Combined Effects of Plant Cultivation and Sorbing Carbon Amendments on Freely Dissolved PAHs in Contaminated Soil

Biochar alters the persistence of PAHs in soils by affecting soil physicochemical properties and microbial diversity: A meta-analysis

Polycyclic aromatic hydrocarbons (PAHs) pollution in soil is a pervasive environmental issue worldwide. Although biochar has the potential to immobilize PAHs in soils, there remains a study gap in the use of systematic analyses to assess the effectiveness of biochar for PAH removal and the factors that affect biochar. Hence, a meta-analysis utilizing 56 published studies was aimed to assess the impact of biochar on the PAH content, soil physicochemical properties, and microbial diversity in PAH-contaminated soils and to elucidate what factors impact the capability of biochar to alter PAH persistence. With biochar application, soil Ctot PAH concentrations were significantly reduced (15.4%), while the levels of Cfree PAHs and Cbioacc PAHs were reduced by 55.6% and 46.5%, respectively. Additionally, biochar improved the physicochemical properties of PAH-contaminated soil and increased the diversity of microorganisms. Particularly, the relative abundance of PAH degraders increased significantly (43.7%), which indicated that PAH biodegradation was significantly enhanced. Soil physicochemical properties and biochar production conditions are indispensable for the study of the PAH persistence. The overall findings revealed that the pyrolysis of woody biochar at 300-500 °C was beneficial for reducing the PAH persistence in acidic, coarse, or fine and high soil organic matter content (>20 g/kg) soils.

Phytoremediation of crude oil-contaminated sediment using Suaeda heteroptera enhanced by Nereis succinea and oil-degrading bacteria

A 150-day experiment was performed to investigate the stimulatory effect of a promising phytoremediation strategy consisting of Suaeda heteroptera (S. heteroptera), Nereis succinea (N. succinea), and oil-degrading bacteria for cleaning up total petroleum hydrocarbons (TPHs) in spiked sediment. Inoculation with oil-degrading bacteria and/or N. succinea increased plant yield and TPH accumulation in S. heteroptera plants. The highest TPH dissipation (40.5%) was obtained in the combination treatment, i.e., S. heteroptera + oil-degrading bacteria + N. succinea, in which the sediment TPH concentration decreased from an initial value of 3955 to 2355 mg/kg in 150 days. BAF, BCF, and TF confirmed the role of N. succinea and oil-degrading bacteria in the amelioration and translocation of TPHs. In addition, TPH toxicity of S. heteroptera was alleviated by N. succinea and oil-degrading bacteria addition through the reduction of oxidative stress. Therefore, S. heteroptera could be used for cleaning up oil-contaminated sediment, particularly in the presence of oil-degrading bacteria + N. succinea. Field studies on oil-degrading bacteria + N. succinea may provide new insights on the rehabilitation and restoration of sediments contaminated by TPHs.

Biochar application strategies for polycyclic aromatic hydrocarbons removal from soils

Polycyclic aromatic hydrocarbons (PAHs) are known as a hazardous group of pollutants in the soil which causes many challenges to the environment. In this study, the potential of biochar (BC), as a carbonaceous material, is evaluated for the immobilization of PAHs in soils. For this purpose, various bonding mechanisms of BC and PAHs, and the strength of bonds are firstly described. Also, the effect of impressive criteria including BC physicochemical properties (such as surface area, porosity, particle size, polarity, aromaticity, functional group, etc., which are mostly the function of pyrolysis temperature), number of rings in PAHs, incubation time, and soil properties, on the extent and rate of PAHs immobilization by BC are explained. Then, the utilization of BC in collaboration with biological tools which simplifies further dissipation of PAHs in the soil is described considering detailed interactions among BC, microbes, and plants in the soil matrix. The co-effect of BC and biological remediation has been authenticated by previous studies. Moreover, recent technologies and challenges related to the application of BC in soil remediation are explained. The implementation of a combined BC-biological remediation method would provide excellent prospects for PAHs-contaminated soils.

