Design and field-scale implementation of an "on site" bioremediation treatment in PAH-polluted soil

Brownfield-related studies in the context of climate change: A comprehensive review and future prospects

The global climate change events are expected to augment the vulnerability of persistent organic pollutants within the global brownfield areas to a certain extent, consequently heightening the risk crises faced by these brownfields amidst the backdrop of global environmental changes. However, studies addressing brownfield risks from the perspective of climate change have received limited attention. Nonetheless, the detrimental consequences of brownfield risks are intrinsically linked to strategies for mitigating and adapting to sustainable urban development, emphasizing the critical importance of their far-reaching implications. This relevance extends to concerns about environmental quality, safety, health risks, and the efficacy of chosen regeneration strategies, including potential secondary pollution risks. This comprehensive review systematically surveys pertinent articles published between 1998 and 2023. A selective analysis was conducted on 133 articles chosen for their thematic relevance. The findings reveal that: (1) Under the backdrop of the climate change process, brownfield restoration is necessitated to provide scientific and precise guidance. The integration of brownfield considerations with the dynamics of climate change has progressively evolved into a unified framework, gradually shaping a research paradigm characterized by "comprehensive + multi-scale + quantitative" methodologies; (2) Research themes coalesce into five prominent clusters: "Aggregation of Brownfield Problem Analysis", "Precision Enhancement of Brownfield Identification through Information Technology", "Diversification of Brownfield Reutilization Assessment", "Process-Oriented Approaches to Brownfield Restoration Strategies", and "Expansion of Ecological Service Functions in Brownfield Contexts"; (3) Application methodologies encompass five key facets: "Temporal and Spatial Distribution Patterns of Pollutants", "Mechanisms and Correlations of Pollution Effects", "Evaluation of Pollution Risks", "Assessment of Brownfield Restoration Strategies", and "Integration of Brownfield Regeneration with Spatial Planning". Future brownfield research from the climate change perspective is poised to reflect characteristics such as "High-Precision Prediction, Comprehensive Dimensionality, Full-Cycle Evaluation, Low-Risk Exposure, and Commitment to Sustainable Development".

Bioremediation of polycyclic aromatic hydrocarbons: An updated microbiological review

A class of organic priority pollutants known as PAHs is of critical public health and environmental concern due to its carcinogenic properties as well as its genotoxic, mutagenic, and cytotoxic properties. Research to eliminate PAHs from the environment has increased significantly due to awareness about their negative effects on the environment and human health. Various environmental factors, including nutrients, microorganisms present and their abundance, and the nature and chemical properties of the PAH affect the biodegradation of PAHs. A large spectrum of bacteria, fungi, and algae have ability to degrade PAHs with the biodegradation capacity of bacteria and fungi receiving the most attention. A considerable amount of research has been conducted in the last few decades on analyzing microbial communities for their genomic organization, enzymatic and biochemical properties capable of degrading PAH. While it is true that PAH degrading microorganisms offer potential for recovering damaged ecosystems in a cost-efficient way, new advances are needed to make these microbes more robust and successful at eliminating toxic chemicals. By optimizing some factors like adsorption, bioavailability and mass transfer of PAHs, microorganisms in their natural habitat could be greatly improved to biodegrade PAHs. This review aims to comprehensively discuss the latest findings and address the current wealth of knowledge in the microbial bioremediation of PAHs. Additionally, recent breakthroughs in PAH degradation are discussed in order to facilitate a broader understanding of the bioremediation of PAHs in the environment.

The microbiome of a brownfield highly polluted with mercury and arsenic

Abandoned brownfields represent a challenge for their recovery. To apply sustainable remediation technologies, such as bioremediation or phytoremediation, indigenous microorganisms are essential agents since they are adapted to the ecology of the soil. Better understanding of microbial communities inhabiting those soils, identification of microorganisms that drive detoxification process and recognising their needs and interactions will significantly improve the outcome of the remediation. With this in mind we have carried out a detailed metagenomic analysis to explore the taxonomic and functional diversity of the prokaryotic and eukaryotic microbial communities in soils, several mineralogically distinct types of pyrometallurgic waste, and groundwater sediments of a former mercury mining and metallurgy site which harbour very high levels of arsenic and mercury pollution. Prokaryotic and eukaryotic communities were identified, which turned out to be more diverse in the surrounding contaminated soils compared to the pyrometallurgic waste. The highest diversity loss was observed in two environments most contaminated with mercury and arsenic (stupp, a solid mercury condenser residue and arsenic-rich soot from arsenic condensers). Interestingly, microbial communities in the stupp were dominated by an overwhelming majority of archaea of the phylum Crenarchaeota, while Ascomycota and Basidiomycota fungi comprised the fungal communities of both stump and soot, results that show the impressive ability of these previously unreported microorganisms to colonize these extreme brownfield environments. Functional predictions for mercury and arsenic resistance/detoxification genes show their increase in environments with higher levels of pollution. Our work establishes the bases to design sustainable remediation methods and, equally important, to study in depth the genetic and functional mechanisms that enable the subsistence of microbial populations in these extremely selective environments.

