Bioremediation of chlorophenol-contaminated sawmill soil using pilot-scale bioreactors under consecutive anaerobic-aerobic conditions

Biodegradation of aliphatic polyurethane foams in soil: Influence of amide linkages and supramolecular structure

Polyurethane (PU) foams are classified as physically nonrecyclable thermosets. The current effort of sustainable and eco-friendly production makes it essential to explore methods of better waste management, for instance by modifying the structure of these frequently used polymers to enhance their microbial degradability. The presence of ester links is known to be a crucial prerequisite for the biodegradability of PU foams. However, the impact of other hydrolysable groups (urethane, urea and amide) occurred in PU materials, as well as the supramolecular structure of the PU network and the cellular morphology of PU foams, is still relatively unexplored. In this work, fully aliphatic PU foams with and without hydrolyzable amide linkages were prepared and their aerobic biodegradation was investigated using a six-month soil burial test. Besides the variable chemical composition of the PU foams, the influence of their different supramolecular arrangement and cellular morphologies on the extent of biodegradation was also evaluated. Throughout the soil burial test, the release of carbon dioxide, and enzyme activities of proteases, esterases, and ureases were measured. At the same time, phospho-lipid fatty acids (PLFA) analysis was conducted together with an assessment of microbial community composition achieved by analysing the genetic information from the 16S rRNA gene and ITS2 region sequencing. The results revealed a mineralization rate of 30-50 % for the PU foams, indicating a significant level of degradation as well as indicating that PU foams can be utilized by soil microorganisms as a source of both energy and nutrients. Importantly, microbial biomass remained unaffected, suggesting that there was no toxicity associated with the degradation products of the PU foams. It was further confirmed that ester linkages in PU foam structure were easily enzymatically cleavable, while amide linkages were not prone to degradation by soil microorganisms. In addition, it was shown that the presence of amide linkages in PU foam leads to a change in the supramolecular network arrangement due to increased content of hard segments, which in turn reduces the biodegradability of PU foam. These findings show that it is important to consider both chemical composition and supramolecular/macroscopic structure when designing new PU materials in an effort to develop environmentally friendly alternatives.

Compost, plants and endophytes versus metal contamination: choice of a restoration strategy steers the microbiome in polymetallic mine waste

Finding solutions for the remediation and restoration of abandoned mining areas is of great environmental importance as they pose a risk to ecosystem health. In this study, our aim was to determine how remediation strategies with (i) compost amendment, (ii) planting a metal-tolerant grass Bouteloua curtipendula, and (iii) its inoculation with beneficial endophytes influenced the microbiome of metal-contaminated tailings originating from the abandoned Blue Nose Mine, SE Arizona, near Patagonia (USA). We conducted an indoor microcosm experiment followed by a metataxonomic analysis of the mine tailings, compost, and root samples. Our results showed that each remediation strategy promoted a distinct pattern of microbial community structure in the mine tailings, which correlated with changes in their chemical properties. The combination of compost amendment and endophyte inoculation led to the highest prokaryotic diversity and total nitrogen and organic carbon, but also induced shifts in microbial community structure that significantly correlated with an enhanced potential for mobilization of Cu and Sb. Our findings show that soil health metrics (total nitrogen, organic carbon and pH) improved, and microbial community changed, due to organic matter input and endophyte inoculation, which enhanced metal leaching from the mine waste and potentially increased environmental risks posed by Cu and Sb. We further emphasize that because the initial choice of remediation strategy can significantly impact trace element mobility via modulation of both soil chemistry and microbial communities, site specific, bench-scale preliminary tests, as reported here, can help determine the potential risk of a chosen strategy.

Development of methods based on low-temperature partitioning (LTP) for monitoring cresols and chlorophenols in sewage sludge, soil, and water in column leaching

Cresols and chlorophenols are chemical contaminants that are potentially toxic to humans and can be found in sewage sludge. These chemical contaminants can migrate into the sludge-soil-water system when sludge is used as a conditioner for agricultural soils. Thus, the objective of this study was to develop methodologies based on extraction with low-temperature partitioning (LTP) to determine cresols and chlorophenols in sewage sludge, soil, and water. The analysis was performed by gas chromatography coupled with mass spectrometry (GC-MS). The validated methods were applied to monitor cresols and chlorophenols in a column-leaching study of a sludge-soil-water system. Satisfactory results were achieved for selectivity, limit of quantification (LOQ), linearity, accuracy, and precision. In the column leaching study, only 2,4,6-trichlorophenol was quantified in sludge samples after 20 days of the experiment. None of the studied compounds were quantified in soil and leached water samples, due to the degradation promoted by the microorganisms present in the sewage sludge. Finally, validated methods were suitable for monitoring cresols and chlorophenols in the sludge-soil-water system.