Response of Rhizosphere Microbial Community in High-PAH-Contaminated Soil Using Echinacea purpurea (L.) Moench

Under polycyclic aromatic hydrocarbon (PAH) pollution conditions (149.17–187.54 mg/kg), we had found the dominant flora of PAHs by observing the response of the soil microbial community after planting purple coneflower (Echinacea purpurea (L.) Moench). In this study, pot experiments were conducted in a growth chamber to explore the changes in the rhizosphere microbial community structure during remediation of heavily PAH-contaminated soil using purple coneflower (Echinacea purpurea (L.) Moench). The phospholipid fatty acid (PLFA) content in the soil was measured during four periods before and after planting, and the results showed that: (i) at 120 days, E. purpurea can regulate the microbial community structure but had no significant effect on soil microbial diversity, (ii) at 120 days, the number of PLFAs characterizing actinomycetes, bacteria, and fungi increased, and both Gram-negative bacteria and Arbuscular mycorrhizal fungi (AMF) were significant with the observed PLFA level (p < 0.05), and (iii) the results indicated that AMF and Gram-negative bacteria represent some of the main factors that can promote the degradation of PAHs. The results obtained in this work are important to future research on PAH-degradation-functional genes and degradation mechanisms of the selection of flora.

Bioengineered biochar as smart candidate for resource recovery toward circular bio-economy: a review

Biochar's ability to mediate and facilitate microbial contamination degradation, as well as its carbon-sequestration potential, has sparked interest in recent years. The scope, possible advantages (economic and environmental), and future views are all evaluated in this review. We go over the many designed processes that are taking place and show why it is critical to look into biochar production for resource recovery and the role of bioengineered biochar in waste recycling. We concentrate on current breakthroughs in the fields of engineered biochar application techniques to systematically and sustainable technology. As a result, this paper describes the use of biomass for biochar production using various methods, as well as its use as an effective inclusion material to increase performance. The impact of biochar amendments on microbial colonisation, direct interspecies electron transfer, organic load minimization, and buffering maintenance is explored in detail. The majority of organic and inorganic (heavy metals) contaminants in the environment today are caused by human activities, such as mining and the use of chemical fertilizers and pesticides, which can be treated sustainably by using engineered biochar to promote the establishment of a sustainable engineered process by inducing the circular bioeconomy.

Recent advances in biochar engineering for soil contaminated with complex chemical mixtures: Remediation strategies and future perspectives

Heavy metal/metalloids (HMs) and polycyclic aromatic hydrocarbons (PAHs) in soil have caused serious environmental problems, compromised agriculture quality, and have detrimental effects on all forms of life including humans. There is a need to develop appropriate and effective remediation methods to resolve combined contaminated problems. Although conventional technologies exist to tackle contaminated soils, application of biochar as an effective renewable adsorbent for enhanced bioremediation is considered by many scientific researchers as a promising strategy to mitigate HM/PAH co-contaminated soils. This review aims to: (i) provide an overview of biochar preparation and its application, and (ii) critically discuss and examine the prospects of (bio)engineered biochar for enhancing HMs/PAHs co-remediation efficacy by reducing their mobility and bioavailability. The adsorption effectiveness of a biochar largely depends on the type of biomass material, carbonisation method and pyrolysis conditions. Biochar induced soil immobilise and remove metal ions via various mechanisms including electrostatic attractions, ion exchange, complexation and precipitation. PAHs remediation mechanisms are achieved via pore filling, hydrophobic effect, electrostatic attraction, hydrogen bond and partitioning. During last decade, biochar engineering (modification) via biological and chemical approaches to enhance contaminant removal efficiency has garnered greater interests. Hence, the development and application of (bio)engineered biochars in risk management, contaminant management associated with HM/PAH co-contaminated soil. In terms of (bio)engineered biochar, we review the prospects of amalgamating biochar with hydrogel, digestate and bioaugmentation to produce biochar composites.