Enhancement of nitrogen fixation and diazotrophs by long-term polychlorinated biphenyl contamination in paddy soil

Biological nitrogen fixation (BNF) driven by diazotrophs is a major means of increasing available nitrogen (N) in paddy soil, in addition to anthropogenic fertilization. However, the influence of long-term polychlorinated biphenyl (PCB) contamination on the diazotrophic community and nitrogen fixation in paddy soil is poorly understood. In this study, samples were collected from paddy soil subjected to > 30 years of PCB contamination, and the soil diazotrophic community and N₂ fixation rate were evaluated by Illumina MiSeq sequencing and acetylene reduction assays, respectively. The results indicated that high PCB contamination increased diazotrophic abundance and the N₂ fixation rate, and altered diazotrophic community structure in the paddy soil. The random forest model demonstrated that the β-diversity of the diazotrophic community was the most significant predictor of the N₂ fixation rate. Structure equation modeling identified a specialized keystone diazotrophic ecological cluster, predominated by Bradyrhizobium, Desulfomonile, and Cyanobacteria, as the key driver of N₂ fixation. Overall, our findings indicated that long-term PCB contamination enhanced the N₂ fixation rate by altering diazotrophic community abundance and structure, which may deepen our understanding of the ecological function of diazotrophs in organic-contaminated soil.

Effective bioremediation of soil from the Burgan oil field (Kuwait) using compost: A comprehensive hydrocarbon and DNA fingerprinting study

An innovative combination of metagenomic profiling of microbial communities and GC-MS & Pyrolysis-GC-MS fingerprinting methods were used to assess the biodegradation of contaminated soil from the Burgan oil field in Kuwait. The soil was treated with (sludge) compost in microcosms to evaluate the feasibility of this material for bioremediation purposes. The most favourable trial showed a > 80% decrease in TPH, thereby indicating strong potential for full-scale application using a cost-effective technology and thus in line with the principles of the circular economy. The microbial study showed that compost addition enhanced the organic matter and nutrient content of the soil. However, the microorganisms in the compost did not seem to play a relevant role in bioremediation, meaning that compost amendments serve as a biostimulation rather than a bioaugmentation approach. The chemical study of the distinct oil fractions revealed rapidly biodegraded compounds (alkanes, alkyl-aromatics, etc.) and others that were much more refractory (hopanes, benzohopanes, etc.). Of note, although heavy fractions are usually considered recalcitrant to biodegradation, we observed incipient degradation of the asphaltene fraction by means of double-shot thermodesorption and pyrolysis. Finally, chemical fingerprinting also revealed that the treated soil contained some of the compounds found in the compost, such as coprostanol, cholesterol, and plant sterols. This observation would support the use of these compounds as proxies to monitor the effects of compost and to adjust dosages in real-scale bioremediation treatments.

Burkholderia vietnamiensis G4 as a biological agent in bioremediation processes of polycyclic aromatic hydrocarbons in sludge farms

Polycyclic aromatic hydrocarbons (PAHs) are one of the main pollutants generated by the refining and use of oil. To search bioremediation alternatives for these compounds, mainly in situ, considering the biotic and abiotic variables that affect the contaminated sites is determinant for the success of bioremediation techniques. In this study, bioremediation strategies were evaluated in situ, including biostimulation and bioaugmentation for 16 priority PAHs present in activated sludge farms. B. vietnamiensis G4 was used as a biodegradation agent for bioaugmentation tests. The analyses occurred for 12 months, and temperature and humidity were measured to verify the effects of these factors on the biodegradation. We used the technique GC-MS to evaluate and quantify the degradation of PAHs over the time of the experiment. Of the four treatments applied, bioaugmentation with quarterly application proved to be the best strategy, showing the degradation of compounds of high (34.4% annual average) and low (21.9% annual average) molecular weight. A high degradation rate for high molecular weight compounds demonstrates that this technique can be successfully applied in bioremediation of areas with compounds considered toxic and stable in nature, contributing to the mitigation of impacts generated by PAHs.