Legacy Effects of Phytoremediation on Plant-Associated Prokaryotic Communities in Remediated Subarctic Soil Historically Contaminated with Petroleum Hydrocarbons

Phytoremediation of petroleum hydrocarbons in subarctic regions relies on the successful establishment of plants that stimulate petroleum-degrading microorganisms, which can be challenging due to the extreme climate, limited nutrients, and difficulties in maintaining sites in remote locations. A long-term phytoremediation experiment was initiated in Alaska in 1995 with the introduction of grasses and/or fertilizer to petroleum hydrocarbon (PHC)-contaminated soils that were subsequently left unmanaged. In 2011, the PHC concentrations were below detection limits in all soils tested and the originally planted grasses had been replaced by volunteer plant species that had colonized the site. Here, we sought to understand how the original treatments influenced the structure of prokaryotic communities associated with plant species that colonized the soils and to assess the interactions between the rhizospheric and endophytic communities of the colonizing vegetation 20 years after the experiment was established. Metataxonomic analysis performed using 16S rRNA gene sequencing revealed that the original type of contaminated soil and phytoremediation strategy influenced the structure of both rhizospheric and endophytic communities of colonizing plants, even 20 years after the treatments were applied and following the disappearance of the originally planted grasses. Our findings demonstrate that the choice of initial phytoremediation strategy drove the succession of microorganisms associated with the colonizing vegetation. The outcome of this study provides new insight into the establishment of plant-associated microbial communities during secondary succession of subarctic areas previously contaminated by PHCs and indicates that the strategies for restoring these ecosystems influence the plant-associated microbiota in the long term. IMPORTANCE Subarctic ecosystems provide key services to local communities, yet they are threatened by pollution caused by spills and disposal of petroleum waste. Finding solutions for the remediation and restoration of subarctic soils is valuable for reasons related to human and ecosystem health, as well as environmental justice. This study provides novel insight into the long-term succession of soil and plant-associated microbiota in subarctic soils that had been historically contaminated with different sources of PHCs and subjected to distinct phytoremediation strategies. We provide evidence that even after the successful removal of PHCs and the occurrence of secondary succession, the fingerprint of the original source of contamination and the initial choice of remediation strategy can be detected as a microbial legacy in the rhizosphere, roots, and shoots of volunteer vegetation even 2 decades after the contamination had occurred. Such information needs to be borne in mind when designing and applying restoration approaches for PHC-contaminated soils in subarctic ecosystems.

Soil microbial communities following 20 years of fertilization and crop rotation practices in the Czech Republic

BACKGROUND

Although fertilization and crop rotation practices are commonly used worldwide in agriculture to maximize crop yields, their long-term effect on the structures of soil microorganisms is still poorly understood. This study investigated the long-term impact of fertilization and crop rotation on soil microbial diversity and the microbial community structure in four different locations with three soil types. Since 1996, manure (MF; 330 kg N/ha), sewage sludge (SF; 330 and SF3x; 990 kg N/ha), and NPK (NPK; 330 kg N/ha) fertilizers were periodically applied to the soils classified as chernozem, luvisol and cambisol, which are among the most abundant or fertile soils used for agricultural purposes in the world. In these soils, potato (Solanum tuberosum L.), winter wheat (Triticum aestivum L.), and spring barley (Hordeum vulgare L.) were rotated every three years.

RESULTS

Soil chemistry, which was significantly associated with location, fertilization, crop rotation, and the interaction of fertilization and location, was the dominant driver of soil microbial communities, both prokaryotic and fungal. A direct effect of long-term crop rotation and fertilization on the structure of their communities was confirmed, although there was no evidence of their influence on microbial diversity. Fungal and bacterial communities responded differently to fertilization treatments; prokaryotic communities were only significantly different from the control soil (CF) in soils treated with MF and SF3x, while fungal communities differed across all treatments. Indicator genera were identified for different treatments. These taxa were either specific for their decomposition activities or fungal plant pathogens. Sequential rotation of the three crops restricted the growth of several of the indicator plant pathogens.

