Bioremediation of PAHs-contaminated site in a full-scale biopiling system with immobilized enzymes: Removal efficiency and microbial communities

Bioremediation of PAHs-contaminated soil by immobilized enzymes is a promising technology. Nevertheless, the practical implementation of highly efficient enzymatic remediation remains confined to laboratory settings, with limited experience in full-scale applications. In this study, the extracellular enzymes from white rot fungi are fully applied to treat sites contaminated with PAHs by combining a new hydrogel microenvironment and a biopiling system. The full-scale project was conducted on silty loam soil contaminated with PAHs. In line with China's guidelines for construction land, 7 out of the 12 PAHs identified are considered to be a threat to the soil quality of construction sites, with benzo[a]pyrene levels reaching 1.50 mg kg-1, surpassing the acceptable limit of 0.55 mg kg-1 for the first type of land. After 7 days of remediation, the benzo[a]pyrene level decreased from 1.50 mg kg-1 to 0.51 mg kg-1, reaching the remediation standard of Class I screening values, with a removal rate of 66%. Microbiomes were utilized to assess the microbial biodiversity and structure analyses for PAHs biodegradation. The remediation enhanced the abundance of dominant bacterium (Marinobacter, Pseudomonas, and Truepera) and fugin (Thielavia, Neocosmospora, and Scedosporium). The research offers further insights into the exploration of soil remediation on the full-scale of the immobilized enzyme and biopiling technology.

Sulfate-reducing bacteria unearthed: ecological functions of the diverse prokaryotic group in terrestrial environments

Sulfate-reducing prokaryotes (SRPs) are essential microorganisms that play crucial roles in various ecological processes. Even though SRPs have been studied for over a century, there are still gaps in our understanding of their biology. In the past two decades, a significant amount of data on SRP ecology has been accumulated. This review aims to consolidate that information, focusing on SRPs in soils, their relation to the rare biosphere, uncultured sulfate reducers, and their interactions with other organisms in terrestrial ecosystems. SRPs in soils form part of the rare biosphere and contribute to various processes as a low-density population. The data reveal a diverse range of sulfate-reducing taxa intricately involved in terrestrial carbon and sulfur cycles. While some taxa like Desulfitobacterium and Desulfosporosinus are well studied, others are more enigmatic. For example, members of the Acidobacteriota phylum appear to hold significant importance for the terrestrial sulfur cycle. Many aspects of SRP ecology remain mysterious, including sulfate reduction in different bacterial phyla, interactions with bacteria and fungi in soils, and the existence of soil sulfate-reducing archaea. Utilizing metagenomic, metatranscriptomic, and culture-dependent approaches will help uncover the diversity, functional potential, and adaptations of SRPs in the global environment.

Lead or cadmium co-contamination alters benzene and toluene degrading bacterial communities

Co-contamination of hydrocarbons with heavy metals in soils often complicates and hinders bioremediation. A comprehensive characterization of site-specific degraders at contaminated sites can help determine if in situ bioremediation processes are sufficient. This study aimed to identify differences in benzene and toluene degradation rates and the microbial communities enriched under aerobic conditions when different concentrations of Cd and Pb are introduced. Microcosms were used to study the degradation of 0.23 mM benzene or 0.19 mM toluene under various concentrations of Pb (up to 240 µM) and Cd (up to 440 µM). Soil collected from a stormwater retention basin receiving runoff from a large parking lot was utilized to seed the microcosms. The hydrocarbon degradation time and rates were measured. After further rounds of amendment and degradation of benzene and toluene, 16S rRNA gene amplicon sequencing and quantitative PCR were used to ascertain the microbial communities enriched under the various concentrations of the heavy metals. The initial degradation time for toluene and benzene was 7 to 9 days and 10 to 13 days, respectively. Degradation rates were similar for each hydrocarbon despite the concentration and presence of metal co-contaminant, however, the enriched microbial communities under each condition differed. Microcosms without metal co-contaminant contained a diversity of putative benzene and toluene degrading bacteria. Cd strongly reduced the richness of the microbial communities. With higher levels of heavy metals, genera such as Ralstonia, Cupriavidus, Azoarcus, and Rhodococcus became more dominant under various conditions. The study finds that highly efficient benzene- and toluene-degrading consortia can develop under variations of heavy metal co-contamination, but the consortia are dependent on the heavy metal type and concentrations.

Material flow analysis and heavy hydrocarbon removal in a full-scale biopile and soil washing plant in northern Italy

This study aimed to assess the mass fluxes and removal efficiencies of heavy hydrocarbons in a full-scale plant located in northern Italy. This plant receives and treats contaminated soil, soils and rocks from construction and demolition activities, incineration slags and street cleaning residues. The plant has three sections, consisting of bioremediation using biopile, a soil washing stage and a stabilization/solidification unit, which can perform independently or together with the others. The material flow analysis showed how the crisis in the construction industry changed the final destination of waste after the treatment: as the market demand for coarse material decreased, waste was sent directly to landfills for inert waste, instead of being recovered. Hydrocarbon mass fluxes showed that a considerable amount of pollutants was removed. In the period 2009-2014, the removal efficiencies of the bioremediation, the soil washing section and the entire plant were respectively 73%, 58% and 62%. The percentages of removal attained at the facility in study were sufficient to ensure the possibility of recovering the waste or disposing of it in different landfill categories, according to the national regulations.