The relationships between soil physicochemical properties, bacterial communities and polycyclic aromatic hydrocarbon concentrations in soils proximal to coking plants

Microbial degradation of polycyclic aromatic hydrocarbons (PAHs) is the major channel for their decontamination from different environments. Aerobic and anaerobic biodegradations of PAHs in batch reactors with single or multiple bacterial strains have been intensively studied, but the cooperative mechanism of functional PAH-degrading populations at the community level under field conditions remains to be explored. We determined the composition of PAH-degrading populations in the bacterial community and PAHs in farmland and wasteland soils contaminated by coking plants using high-throughput sequencing and high-performance liquid chromatography (HPLC), respectively. The results indicated that the PAH content of farmland was significantly lower than that of wasteland, which was attributed to the lower content of low molecular weight (LMW) PAHs and benzo [k]fluoranthene. The soil physicochemical properties were significantly different between farmland and wasteland. The naphthalene content was related to the soil organic carbon (SOC) and pH, while phenanthrene was related to the nitrate nitrogen (NO₃^--N) and water content (WC). The pH, nitrite (NO₂^--N), SOC, NO₃^--N and WC were correlated with the content of high molecular weight (HMW) PAHs and total PAHs. The relative abundances of the phyla Actinobacteria, Chloroflexi, Acidobacteria, and Firmicutes and the genera Nocardioides, Bacillus, Lysobacter, Mycobacterium, Streptomyces, and Steroidobacter in farmland soil were higher than those in wasteland soil. The soil physicochemical characteristics of farmland increased the diversities of the PAH degrader and total bacterial communities, which were significantly negatively related to the total PAHs and LMW PAHs. Subsequently, the connectivity and complexity of the network in farmland were lower than those in wasteland, while the module containing a module hub capable of degrading PAHs was identified in the network of farmland soil. Structural equation modelling (SEM) analysis showed that the soil characteristics and optimized abundance and diversity of the bacterial community in farmland were beneficial for the dissipation efficiency of PAHs.

Nitrogen addition facilitates phytoremediation of PAH-Cd cocontaminated dumpsite soil by altering alfalfa growth and rhizosphere communities

Thousands of unlined landfills and open dumpsites seriously threatened the safety of soil and groundwater due to leachate leakage with a mass of pollutants, particularly heavy metals, organic contaminants and ammonia. Phytoremediation is widely used in the treatment of cocontaminated soils because it is cost-effective and environmentally friendly. However, the extent to which phytoremediation efficiency and plant physiological responses are affected by the high nitrogen (N) content in such cocontaminated soil is still uncertain. Here, pot experiments were conducted to investigate the effects of N addition on the applicability of legume alfalfa remediation for polycyclic aromatic hydrocarbon‑cadmium (PAHCd) co-/contaminated soil and the corresponding microbial regulation mechanism. The results showed that the PAH dissipation rates and Cd removal rates in the high-contamination groups increased with the external N supply, among which the pyrene dissipation rates in the cocontaminated soil was elevated most significantly, from 78.10% to 87.25%. However, the phytoremediation efficiency weakened in low cocontaminated soil, possibly because the excessive N content had inhibitory effects on the rhizobium Ensifer and restrained alfalfa growth. Furthermore, the relative abundance of PAH-degrading bacteria in the rhizosphere dominated PAH dissipation. As reflected by principal coordinate analysis (PCoA) analysis and hierarchical dendrograms, the microbial community composition changed with N addition, and a more pronounced shift was found in the rhizosphere relative to the endosphere or shoots of alfalfa. This study will provide a theoretical basis for legume plant remediation of dumpsites as well as soil contaminated with multiple pollutants.

Pilot-scale bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil using an indigenous bacterial consortium in soil-slurry bioreactors

Soil-slurry bioreactor based bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil was studied through laboratory and pilot-scale trials, in which the degradation mechanism was explored. Indigenous PAH-degrading consortium was firstly screened out and it degraded 80.5% of total PAHs in lab-scale bioreactors. Then a pilot-scale trial lasting 410 days was conducted in two bioreactors of 1.5 m³ to examine the operating parameters and validate the optimum running conditions. During the initial 200 days, the crucial running parameters affecting PAH removal were evaluated and selected. Subsequently, an average PAH removal rate of 93.4% was achieved during 15 consecutive batches (210 days) under the optimum running conditions. The kinetic analysis showed that the reactor under optimum conditions achieved the highest PAH degradation rate of 0.1795 day^-1 and the shortest half-life of 3.86 days. Notably, efficient mass transfer of PAHs and high biodegradation capability by bioaugmented consortia in soil-slurry bioreactors were two key mechanisms for appreciable PAH removal performance. Under the optimal operating conditions, the degradation rate of low-molecular-weight (LMW) PAHs was significantly higher than high-molecular-weight (HMW) PAHs; when the mass transfer was limited, there was no significant difference between their degradation behaviors. Both microbial co-metabolism and collaborative metabolism might occur when all PAHs demonstrated low degradation rates. The findings provide insightful guidance on the future assessment and remediation practices of PAH-contaminated sites.