CONCLUSIONS

Long-term fertilization and crop rotation significantly altered microbial community structure in the soil. While fertilization affected soil microorganisms mainly through changes in nutrient profile, crop rotations lead to the attraction and repulsion of specific plant pathogens. Such changes in soil microbial communities need to be considered when planning soil management.

Response of 2,4,6-trichlorophenol-reducing biocathode to burial depth in constructed wetland sediments

Biocathode systems could be used for in-situ bioremediation of chlorophenols (CPs) in constructed wetland (CW) sediments. However, little is known regarding whether or how cathode burial depths affect the dechlorination of CPs in sediments. Here, 2,4,6-trichlorophenol (2,4,6-TCP)-dechlorinating biocathode systems were constructed under a cathode potential of - 0.7 V (vs. a saturated calomel electrode, SCE) at three different cathode burial depths (5, 10, and 15 cm). The 2,4,6-TCP removal efficiency and average transformation rate with the biocathode increased by 21.46-36.86% and 14.63-34.88% compared to those in the non-electrode groups. Deeper cathode burial depths enhanced the 2,4,6-TCP dechlorination performance. Furthermore, the oxidation-reduction potential (ORP) of the sediment decreased with sediment depth and the applied potential created a more favorable redox environment for the enrichment of functional bacteria. Deeper cathode burial depths also promoted the selective enrichment of electro-active and dechlorinating bacteria (e.g., Bacillus and Dehalobacter, respectively). The biocathode thus served as the carrier, electron source, and regulator of functional bacteria to accelerate the transformation of 2,4,6-TCP (2,4,6-TCP → 2,4-dichlorophenol → 4-chlorophenol → phenol) in sediments. These results offer insights into the effects of cathode burial depth on 2,4,6-TCP dechlorination in sediments from a redox environment and microbial community structure standpoint.

Reduction-oxidation series coupling degradation of chlorophenols in Pd-Catalytic Electro-Fenton system

Organochlorine pesticides are widespread in soils, sediments and even in groundwater, causing great concern to human health because of its toxicity and carcinogenic effects. The remarkable mineralization and lowered toxicity are particularly important during the removal of organochlorine pesticides. In this study, Pd/CeO₂ was prepared and employed as a bifunctional catalyst, to construct the reduction-oxidation series coupling Electro-Fenton (EF) system. The removal of chlorophenols (CPs) reached over 95% within 10 min at pH 3.0 and a current density of 25 mA/cm² in Pd/CeO₂-EF system. The second-order rate constant of CPs degradation was 10.28 L mmol^-1min^-1 in Pd/CeO₂-EF system, which was 29 times as fast as the sum of electrolysis with Pd/CeO₂ (0.24 L mmol^-1min^-1) and EF (0.11 L mmol^-1min^-1). Dehydrochlorination by Pd [H] contributed to the removal of CPs in Pd/CeO₂-EF system. The generated reactive oxygen species, mainly OH was also confirmed by ESR to contribute to the removal of CPs. The reduction-oxidation series coupling degradation of CPs in Pd/CeO₂-EF system increased the TOC removal to 70% in 360 min. The analysis of intermediate products further revealed the reductive and oxidative products in Pd/CeO₂-EF. Moreover, the system of Pd/CeO₂-EF exhibited an excellent performance treatment for CPs in actual groundwater. This study provides a new stratagem to eliminate organochlorine pesticides in groundwater environments rapidly and thoroughly.

Effects of salinity on pollutant removal and bacterial community in a partially saturated vertical flow constructed wetland

This study investigated the influence of salinity on pollutant removal and bacterial community within a partially saturated vertical flow constructed wetland (PS-VFCW). High removal rates of NH₄⁺-N (88.29 ± 4.97-100 ± 0%), total inorganic nitrogen (TIN) (50.00 ± 7.21-62.81 ± 7.21%) and COD (91.08 ± 2.66-100 ± 0%) were achieved at 0.4-2.4% salinity levels. The removal of ammonia, TIN and organic matter occurred mainly in unsaturated zone. Salt-adaptable microbes became the dominant bacteria with salinity elevated. The proportion of ammonia-oxidizing bacteria (AOB) in the 0-5 cm depth layer (unsaturated zone) decreased obviously as the salinity increased to 2.4%. Nitrite-oxidizing bacteria (NOB) in the 0-5 cm depth layer showed a decreasing trend with elevated salinity. Denitrifying bacteria (DNB) in the 0-5 cm depth layer maintained high abundance (27.70-53.60%) at 0.4-2.4% salinity levels. At 2.4% salinity, AOB, NOB and DNB were observed in the unsaturated zones and saturated zones, and showed higher abundance in the unsaturated zone.

Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes

Chlorophenols (CPs) are highly toxic and refractory contaminants which widely exist in various environments and cause serious harm to human and environment health and safety. This review provides comprehensive information on typical CPs biodegradation technologies, the most green and benign ones for CPs removal. The known aerobic and anaerobic degradative bacteria, functional enzymes, and metabolic pathways of CPs as well as several improving methods and critical parameters affecting the overall degradation efficiency are systematically summarized and clarified. The challenges for CPs mineralization are also discussed, mainly including the dechlorination of polychlorophenols (poly-CPs) under aerobic condition and the ring-cleavage of monochlorophenols (MCPs) under anaerobic condition. The coupling of functional materials and degraders as well as the operation of sequential anaerobic-aerobic bioreactors and bioelectrochemical system (BES) are promising strategies to overcome some current limitations. Future perspective and research gaps in this field are also proposed, including the further understanding of microbial information and the specific role of materials in CPs biodegradation, the potential application of innovative biotechnologies and new operating modes to optimize and maximize the function of the system, and the scale-up of bioreactors towards the efficient biodegradation of CPs.

Effect of chelated iron activated peroxydisulfate oxidation on perchloroethene-degrading microbial consortium

In this work, the effect of In-Situ Chemical Oxidation (ISCO) using peroxydisulfate (PDS) on chloroethenes-degrading microbial consortium in the presence of perchloroethene (PCE; tetrachloroethene) was investigated. Degradation of PCE was examined using PDS without an activation, activated with iron Fe(II) chelated by citric acid (CA), and microbial consortium derived from chloroethenes-contaminated site in liquid and sand microcosms. Two different molar ratios of PCE/PDS/(Fe(II)+CA) (1/8/1.6 and 1/16/3.2) were tested. The PCE removal efficiency was the highest in the bacteria-free microcosms. An expected increase in the PCE removal efficiency by coupling PDS and microbial consortium was not confirmed. Surprisingly, the reduced capacity of PDS to remove PCE in the systems containing both PDS and microbial consortium was observed indicating that indigenous microbes may reduce the efficiency of PDS during a remediation. High-throughput 16S rRNA gene sequencing analysis revealed negative effect of PDS on organohalide-respiring bacteria (OHRB), which were not detected after 19 days of the experiment, unlike in biotic control. On the other hand, amplicon sequence variants (ASVs) affiliated with genera Brevundimonas and Pseudomonas that have been described for their capability of aerobic cometabolic/metabolic degradation of chloroethenes (CEs) were among the most frequently detected ASVs after the PDS treatment. Results further showed that the sole Fe(II)-CA affected the diversity of the microbial consortium. Overall, results of this study provide new insight into the coupling ISCO using PDS with in situ bioremediation of CEs.

Degradation of organic pollutants by intimately coupling photocatalytic materials with microbes: a review

With the rapid development of industry and agriculture, large amounts of organic pollutants have been released into the environment. Consequently, the degradation of refractory organic pollutants has become one of the toughest challenges in remediation. To solve this problem, intimate coupling of photocatalysis and biodegradation (ICPB) technology, which allows the simultaneous action of photocatalysis and biodegradation and thus integrates the advantages of photocatalytic reactions and biological treatments, was developed recently. ICPB consists mainly of porous carriers, photocatalysts, biofilms, and an illuminated reactor. Under illumination, photocatalysts on the surface of the carriers convert refractory pollutants into biodegradable products through photocatalytic reactions, after which these products are completely degraded by the biofilms cultivated in the carriers. Additionally, the biofilms are protected by the carriers from the harmful light and free radicals generated by the photocatalyst. Compared with traditional technologies, ICPB remarkably improves the degradation efficiency and reduces the cost of bioremediation. In this review, we introduce the origin and mechanisms of ICPB, discuss the development of reactors, carriers, photocatalysts, and biofilms used in ICPB, and summarize the applications of ICPB to treat organic pollutants. Finally, gaps in this research as well as future perspectives are discussed.

