion of residual LNAPL proceeds at a slow rate due to mass transfer limitations of LNAPL constituents (slow rates of dissolution and entrapment in aquifer matrix) and the low availability of P (Bosma et al, 1997;CL:AIRE, 2014;Sale et al, 2018;Siciliano et al, 2016).…”

Assessing Space, Time, and Remediation Contribution to Soil Pollutant Variation near the Detection Limit Using Hurdle Models to Account for a Large Proportion of Nondetectable Results

“…Here, we used benzene as a case study to develop a statistical approach to assess treatment effects on pollutants near DLs and to obtain the influence of spatial parameters by corresponding coefficients. In our case, nutrient and electron acceptors (biostimulatory solution) were supplied to remediate the contaminated sites. ,− All the pollution occurred in the subsurface and the soils of the region are calcareous, thus limiting nutrients for the anaerobic microorganisms likely associated with degrading pollutants. Our objectives were to (1) compare the moment (mean and variance) of censored data based on the gamma distribution before and after remediation, (2) incorporate the use of a hurdle model to fit environmental censored data, and (3) calculate the biostimulation and spatial effect on benzene variation by using the hurdle model.…”