Salicylate or Phthalate: The Main Intermediates in the Bacterial Degradation of Naphthalene

Polycyclic aromatic hydrocarbons (PAHs) are widely presented in the environment and pose a serious environmental threat due to their toxicity. Among PAHs, naphthalene is the simplest compound. Nevertheless, due to its high toxicity and presence in the waste of chemical and oil processing industries, naphthalene is one of the most critical pollutants. Similar to other PAHs, naphthalene is released into the environment via the incomplete combustion of organic compounds, pyrolysis, oil spills, oil processing, household waste disposal, and use of fumigants and deodorants. One of the main ways to detoxify such compounds in the natural environment is through their microbial degradation. For the first time, the pathway of naphthalene degradation was investigated in pseudomonades. The salicylate was found to be a key intermediate. For some time, this pathway was considered the main, if not the only one, in the bacterial destruction of naphthalene. However, later, data emerged which indicated that gram-positive bacteria in the overwhelming majority of cases are not capable of the formation/destruction of salicylate. The obtained data made it possible to reveal that protocatechoate, phthalate, and cinnamic acids are predominant intermediates in the destruction of naphthalene by rhodococci. Pathways of naphthalene degradation, the key enzymes, and genetic regulation are the main subjects of the present review, representing an attempt to summarize the current knowledge about the mechanism of the microbial degradation of PAHs. Modern molecular methods are also discussed in the context of the development of “omics” approaches, namely genomic, metabolomic, and proteomic, used as tools for studying the mechanisms of microbial biodegradation. Lastly, a comprehensive understanding of the mechanisms of the formation of specific ecosystems is also provided.

Remediation of soils and sediments polluted with polycyclic aromatic hydrocarbons: To immobilize, mobilize, or degrade?

Polycyclic aromatic hydrocarbons (PAHs) are generated due to incomplete burning of organic substances. Use of fossil fuels is the primary anthropogenic cause of PAHs emission in natural settings. Although several PAH compounds exist in the natural environmental setting, only 16 of these compounds are considered priority pollutants. PAHs imposes several health impacts on humans and other living organisms due to their carcinogenic, mutagenic, or teratogenic properties. The specific characteristics of PAHs, such as their high hydrophobicity and low water solubility, influence their active adsorption onto soils and sediments, affecting their bioavailability and subsequent degradation. Therefore, this review first discusses various sources of PAHs, including source identification techniques, bioavailability, and interactions of PAHs with soils and sediments. Then this review addresses the remediation technologies adopted so far of PAHs in soils and sediments using immobilization techniques (capping, stabilization, dredging, and excavation), mobilization techniques (thermal desorption, washing, electrokinetics, and surfactant assisted), and biological degradation techniques. The pros and cons of each technology are discussed. A detailed systematic compilation of eco-friendly approaches used to degrade PAHs, such as phytoremediation, microbial remediation, and emerging hybrid or integrated technologies are reviewed along with case studies and provided prospects for future research.

Succession of microbial communities and synergetic effects during bioremediation of petroleum hydrocarbon-contaminated soil enhanced by chemical oxidation

Biotechnologies integrated with chemical techniques are promising in treating the soils contaminated by petroleum hydrocarbons. Experiments by applying the degrading consortium and the modified Fenton (MF) with the chelator sodium citrate simultaneously were carried out to investigate the effects of the MF reagents on the degradation of total petroleum hydrocarbons (TPHs), changes in enzyme activities and the succession of microbial communities at the 0, 20, 100 and 500 mmol/kg hydrogen peroxide concentration levels. The ratio between hydrogen peroxide, ferrous sulfate and sodium citrate in the MF reagents was 100:1:1. The results indicated that the degradation of TPHs conformed to first-order kinetics and MF treatments increased the total removal rates of TPHs (4.73-24.26%) and activated dehydrogenase and polyphenol oxidase activities. A shift in microbial communities from Proteobacteria to Bacteroidetes was observed during the enhanced bioremediation, and the predominant genus shifted from Pseudomonas with an average relative abundance (ARAs) of 76.61% at the beginning to Sphingobacterium with ARAs of 52.06% at the later stage. The MF reagents at the proper level could simplify the relationship among the community populations, alleviate their competition and strengthen their associations, which would optimize the removal efficiency.

Soil microbial community succession and interactions during combined plant/white-rot fungus remediation of polycyclic aromatic hydrocarbons

Despite combined plant/white-rot fungus remediation being effective for remediating polycyclic aromatic hydrocarbon (PAH)-contaminated soil, the complex organismal interactions and their effects on soil PAH degradation remain unclear. Here, we used quantitative PCR, analysis of soil enzyme activities, and sequencing of representative genes to characterize the ecological dynamics of natural attenuation, mycoremediation (MR, using Crucibulum laeve), phytoremediation (PR, using Salix viminalis), and plant-microbial remediation (PMR, using both species) for PAHs in soil for 60 days. On day 60, PMR achieved the highest removal efficiency of all three representative PAHs (65.5%, 47.5%, and 62.4% for phenanthrene, pyrene, and benzo(a)pyrene, respectively) when compared with the other treatments. MR significantly increased the relative abundance of Rhizobium and Bacillus but antagonized the other putative indigenous PAH-degrading bacteria, which were enriched by PR. PR significantly reduced soil nutrients, such as NO₃^- and NH₄⁺, and available potassium (AK), thereby changing the microbial community composition as reflected by redundancy analysis, significantly reducing the soil bacterial biomass relative to that in other treatments. These disadvantages hampered phenanthrene and pyrene removal. MR provided additional nutrients, which counteracted the nutrient consumption associated with PR, thereby maintaining the microbial community diversity and bacterial biomass of PMR at a level achieved in the NA treatment. Combination remediation therefore overcame the disadvantages of using PR alone. These results indicated that inoculation with the combination of S. viminalis and C. laeve synergistically stimulated the growth of indigenous PAH-degrading microorganisms and maintained bacterial biomass, thus accelerating the dissipation of soil PAHs.