Impact of electrical stimulation modes on the degradation of refractory phenolics and the analysis of microbial communities in an anaerobic-aerobic-coupled upflow bioelectrochemical reactor

An electrically stimulated anaerobic-aerobic coupled system was developed to improve the biodegradation of refractory phenolics. Expected 4-nitrophenol, 2, 4-dinitrophenol, and COD removals in the system with aerobic cathodic and anaerobic anodic chambers were approximately 53.7%, 45.4%, 22.3% (intermittent mode) and 37.9%, 19.8%, 17.3% (continuous mode) higher than that in the control system (26.0 ± 6.4%, 30.7 ± 7.1%, 49.8 ± 3.0%). 2, 4-dichlorophenol removal in the system with aerobic anodic and anaerobic cathodic chambers was approximately 28.5% higher than that in the control system (71.4 ± 5.7%). The contribution of the aerobic cathodic/anodic chambers to the removal of phenolic compounds was higher than that of the anaerobic cathodic/anodic chambers. The species related to phenolic biodegradation (Rhodococcus, Achromobacter, PSB-M-3, and Sphingobium) were enriched in the cathodic and anodic chambers of the system. These results showed that intermittent electrical stimulation could be a potential alternative for the efficient degradation of refractory phenolics.

Microbial Communities in Soils and Endosphere of Solanum tuberosum L. and their Response to Long-Term Fertilization

An understanding of how fertilization influences endophytes is crucial for sustainable agriculture, since the manipulation of the plant microbiome could affect plant fitness and productivity. This study was focused on the response of microbial communities in the soil and tubers to the regular application of manure (MF; 330 kg N/ha), sewage sludge (SF; 330 and SF3x; 990 kg N/ha), and chemical fertilizer (NPK; 330-90-300 kg N-P-K/ha). Unfertilized soil was used as a control (CF), and the experiment was set up at two distinct sites. All fertilization treatments significantly altered the prokaryotic and fungal communities in soil, whereas the influence of fertilization on the community of endophytes differed for each site. At the site with cambisol, prokaryotic and fungal endophytes were significantly shifted by MF and SF3 treatments. At the site with chernozem, neither the prokaryotic nor fungal endophytic communities were significantly associated with fertilization treatments. Fertilization significantly increased the relative abundance of the plant-beneficial bacteria Stenotrophomonas, Sphingomonas and the arbuscular mycorrhizal fungi. In tubers, the relative abundance of Fusarium was lower in MF-treated soil compared to CF. Although fertilization treatments clearly influenced the soil and endophytic community structure, we did not find any indication of human pathogens being transmitted into tubers via organic fertilizers.

Long-term alkaline conditions inhibit the relative abundances of tetracycline resistance genes in saline 4-chlorophenol wastewater treatment

Considering the occurrence and spread of antibiotic resistance genes (ARGs) pose significant risks to public health, the effects of long-term exposure to alkaline conditions on the relative abundances of tetracycline resistance genes (TRGs) were studied in saline 4-chlorophenol (4-CP) wastewater treatment. Alkaline conditions were maintained by supplying the co-metabolic carbon source of sodium acetate. Results showed that except for the 4-CP, the removal of pollutants was significantly inhibited, and the relative abundances of the most TRGs were repressed. In addition, the removal of pollutants and the relative abundances of TRGs were moderately affected by the NaCl addition. The proteins in the extracellular polymeric substances (EPS) played key roles in reducing the relative abundances of TRGs, which were altered by the microbial diversity. In conclusion, for the pollutants removal and ARGs reduction in refractory industrial wastewater treatment, alkaline conditions should be maintained by selecting suitable co-metabolic carbon sources.

Bacterial succession in oil-contaminated soil under phytoremediation with poplars

Petroleum hydrocarbons (PHCs) continue to be among the most common pollutants in soil worldwide. Phytoremediation has become a sustainable way of dealing with PHC contamination. We conducted the off-site phytoremediation of PHC-polluted soil from an oil tanker truck accident, where poplars were used for the phytoremediation of the oil-polluted soil in a boreal climate during a seven-year treatment. The succession of bacterial communities over the entire phytoremediation process was monitored using microbial ecological tools relying on high-throughput 16S rRNA gene sequencing. Upon the successful depletion of PHCs from soil, endophytic communities were analyzed in order to assess the complete plant-associated microbiome after the ecological recovery. The rhizosphere-associated soil exhibited different bacterial dynamics than unplanted soil, but both soils experienced succession of bacteria over time, with diversity being negatively correlated with PHC concentration. In the relatively short growing season in North Europe, seasonal variations in environmental conditions were identified that contributed to the dynamics of bacterial communities. Overall, our study proved that phytoremediation using poplar trees can be used to assist in the removal of PHCs from soils in boreal climate conditions and provides new insight into the succession patterns of bacterial communities associated with these plants.