Investigations of microbial degradation of polycyclic aromatic hydrocarbons based on 13C-labeled phenanthrene in a soil co-contaminated with trace elements using a plant assisted approach

Improved microbial-plant soil bioremediation of PAHs and heavy metal through in silico methods

The combined pollution of polycyclic aromatic hydrocarbons (PAHs) and organic cadmium (Cd) in farmland soils, and the field controlling strategy need to be studied urgently. In this study, 5 PAHs, 5 Cd and 11 soil conditioners were selected to explore the co-exposure risk and remediation efficiency. Firstly, a significant combination Fl-alkylalkoxy cadmium was obtained using forward and reverse methods coupling variation coefficient methods (the combined pollution value was 0.173). Secondly, the interaction energy of microbial degradation / plant absorption of Fl under Cd stress, and microbial mineralization / plant absorption of alkylalkoxy cadmium under PAHs stress were characterized using factorial experimental design, molecular docking and molecular dynamics simulation. The combined pollution of alkylalkoxy cadmium and dialkyl cadmium, phenanthrene and Benzo [a] pyrene was significant (synergistic contribution rates were 17.58 % and 19.22 %, respectively). In addition, 6 soil conditioners with significant efficiency were selected to design Taguchi orthogonal experimental schemes, indicating the microbial degradation / mineralization and plant absorption were significantly effective (the maximum increase of remediation efficiency was 93.81 %) under the combinations (i.e., trratone, coumarol, fulvamic acid, potassium fertilizer and others, etc.). Finally, it was found that the soil conditioners affected the hydrophobic groups and forces, and the efficiency was proportional to the highest peak value and minimum distance in the RDF curve. This study identifies the risk characteristics of co-exposure of PAHs and Cd and screens effective soil conditioners, providing theoretical guidance for risk controlling.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

Characteristics of organic pollutants and their effects on the microbial composition and activity in the industrial soils of Pearl River Delta, China

To investigate the interaction between organic pollutants and soil microorganisms, industrial soils were collected from Pearl River Delta region of China for determining semi-volatile organic pollutants, the community structure and activity of microorganisms. The results showed that polycyclic aromatic hydrocarbons (PAHs) (63.3-4956 μg kg^-1) and phthalate esters (PAEs) (272-65,837 μg kg^-1) were main organic pollutants in the research area soils. Chemical manufacturing industry and plastics manufacturing industry contributed greatly to PAH pollution and PAE pollution, respectively. Organic pollutants changed the biomass of microorganisms. In most industrial soils, the biomass of actinomycetes was the highest in the industrial soils, followed by G^- bacteria, G⁺ bacteria and fungi. The exception was that the biomass of fungi in the soil near chemical manufacturing industry was greater than that of G⁺ bacteria. The soil microbial biomass (including soil microbial biomass carbon, soil microbial biomass nitrogen, the biomass of actinomycetes, bacteria, and fungi) and soil enzyme activities (sucrase and urease) positively correlated with the organic pollutant residues, and the microbial species diversity and microbial species abundance decreased with organic pollutant residues increasing. Based on the correlation analysis, the urease activity, actinomycetes biomass, and fungi biomass were appropriate biological indicators for evaluating the stress of organic pollutants. Our research provides a new perspective for understanding the soil biological response in industrial soils.

Different phenanthrene degraders between free-cell mediated and biochar-immobilization assisted soil bioaugmentation as identified by RNA-based stable isotope probing (RNA-SIP)

Bioaugmentation (BA) is an effective approach to remove polycyclic aromatic hydrocarbons (PAHs) from contaminated soils, and biochar is frequently used to enhance PAH degradation performance. In this study, phenanthrene (PHE) degradation behavior and active degraders in a petroleum-contaminated soil were investigated and compared between free-cell mediated and biochar-immobilization assisted bioaugmentation. Biochar-immobilization assisted bioaugmentation (BA-IPB) introduced PHE degraders immobilized on biochar and effectively promoted PHE degradation, achieving higher PHE removal efficiencies within 24 h (~58 %) than free-cell mediated bioaugmentation (BA-FPB, ~39 %). Soil microbial community structure significantly changed in both BA-FPB and BA-IPB treatments. Through RNA-stable isotope probing (SIP), 14 and 11 bacterial lineages responsible for in situ PHE degradation were identified in BA-FPB and BA-IPB treatments, respectively. ASV_17 in BA-FPB treatment was Rhodococcus in the exogenous bacterial mixture; in contrast, none of exogenous bacteria were involved in PHE degradation in BA-IPB treatment. Methylobacterium (ASV_186), Xanthomonas (ASV_41), Kroppenstedtia (ASV_205), Scopulibacillus (ASV_243), Bautia (ASV_356), and Lactobacillus (ASV_376) were identified as PHE degraders for the first time. Our findings expanded the knowledge of the active PHE degraders and underlying mechanisms in bioaugmentation process, and suggested biochar-immobilization assisted bioaugmentation as a promising strategy for the bioremediation of PAH contaminated soils.