Bioaugmentation Treatment of a PAH-Polluted Soil in a Slurry Bioreactor

A bioslurry reactor was designed and used to treat loamy clay soil polluted with polycyclic aromatic hydrocarbons (PAHs). To this end, biostimulation alone, or combined with bioaugmentation with two bacterial strains (Rhodocccus erythropolis and Pseudomonas stuzeri) previously isolated from the polluted site, was applied. The PAH concentrations decreased notably after 15 days in all of the treatments. The concentrations of the two- and three-ring compounds fell by >80%, and, remarkably, the four- to six-ring PAHs also showed a marked decrease (>70%). These results thus indicate the capacity of bioslurry treatments to improve, notably, the degradation yields obtained in a previous real-scale remediation carried out using biopiles. In this sense, the remarkable results for recalcitrant PAHs can be attributed to the increase pollutants’ bioavailability achieves in the slurry bioreactors. Regarding bioaugmentation, although treatment with R. erythropolis led to a somewhat greater reduction of lighter PAHs at 15 days, the most time-effective treatment was achieved using P. stutzeri, which led to an 84% depletion of total PAHs in only three days. The effects of microbial degradation of other organic compounds were also monitored by means of combined qualitative and quantitative gas chromatography mass spectrometry (GC–MS) tools, as was the evolution of microbial populations, which was analyzed by culture and molecular fingerprinting experiments. On the basis of our findings, bioslurry technology emerges as a rapid and operative option for the remediation of polluted sites, especially for fine soil fractions with a high load of recalcitrant pollutants.

Effects of biochar and organic substrates on biodegradation of polycyclic aromatic hydrocarbons and microbial community structure in PAHs-contaminated soils

A incubation experiment was conducted to investigate whether combined amendment of biochar (B) and compost (CP), mushroom residue (M) and corn straw (Y) could enhance biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. After 77 days of incubation, both B + M and B + Y significantly (p < 0.01) increased removal rate of PAHs compared with amendment of biochar alone. However, B+CP resulted in a significant (p < 0.01) decreasing of PAHs removal. Compared with no biochar and no organic substrates addition (CK) and B, both B+M and B+Y significantly (p < 0.01) enhanced concentrations of dissolved organic carbon (DOC) and were favorable for the microbial growth reflected by microbial biomass carbons (MBC) and emission of carbon dioxide. Redundancy analysis (RDA) indicated that B + CP, B + M and B + Y separated the bacterial community compared with CK and B. However, the community composition structure in B + CP was different from that of B + M and B + Y. Moreover, the abundance of some PAHs degraders and PAH degradation genes predicted by PICRUSt software was promoted by B + M or B + Y, whereas that was inhibited under B + CP. The present study suggested that both B + M and B + Y could accelerate biodegradation of PAHs mainly through increasing the concentration of DOC and the abundances of microbial PAH degraders in soils.

Synergistic biodegradation of phenanthrene and fluoranthene by mixed bacterial cultures

Polycyclic aromatic hydrocarbons (PAHs) are highly recalcitrant compounds and difficult to degrade. Therefore in this work, using a bioremediation approach, mixed bacterial cultures (ASPF) was developed and enriched from polluted marine sediments capable of degrading 400 mg/L of phenanthrene and fluoranthene in Bushnell Hass medium. ASPF consists of 22 bacterial genera dominated by Azoarcus and Chelativorans. The biostimulation effect of three water soluble fertilizers (NPK, urea, and ammonium sulfate) showed that NPK and ammonium sulfate have enhanced the degradation, whereas urea has decreased their degradation. ASPF was also able to degrade phenanthrene and fluoranthene in the presence of petroleum hydrocarbons. But degradation was found to decrease in the presence of pathway intermediates (phthalic acid and catechol) due to enzymatic feedback inhibition. Optimum degradation of both PAHs was observed under room temperature, suggesting the practical applicability of ASPF.