Evaluation of the physico-chemical properties of hydrocarbons-exposed bacterial biomass

In the efforts for the removal of hazardous materials from the environment biological processes are a valuable tool. Although much attention has been paid to the changes in bacteria at the omics level, another, physical-chemical perspective on the issue is essential, as little is known of microbial response to continuous exposition on harmful substances. This study provides in-depth characterization of the physical-chemical parameters of bacterial biomass after hydrocarbons exposure. To provide comparability of the harmful effects of chlorotoluenes and xylenes non-exposed and 12-months hydrocarbons exposed cells were analyzed, using the advanced spectrometric methods, inverse gas chromatography and low-temperature N2 sorption to evaluate acid-base as well as dispersive properties of the studied biomass. Presented results indicate P. fluorescens B01 cells strategy aimed at protecting the cell, thus lowering its' biodegradation efficiency as a result of metabolic stress. The outcome of the study was that prolonged exposure to pollutants might reduce the bioavailability of hydrocarbons to bacteria cells, and consequently decrease the effectiveness of decontamination of polluted sites by indigenous microorganisms.

Biodegradation potentiality of psychrophilic bacterial strain Oleispira antarctica RB-8(T)

The present study is focused on assessing the growth and hydrocarbon-degrading capability of the psychrophilic strain Oleispira antarctica RB-8(T). This study considered six hydrocarbon mixtures that were tested for 22days at two different cultivation temperatures (4 and 15°C). During the incubation period, six sub-aliquots of each culture at different times were processed for total bacterial abundance and GC-FID (gas chromatography-flame ionization detection) hydrocarbon analysis. Results from DNA extraction and DAPI (4',6-diamidino-2-phenylindole) staining showed a linear increase during the first 18days of the experiment in almost all the substrates used; both techniques showed a good match, but the difference in values obtained was approximately one order of magnitude. GC-FID results revealed a substantial hydrocarbon degradation rate in almost all hydrocarbon sources and in particular at 15°C rather than 4°C (for commercial oil engine, oily waste, fuel jet, and crude oil). A more efficient degradation was observed in cultures grown with diesel and bilge water at 4°C.

Ex-Situ Remediation Technologies for Environmental Pollutants: A Critical Perspective

Pollution and the global health impacts from toxic environmental pollutants are presently of great concern. At present, more than 100 million people are at risk from exposure to a plethora of toxic organic and inorganic pollutants. This review is an exploration of the ex-situ technologies for cleaning-up the contaminated soil, groundwater and air emissions, highlighting their principles, advantages, deficiencies and the knowledge gaps. Challenges and strategies for removing different types of contaminants, mainly heavy metals and priority organic pollutants, are also described.

Steam-treatment-based soil remediation promotes heat-tolerant, potentially pathogenic microbiota

We investigated microbiota in surface and subsurface soil from a site, above steam-treated deep sub-soil originally contaminated with chlorinated solvents. During the steam treatment, the surface soil reached temperatures c. 30 degrees C higher than the temperature in untreated soil; whereas the subsurface soil, at a depth of about 40 cm, reached a temperature c. 45 degrees C higher than untreated soil. The soil was examined prior to, during, and 6, 12, 14, 20 and 31 months after treatment. Numbers of bacteria cultivable at 42 degrees C increased significantly in subsurface soil. Similarly, substrate utilization in ECOLOG plates, incubated at 42 degrees C, increased from less than 10% of available carbon sources in the untreated soil to more than 60% of the available carbon sources in the steam-treated soil. Aspergillus fumigatus was quantified as an example ofheat-tolerant fungi normally found in compost. These organisms are rarely detected in Danish soils but high numbers (c. 10(5) hyphal forming units g(-1)) occurred in the treated soil up to 31 months after the steam-treatment. We conclude that steam-treatment leads to changes of the microbial communities. Some changes are temporary while others can last for years after termination of the steam-treatment; reflecting different strategies that soil microorganisms follow.

Impact of bacterial and fungal processes on 14C-hexadecane mineralisation in weathered hydrocarbon contaminated soil

In this study, the impact of bacterial and fungal processes on (14)C-hexadecane mineralisation was investigated in weathered hydrocarbon contaminated soil. The extent of (14)C-hexadecane mineralisation varied depending on the bioremediation strategy employed. Under enhanced natural attenuation conditions, (14)C-hexadecane mineralisation after 98 days was 8.5 ± 3.7% compared to <1.2% without nitrogen and phosphorus additions. (14)C-hexadecane mineralisation was further enhanced through Tween 80 amendments (28.9 ± 2.4%) which also promoted the growth of a Phanerochaete chyrsosporium fungal mat. Although fungal growth in weathered hydrocarbon contaminated soil could be promoted through supplementing additional carbon sources (Tween 80, sawdust, compost, pea straw), fungal (14)C-hexadecane mineralisation was negligible when sodium azide was added to soil microcosms to inhibit bacterial activity. In contrast, when fungal activity was inhibited through nystatin additions, (14)C-hexadecane mineralisation ranged from 6.5 ± 0.2 to 35.8 ± 3.8% after 98 days depending on the supplied amendment. Bacteria inhibition with sodium azide resulted in a reduction in bacterial diversity (33-37%) compared to microcosms supplemented with nystatin or microcosms without inhibitory supplements. However, alkB bacterial groups were undetected in sodium azide supplemented microcosms, highlighting the important role of this bacterial group in (14)C-hexadecane mineralisation.