Acute effects of PAH contamination on microbial community of different forest soils

Polycyclic aromatic hydrocarbons (PAHs) are hazardous organic compounds with mutagenic, genotoxic and carcinogenic properties. Although PAHs in soil can cause toxicity to microorganisms, the microbial community is able to degrade these compounds. For this reason, it is important to study acute and short-term effects of PAH contamination on soil microbial community, also to shed light on its possible exploitation in soil restoration. The effects of acute PAH contamination on the structure and metabolic activity of microbial communities in three forest (beech, holm oak, black pine) soils were studied. The soils were spiked with phenanthrene, pyrene or benzo[a]pyrene and incubated in experimental mesocosms, under controlled conditions. Enzymatic activities (laccase, total peroxidase and hydrolase), as well as microbial biomass and community structure (through phospholipid fatty acid and ergosterol analyses), were evaluated in the three soil systems 4 days after contamination and compared to no-spiked soils. In soil under holm oak, there was a stimulation of Gram+ bacteria after contamination with all the 3 PAHs, whereas in soil under pine, pyrene and phenanthrene additions mainly stimulated fungi and actinomycetes.

Role of different microorganisms in remediating PAH-contaminated soils treated with compost or fungi

Microbial degradation is the main responsible for polycyclic aromatic hydrocarbons (PAHs) removal from contaminated soils, and the understanding of this process is pivotal to define effective bioremediation approaches. To evaluate the contribution of several microbial groups in soil anthracene and benzo[a]pyrene degradation, the analysis of phospholipid fatty acid (PLFA) profiles and machine learning techniques were employed. To this end, PLFAs and PAH concentrations were analysed, along 274 days of incubation in mesocosms, in soils artificially contaminated with anthracene and benzo[a]pyrene, subjected to different treatments: untreated soil and soils treated with biowaste compost or fungal consortium. Random forest models, figuring anthracene or benzo[a]pyrene concentrations as dependent variables and PLFAs as predictors, were then built to evaluate the contribution of each variable in PAH degradation. PLFA profiles varied substantially among soil treatments and along time, with the increase of Actinomycetes in soils added with fungi and other Gram+ bacteria in compost amended soils. The former, together with fungi, are primarily responsible for anthracene and benzo[a]pyrene degradation in both treated soils, a process in which also metanotrophs and other Gram+ and Gram- bacteria participate. In untreated soil, the cooperation of a multitude of different microorganisms was, instead, responsible for PAH removal, a process with lower efficiency in respect to treated soils.

Anaerobic digestion

Worldwide waste generation has become a topic of interest since the accumulation of this waste has prompted environmental hazards. Among which, anaerobic digestion provides green and efficient alternate solution for removal of toxic waste and energy production. Therefore, this review emphasizes on the recent data published in 2018 on topics related to anaerobic process, enhancement of biogas production, and fermentation efficiency. Furthermore, more focus was made on the factors influencing anaerobic digestion and the effect of trace elements as ionic salts as well as nanoparticles on overall biogas production, respectively. PRACTITIONER POINTS: Anaerobic digestion provide green and efficient alternate solution to deal with. This review focused on the conditions related to anaerobic process to improve biogas production and fermentation efficiency. The trace elements were focused on how to influence biogas production during anaerobic digestion.

Catalytic Pyrolysis of Biomass and Polymer Wastes

Oil produced by the pyrolysis of biomass and co-pyrolysis of biomass with waste synthetic polymers has significant potential as a substitute for fossil fuels. However, the relatively poor properties found in pyrolysis oil—such as high oxygen content, low caloric value, and physicochemical instability—hampers its practical utilization as a commercial petroleum fuel replacement or additive. This review focuses on pyrolysis catalyst design, impact of using real waste feedstocks, catalyst deactivation and regeneration, and optimization of product distributions to support the production of high value-added products. Co-pyrolysis of two or more feedstock materials is shown to increase oil yield, caloric value, and aromatic hydrocarbon content. In addition, the co-pyrolysis of biomass and polymer waste can contribute to a reduction in production costs, expand waste disposal options, and reduce environmental impacts. Several promising options for catalytic pyrolysis to become industrially viable are also discussed.

Benefits and limitations of biochar amendment in agricultural soils: A review

Current agriculture faces multiple challenges due to rapid increases in food demand and environmental concerns. Recently, biochar application in agricultural soils has attracted a good deal of attention. According to literature findings, biochar has proven to play various beneficial roles with respect to the enhancement of crop yield as a fertilizer and soil quality as a soil conditioner. It can further be used to remediate soil pollution as an adsorbent, while supporting the mitigation of greenhouse gases (GHGs) through the expansion of the soil carbon pool. The efficacy of biochar application on agricultural environments is found to be controlled by various factors such as pyrolysis temperature, feed stock, soil type, and biotic interactions. The combined effects of these factors may thus exert a decisive control on the overall outcome. Furthermore, the biochar application can also be proven to be detrimental in some scenarios. This review evaluates both the potential benefits and limitations of biochar application in agriculture soils.