Comparison of zero-valent iron and iron oxide nanoparticle stabilized alkyl polyglucoside phosphate foams for remediation of diesel-contaminated soils

Stable surfactant foam might play a vital role in the effective remediation of diesel oil contaminated soil-a major environmental hazard. This paper, first of its kind, is reporting the remediation of diesel-contaminated desert soil, coastal soil and clay soil by aqueous alkylpolyglucoside phosphate (APG-Ph) surfactant foams stabilized by Fe⁰ and Fe₃O₄ nanoparticles. Zero-valent iron (Fe⁰, ∼28 nm) and iron oxide (Fe₃O₄, ∼20 nm) nanoparticles are synthesized by liquid-phase reduction and precipitation methods, respectively. The effect of these nanoparticles on foamability, foam stability, surface tension and remediation of diesel-contaminated soils are examined at various concentrations (volume %) of alkylpolyglucoside phosphate (APG-Ph) surfactant and nanoparticles (mg/l). The maximum values of foamability and foam stability recorded for 0.1 vol % APG-Ph foam stabilized by 3.5 mg/l Fe⁰ are 108.3 and 110.4 mL, respectively. At the same conditions, the Fe₃O₄ results in 99.4 and 87.5 mL, respectively, depicting the better performance of Fe⁰. Reduction in surface tension of 0.1 vol % APG-Ph solution (50.75 mN/m) with the addition of 3.5 mg/l Fe⁰ (9.51 mN/m) and Fe₃O₄ (19.45 mN/m) nanoparticle is observed. Both the nanoparticles enhance remediation. The foam formed with 0.1 vol % APG-Ph and stabilized by 3.5 mg/l Fe⁰ shows the maximum diesel removal efficiency of 95.3, 94.6, and 57.5% for coastal soil, desert soil and clay soil, respectively. On the other hand, Fe₃O₄ (3.5 mg/l) stabilized APG-Ph foam of the same concentration shows merely 76.0, 79.6 and 51.6% diesel removal efficiency for coastal soil, desert soil, and clay soil, respectively. The rate of diesel removal by zero-valent iron and iron oxide nanoparticle stabilized foams are found to be well described by the first order kinetic model. Higher foamability, foam stability, and reducing capacity accompanying lower surface tension, compared to those of the Fe₃O₄ nanoparticle stabilized foam, could explain higher diesel removal efficiency of the Fe⁰ nanoparticle stabilized foam.

Nature based solutions for contaminated land remediation and brownfield redevelopment in cities: A review

Urban industrialization has caused severe land contamination at hundreds of thousands of sites in cities all around the world, posing a serious health risk to millions of people. Many contaminated brownfield sites are being left abandoned due to the high cost of remediation. Traditional physical and chemical remediation technologies also require high energy and resource input, and can result in loss of land functionality and cause secondary pollution. Nature-based solutions (NBS) including phytoremediation and conversion of brownfield sites to public greenspaces, holds much promise in maximizing a sustainable urban renaissance. NBS is an umbrella concept that can be used to capture nature based, cost effective and eco-friendly treatment technologies, as well as redevelopment strategies that are socially inclusive, economically viable, and with good public acceptance. The NBS concept is novel and in urgent need of new research to better understand the pros and cons, and to enhance its practicality. This review article summarizes NBS's main features, key technology choices, case studies, limitations, and future trends for urban contaminated land remediation and brownfield redevelopment.

Use of bacterial acc deaminase to increase oil (especially poly aromatic hydrocarbons) phytoremediation efficiency for maize (zea mays) seedlings

Oil presence in soil, as a stressor, reduces phytoremediation efficiency through an increase in the plant stress ethylene. Bacterial 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, as a plant stress ethylene reducer, was employed to increase oil phytoremediation efficiency. For this purpose, the ability of ACC deaminase-producing Pseudomonas strains to grow in oil-polluted culture media and withstand various concentrations of oil and also their ability to reduce plant stress ethylene and enhance some growth characteristics of maize and finally their effects on increasing phytoremediation efficiency of poly aromatic hydrocarbons (PAHs) in soil were investigated. Based on the results, of tested strains just P9 and P12 were able to perform oil degradation. Increasing oil concentration from 0 to 10% augmented these two strains population, 15.7% and 12.9%, respectively. The maximum increase in maize growth was observed in presence of P12 strain. Results of high-performance liquid chromatography (HPLC) revealed that PAHs phytoremediation efficiency was higher for inoculated seeds than uninoculated. The highest plant growth and PAHs removal percentage (74.9%) from oil-polluted soil was observed in maize inoculated with P12. These results indicate the significance of ACC deaminase producing bacteria in alleviation of plant stress ethylene in oil-polluted soils and increasing phytoremediation efficiency of such soils.