Negative role of biochars in the dissipation and vegetable uptake of polycyclic aromatic hydrocarbons (PAHs) in an agricultural soil: Cautions for application of biochars to remediate PAHs-contaminated soil

Biochars were studied for their impacts on the dissipation and vegetable uptake of polycyclic aromatic hydrocarbons (PAHs) in an agricultural soil. The health risks of PAHs taken up by vegetables were assessed by growing Chinese cabbage in both unamended soil and biochar-amended soils. In the unamended soil, the total 16 PAHs (Σ16PAHs) content decreased by 77.38% after planting the vegetable. The dissipation percentages of low-molecular-weight PAHs (LMW-PAHs), medium-molecular-weight PAHs (MMW-PAHs), and high-molecular-weight PAHs (HMW-PAHs) were 82.37%, 72.65%, and 68.63%, respectively. A significant negative correlation was determined between the dissipation percentages of PAHs in soil and the logK_ow of PAHs (p < 0.01), indicating that the affinity of PAHs for soil particles was one of an important limiting factors on the dissipation of PAHs. The uptake of PAHs by plant was significantly reduced with the increase in the molecular weight of the PAHs (76.55% for LWM-PAHs, 17.13% for MMW-PAHs, and 6.05% for HMW-PAHs). Addition of biochars to the soil decreased the dissipation of Σ16PAHs (73.59-77.01%), mostly due to a decrease in the dissipation of LMW-PAHs and MMW-PAHs. This finding was due to the immobilization of LMW-PAHs and MMW-PAHs within the biochar micropores. A marked reduction of Proteobacteria in biochar-amended soils also resulted in the decreased biodegradation of PAHs. Four of six biochars significantly increased the concentrations of Σ16PAHs in plant by 30.10-74.22%. Generally, biochars significantly increased the uptake of LMW-PAHs by plant but had little influence on the plant uptake of MMW-PAHs and HMW-PAHs. Three of six biochars notably increased the incremental lifetime cancer risk values based on the exposure of PAHs by vegetable consumption.

Rapid formation of pyrogenic char (biochar) with high and low sorption capacity towards organic chemicals

Pyrogenic char (biochar) with a high sorption capacity (B-HSC) can sequester hazardous chemicals (e.g., phenanthrene). However, when sorption inhibits bioavailability of some functional chemicals (e.g., the herbicidal efficacy of diuron in soil), biochar with a low sorption capacity (B-LSC) is required to prevent sorption effects. The pyrolytic B-HSC generation has been reported, but information on B-LSC formation is scarce. How fast B-HSC and B-LSC could be generated is unknown until now. Here, biochars were rapidly prepared (the shortest heating time reached 5 min and the cooling time reached < 30 min) by a direct-pyrolysis method by directly exposing packaged rice straw and pine wood to 350 °C, 500 °C and 700 °C and out-of-furnace cooling at room temperature. The sorption of diuron, phenanthrene, and twelve other chemicals was investigated. B-HSCs were obtained within 30 min of rice straw pyrolysis, and the biochar Kd values quickly increased to 7-730-fold that of the raw biomass as -OH and C-O-C in (hemi)cellulose of rice straw rapidly degraded, increasing hydrophobic interactions between the char and chemicals (solubility ≤ 82.8 g/L). In contrast, B-LSCs were generated within 30 min of PW pyrolysis, and the Kd values of the biochars were 0.2-3.0-fold that of the raw biomass, as the surface area development and hydrophobicity-driven sorption were probably delayed by the late degradation of lignin aromatic C-O and phenolic -OH. Biochar amendment revealed an enhancement effect of B-HSC but not of B-LSC on soil sorption. The fast formation of B-LSC and B-HSC provides a guide to develop time- and cost-effective technique in pyrolytically producing weakly or strongly sorbing biochars for organic chemical management.

Long-term willows phytoremediation treatment of soil contaminated by fly ash polycyclic aromatic hydrocarbons from straw combustion

A three-year experiment was conducted to investigate willows of Salix × smithiana Willd. (S. smithiana) phytoremediation of soil contaminated by polycyclic aromatic hydrocarbons (PAHs) derived by fly ash from biomass combustion. The total removal of ash PAHs in phytoremediation treatment was 50.9% after three consecutive years while the ash PAHs were decreased in natural attenuated soil by 9.9% in the end of the experiment. The ash and spiked PAHs with low and medium molecular weight were susceptible to be removed in higher rates than high molecular weight PAHs. Lower bioconcentration factors of individual PAHs were observed in willow shoots than in roots. The estimated relative direct removal of PAHs by S. smithiana in phytoremediation was significantly lower than 1% suggesting that the contribution of S. smithiana to take up PAHs from soil was negligible and the degradation of PAHs occurred mainly in soil. Phytoremediation using S. smithiana could be seen as a feasible and environmentally friendly approach of arable soils impacted by a PAH contaminated biomass fly ash.