Microbial Community Changes in a Chlorinated Solvents Polluted Aquifer Over the Field Scale Treatment With Poly-3-Hydroxybutyrate as Amendment.

This study investigated the organohalide-respiring bacteria (OHRB) and the supporting microbial populations operating in a pilot scale plant employing poly-3-hydroxybutyrate (PHB), a biodegradable polymer produced by bacteria from waste streams, for the in situ bioremediation of groundwater contaminated by chlorinated solvents. The bioremediation was performed in ground treatment units, including PHB reactors as slow release source of electron donors, where groundwater extracted from the wells flows through before the re-infiltration to the low permeability zones of the aquifer. The coupling of the biological treatment with groundwater recirculation allowed to drastically reducing the contamination level and the remediation time by efficiently stimulating the growth of autochthonous OHRB and enhancing the mobilization of the pollutants. Quantitative PCR performed along the external treatment unit showed that the PHB reactor may efficiently act as an external incubator to growing Dehalococcoides mccartyi, known to be capable of fully converting chlorinated ethenes to innocuous end-products. The slow release source of electron donors for the bioremediation process allowed the establishment of a stable population of D. mccartyi, mainly carrying bvcA and vcrA genes which are implicated in the metabolic conversion of vinyl chloride to harmless ethene. Next generation sequencing was performed to analyze the phylogenetic diversity of the groundwater microbiome before and after the bioremediation treatment and allowed the identification of the microorganisms working closely with organohalide-respiring bacteria.

Metabolic synergies in the biotransformation of organic and metallic toxic compounds by a saprotrophic soil fungus.

The saprotrophic fungus Penicillium griseofulvum was chosen as model organism to study responses to a mixture of hexachlorocyclohexane (HCH) isomers (α-HCH, ß-HCH, γ-HCH, δ-HCH) and potentially toxic metals (vanadium, lead) in solid and liquid media. The P. griseofulvum FBL 500 strain was isolated from polluted soil containing high concentrations of HCH isomers and potentially toxic elements (Pb, V). Experiments were performed in order to analyse the tolerance/resistance of this fungus to xenobiotics and to shed further light on fungal potential in inorganic and organic biotransformations. The aim was to examine the ecological and bioremedial potential of this fungus verifying the presence of mechanisms that allow it to transform HCH isomers and metals under different extreme test conditions. To our knowledge, this work is the first to provide evidence on the biotransformation of HCH mixtures, in combination with toxic metals, by a saprotrophic non-white-rot fungus and on the metabolic synergies involved.

Polyhydroxyalkanoate as a slow-release carbon source for in situ bioremediation of contaminated aquifers: From laboratory investigation to pilot-scale testing in the field.

A pilot-scale study aiming to evaluate the potential use of poly-3-hydroxy-butyrate (PHB) as an electron donor source for in situ bioremediation of chlorinated hydrocarbons in groundwater was conducted. Compared with commercially available electron donors, PHB offers a restricted fermentation pathway (i.e., through acetic acid and molecular hydrogen) by avoiding the formation of any residual carbon that could potentially spoil groundwater quality. The pilot study was carried out at an industrial site in Italy, heavily contaminated by different chlorinated aliphatic hydrocarbons (CAHs). Prior to field testing, PHB was experimentally verified as a suitable electron donor for biological reductive dechlorination processes at the investigated site by microcosm studies carried out on site aquifer material and measuring the quantitative transformation of detected CAHs to ethene. Owing to the complex geological characteristics of the aquifer, the use of a groundwater circulation well (GCW) was identified as a potential strategy to enable effective delivery and distribution of electron donors in less permeable layers and to mobilise contaminants. A 3-screened, 30-m-deep GCW coupled with an external treatment unit was installed at the site. The effect of PHB fermentation products on the in situ reductive dechlorination processes were evaluated by quantitative real-time polymerase chain reaction (qPCR). The results from the first 4 months of operation clearly demonstrated that the PHB fermentation products were effectively delivered to the aquifer and positively influenced the biological dechlorination activity. Indeed, an increased abundance of Dehalococcoides mccartyi (up to 6.6 fold) and reduced CAH concentrations at the installed monitoring wells were observed.

Biotransformation of ß-hexachlorocyclohexane by the saprotrophic soil fungus Penicillium griseofulvum.

ß-Hexachlorocyclohexane (ß-HCH) is a persistent organic pollutant (POP) of global concern with potentially toxic effects on humans and ecosystems. Fungal tolerance and biotransformation of toxic substances hold considerable promise in environmental remediation technologies as many fungi can tolerate extreme environmental conditions and possess efficient extracellular degradative enzymes with relatively non-specific activities. In this research, we have investigated the potential of a saprotrophic soil fungus, Penicillium griseofulvum Dierckx, isolated from soils with high concentrations of isomers of hexachlorocyclohexane, to biotransform ß-HCH, the most recalcitrant isomer to microbial activity. The growth kinetics of the fungus were characterized after growth in stirred liquid Czapek-Dox medium. It was found that P. griseofulvum was able to grow in the presence of 1 mg L(-1) ß-HCH and in stressful nutritional conditions at different concentrations of sucrose in the medium (0 and 5 g L(-1)). The effects of ß-HCH and the toluene, used as a solvent for ß-HCH addition, on P. griseofulvum were investigated by means of a Phenotype MicroArray™ technique, which suggested the activation of certain metabolic pathways as a response to oxidative stress due to the presence of the xenobiotics. Gas chromatographic analysis of ß-HCH concentration confirmed biodegradation of the isomer with a minimum value of ß-HCH residual concentration of 18.6%. The formation of benzoic acid derivatives as dead-end products of ß-HCH biotransformation was observed and this could arise from a possible biodegradation pathway for ß-HCH with important connections to fungal secondary metabolism.

Polyhydroxyalkanoate (PHB) as a slow-release electron donor for advanced in situ bioremediation of chlorinated solvent-contaminated aquifers.

During the last two decades permeable reactive barriers (PRBs) established as robust alternatives to traditional pump & treat approaches for groundwater remediation. Zero-valent iron (ZVI) is currently the most frequently employed reactive media, especially for treating plumes polluted by chlorinated hydrocarbons. However PRB-ZVI technology is affected by some problems such as the long-term performance decrease, loss of porosity and no applicability to some important compounds, such as 1,2-dichloroetane (1,2-DCA). In this study we wanted to investigate whether the coupling of ZVI with a long-lasting slow-release substrate (i.e. poly-hydroxybutyrate, PHB) could be a strategy to enhance the degradation performance of ZVI barriers towards chlorinated ethanes especially stimulating biological reductive dechlorination downgradient the PRB. Results here presented clearly demonstrate the feasibility of the proposed approach and the possibility that a biodegradable polymer, usually produced for different commercial sectors, could be advantageously used in the groundwater remediation market.