Preliminary study of phytoremediation of brownfield soil contaminated by PAHs

Our project was aimed at improving a brownfield in the city of Kladno, where an old steel producing facility used to be in operation. Ecological risk is mainly caused by the processing of co-products during coal production (tars, oils). Knowledge of toxicology and environmental aspects can help us protect human health and the environment. Primarily, we focused on soil sampling and identification of pollutants. Results showed that organic contamination on the site is very high. Average concentration of total petroleum carbon in the soil was about 13g/kg DW, which is much more than the maximum allowed concentration. For selection of suitable plant species for phytoremediation at the site, experiments were conducted in a greenhouse. Biomass growth, root morphology, and pigment content in the leaves of Brassica napus var. Opus-C1 and Sorghum×drummondii var. Honey Graze BMR plants were studied. Plant analysis confirmed that polyaromatic hydrocarbons (PAHs) accumulated in the shoots of both plant species. B. napus plants grown on Poldi soil in a greenhouse were able to survive the toxicity of PAHs in soil, and their ability to accumulate PAHs from soil was evident. However, more studies are needed to decide if the plants are usable for phytoremediation of this brownfield.

Removal of Two High Molecular Weight PAHs from Soils with Different Water Content

Polycyclic aromatic hydrocarbons (PAHs) such as benz[a]anthracene (BA) and dibenz[a,h]anthracene (DBA), which are considered toxic, are frequently found in contaminated soils in Mexico. A laboratory-scale study monitored the degradation of the mixture of these two PAHs in three soils from different Mexican states (Tabasco, Morelos and Veracruz), each with different organic matter content, particle size distribution and incubated under different water content conditions. The hydrocarbons were extracted using microwave digestion and quantified by GC/MS. The removal of the PAHs, the growth of aerobic bacteria and microbial activity were determined in soil samples with and without a bacterial growth inhibitor (HgCl₂). The conclusion is that more than 90% of both contaminants was removed from the three soils, independently of the soil water content or the application of a bacterial growth inhibitor. Biological properties of the soils showed changes at the end of the experiment, but the results of the removal of PAHs were similar in the three soils.

Soil and brownfield bioremediation

Soil contamination with petroleum hydrocarbons, persistent organic pollutants, halogenated organic chemicals and toxic metal(loid)s is a serious global problem affecting the human and ecological health. Over the past half‐century, the technological and industrial advancements have led to the creation of a large number of brownfields, most of these located in the centre of dense cities all over the world. Restoring these sites and regeneration of urban areas in a sustainable way for beneficial uses is a key priority for all industrialized nations. Bioremediation is considered a safe economical, efficient and sustainable technology for restoring the contaminated sites. This brief review presents an overview of bioremediation technologies in the context of sustainability, their applications and limitations in the reclamation of contaminated sites with an emphasis on brownfields. Also, the use of integrated approaches using the combination of chemical oxidation and bioremediation for persistent organic pollutants is discussed.

Effects of different agricultural wastes on the dissipation of PAHs and the PAH-degrading genes in a PAH-contaminated soil

Land application of agricultural wastes is considered as a promising bioremediation approach for cleaning up soils contaminated by aged polycyclic aromatic hydrocarbons (PAHs). However, it remains largely unknown about how microbial PAH-degraders, which play a key role in the biodegradation of soil PAHs, respond to the amendments of agricultural wastes. Here, a 90-day soil microcosm study was conducted to compare the effects of three agricultural wastes (i.e. WS, wheat stalk; MCSW, mushroom cultivation substrate waste; and CM, cow manure) on the dissipation of aged PAHs and the abundance and community structure of PAH-degrading microorganisms. The results showed that all the three agricultural wastes accelerated the dissipation of aged PAHs and significantly increased abundances of the bacterial 16S rRNA and PAH-degrading genes (i.e. pdo1 and nah). CM and MCSW with lower ratios of C:N eliminated soil PAHs more efficiently than WS with a high ratio of C:N. Low molecular weight PAHs were dissipated more quickly than those with high molecular weight. Phylogenetic analysis revealed that all of the nah and C12O clones were affiliated within Betaproteobacteria and Gammaproteobacteria, and application of agricultural wastes significantly changed the community structure of the microorganisms harboring nah and C12O genes, particularly in the CM treatment. Taken together, our findings suggest that the three tested agricultural wastes could accelerate the degradation of aged PAHs most likely through changing the abundances and community structure of microbial PAH degraders.

Application of spent mushroom (Lentinula edodes) substrate and acclimated sewage sludge on the bioremediation of polycyclic aromatic hydrocarbon polluted soil

A novel technology for remediation and improvement of soil was provided along with a new approach for waste recycling.

Diversity of organotrophic bacteria, activity of dehydrogenases and urease as well as seed germination and root growth Lepidium sativum, Sorghum saccharatum and Sinapis alba under the influence of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons are organic compounds with highly toxic, carcinogenic, and mutagenic properties, which adversely affect the basic biological parameters of the soil, including the count of microorganisms, and the enzymatic activity. In addition to disturbances to the biological activity of the soil, PAHs may also exhibit toxic effects on plants. In view of the above, the study involved testing aimed at the determination of the effects of polycyclic aromatic hydrocarbons in a form of naphthalene, phenanthrene, anthracene and pyrene on the count, colony development (CD) index, ecophysiological (EP) diversity index of organotrophic bacteria, and the activity of soil dehydrogenases and soil urease. Moreover, an attempt was made to determine the soil's resistance based on the activity of the above-listed enzymes, and the effect of polycyclic aromatic hydrocarbons on seed germination and root growth was assessed by Lepidium sativum, Sorghum saccharatum, and Sinapis alba. In addition, the species of bacteria found in a soil subjected to strong pressure of polycyclic aromatic hydrocarbons were isolated. The experiment was performed in a laboratory on samples of loamy sand. Polycyclic aromatic hydrocarbons were introduced into the soil in an amount of 0, 1000, 2000, and 4000 mg kg(-1) of soil dry matter. Germination and growth of cress (L. sativum), white mustard (S. alba), and sweet sorghum (S. saccharatum) were determined using Phytotoxkit tests. It was found that the tested PAHs increased the average colony counts of organotrophic soil bacteria; pyrene did so to the greatest extent (2.2-fold relative to non-contaminated soil), phenanthrene to the smallest extent (1.4-fold relative to non-contaminated soil). None of the PAHs changed the value of the bacterial colony development (CD) index, while anthracene and pyrene increased the value of the eco-physiological (EP) diversity indicator. PAHs lowered the activity of the tested enzymes. The activity of dehydrogenases was dependent on a greater extent by the type of hydrocarbon (54.56%) rather than by the dose (10.64%), while for the activity of urease, it was the opposite. The greater extent was dependent on dose (95.42%) rather than by type (0.21%). Dehydrogenases are characterised by greater resistance to the action of PAHs than urease. Based on seed germination and root growth, it has shown that S. alba is best suited, being the most vulnerable plant, while S. saccharatum is the least suited. Subjecting a soil to strong pressure of PAHs leads to disturbances to the biological parameters of the soil, seed germination, and root growth L. sativum, S. saccharatum, and S. alba.

Implications of polluted soil biostimulation and bioaugmentation with spent mushroom substrate (Agaricus bisporus) on the microbial community and polycyclic aromatic hydrocarbons biodegradation

Different applications of spent Agaricus bisporus substrate (SAS), a widespread agro-industrial waste, were investigated with respect to the remediation of a historically polluted soil with Polycyclic Aromatic Hydrocarbons (PAH). In one treatment, the waste was sterilized (SSAS) prior to its application in order to assess its ability to biostimulate, as an organic amendment, the resident soil microbiota and ensuing contaminant degradation. For the other treatments, two bioaugmentation approaches were investigated; the first involved the use of the waste itself and thus implied the application of A. bisporus and the inherent microbiota of the waste. In the second treatment, SAS was sterilized and inoculated again with the fungus to assess its ability to act as a fungal carrier. All these treatments were compared with natural attenuation in terms of their impact on soil heterotrophic and PAH-degrading bacteria, fungal growth, biodiversity of soil microbiota and ability to affect PAH bioavailability and ensuing degradation and detoxification. Results clearly showed that historically PAH contaminated soil was not amenable to natural attenuation. Conversely, the addition of sterilized spent A. bisporus substrate to the soil stimulated resident soil bacteria with ensuing high removals of 3-ring PAH. Both augmentation treatments were more effective in removing highly condensed PAH, some of which known to possess a significant carcinogenic activity. Regardless of the mode of application, the present results strongly support the adequacy of SAS for environmental remediation purposes and open the way to an attractive recycling option of this waste.

Enhanced bioremediation of soil from Tianjin, China, contaminated with polybrominated diethyl ethers

This work aimed to evaluate the effectiveness of nutrients, H2O2, and tourmaline on the bioremediation of fields where the soil was contaminated with polybrominated diethyl ethers (PBDEs). The results showed that 39.2, 38.3, and 48.1 % of total PBDE removal was observed in microcosms with the addition of nutrients, such as NaNO3, NH4Cl, and NH4NO3, respectively, compared to only 15.2 and 5.8 % of PBDE removal from soil with added Aspergillus niger and control soil, respectively, after 50 days of incubation. In addition, 50.8 and 56.5 % of total PBDE removal were observed in microcosms with 0.5 and 1 μL H2O2. The addition of tourmaline increased total PBDE removal to 32.4 %. Significant increases in soil enzymatic activity with PBDE degraders and bacterial communities were observed using polymerase chain reaction (PCR)--denaturing gradient gel electrophoresis (DGGE). These observations suggested that the combination of inorganic nutrients with chemical, mineral, and biological treatment could improve the PBDE removal efficiency. However, the combination of H2O2 and biological treatment processes is the most efficient technology. This combination of technologies would not cause adverse effects on the subsequent bioremediation process. Therefore, this work offers a potential alternative for the remediation of soil contaminated with PBDE pollutants.