Activated carbon and biochar amendments decrease pore-water concentrations of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge

Degradation and mechanism of PAHs by Fe-based activated persulfate: Effect of temperature and noble metal

The accumulation of contaminants like PAHs in soil due to industrialization, urbanization, and intensified agriculture poses environmental challenges, owing to their persistence, hydrophobic nature, and toxicity. Thus, the degradation of PAHs has attracted worldwide attention in soil remediation. This study explored the effect of noble metal and temperature on the degradation of various polycyclic aromatic hydrocarbons (PAHs) in soil, as well as the types of reactive radicals generated and mechanism. The Fe-Pd/AC and Fe-Pt/AC activated persulfate exhibited high removal efficiency of 19 kinds of PAHs, about 79.95 % and 83.36 %, respectively. Fe-Pt/AC-activated persulfate exhibits superior degradation efficiency than that on Fe-Pd/AC-activated persulfate, due to the higher specific surface area and dispersity of Pt particles, thereby resulting in increased reactive radicals (·OH, SO4-· and ·OOH). Additionally, thermal activation enhances the degradation of PAHs, with initial efficiencies of 64.20 % and 55.49 % on Fe-Pd/AC- and Fe-Pt/AC-activated persulfate systems respectively, increasing to 76.05 % and 73.14 % with elevated temperatures from 21.5 to 50 °C. Metal and thermal activation facilitate S2O82- activation, generating reactive radicals, crucial for the degradation of PAHs via ring opening and oxygen hydrogenation reactions, yielding low-ring oxygen-containing derivatives such as organic acids, keto compounds, ethers, and esters. Furthermore, understanding the impact of parameters such as activation temperature and the types of noble metals on the degradation of PAHs within the activated persulfate system provides a theoretical foundation for the remediation of PAH-contaminated soil.

A Review of Remediation Strategies for Diphenyl Ether Herbicide Contamination

In agriculture, diphenyl ether herbicides are a broad-spectrum family of pesticides mainly used to control annual weeds in agriculture. Although diphenyl ether herbicides have a long-lasting effect in weed control, they can also be harmful to succeeding crops, as well as to the water and soil environment. Residual herbicides can also harm a large number of non-target organisms, leading to the death of pest predators and other beneficial organisms. Therefore, it is of great significance to control and remediate the contamination caused by diphenyl ether herbicide residues for the sake of environmental, nutritional, and biological safety. This review provides an overview of the techniques used for remediating diphenyl ether herbicide contamination, including biological, physical, and chemical remediation. Among these techniques, bioremediation, particularly microbial biodegradation technology, is extensively employed. The mechanisms and influencing factors of different remediation techniques in eliminating diphenyl ether herbicide contamination are discussed, together with a prospect for future development directions. This review serves as a scientific reference for the efficient remediation of residual contamination from diphenyl ether herbicides.

Tetracycline removal from soil by phosphate-modified biochar: Performance and bacterial community evolution

Since the remediation performance of soil tetracycline pollution by original biochar is not ideal, many modified methods have been proposed to improve its performance. Considering the cost, complex modification process and environmental friendliness, many modified biochar are difficult to be used in soil environments. In this work, biochar derived from corn stover was modified using phosphate to increase the adsorption ability of soil tetracycline and alleviate the negative effects caused by tetracycline. The results showed that pyrolysis temperatures and anion types of phosphate (PO43-, HPO42-, H2PO4-) played important roles in the performance of modified biochar. Compared with original biochar, phosphate modified biochar not only improved the adsorption capacity, but also changed the adsorption behavior of tetracycline. Via SEM, BET and FTIR techniques, the intrinsic reasons for the increase of adsorption capacity were explained by the change of morphological structures as well as functional groups of the modified biochar. K3PO4 and high temperature (800 °C) maximally improved the surface morphology, increased the pore structure, changed the surface functional groups of biochar, and then increased the adsorption capacity of tetracycline (124.51 mg/g). Subsequently, the optimal material (K3PO4-800) was selected and applied for tetracycline contaminated soil remediation. Compared to the soil without remediation, K3PO4-800 modified biochar effectively reduced the effective concentration of tetracycline in soil, and improved soil K and P nutrition, and reshaped microbial communities. Our study showed that K3PO4-800 modified biochar was not only a good tetracycline resistant material, but also a good soil amendment.

Bioavailability assessment of difenoconazole to earthworms (Eisenia fetida) in soil by oleic acid-embedded cellulose acetate membrane

Passive sampling technology is widely used to evaluate the bioavailability of pollutants. However, relatively few studies have used passive sampling membranes (PSMs) to evaluate the environmental risks of pollutants in soil, particularly pesticides. Here, the bioavailability of difenoconazole to earthworms (Eisenia fetida) was evaluated using an oleic acid-embedded cellulose acetate membrane (OECAM) for the first time. Difenoconazole reached 94 % equilibrium (T94%) within 1 d in OECAM. For soil pore water, the freely dissolved concentration (Cfree) of difenoconazole was determined using OECAM (R2 = 0.969). In the soil system, a strong linear correlation between the difenoconazole concentration in OECAM and earthworms was observed (R2 = 0.913). The bioavailability of difenoconazole was affected by the soil type and biochar content. The higher the content of soil organic matter and biochar, the lower the concentration of difenoconazole in earthworms, OECAM, and soil pore water. The concentrations of difenoconazole in pore water, earthworms, and OECAM decreased by 65.3, 42.0, and 41.6 %, respectively, when 0.5 % biochar was added. Difenoconazole mainly enters OECAM and earthworms through passive diffusion with similar uptake pathways. Therefore, the bioavailability of difenoconazole to earthworms in different soils can be evaluated using the OECAM.

Comprehensive review on lignocellulosic biomass derived biochar production, characterization, utilization and applications

Biochar is an ample source of organic carbon prepared by the thermal breakdown of biomass. Lignocellulosic biomass is a promising precursor for biochar production, and has several applications in various industries. In addition, biochar can be applied for environmental revitalization by reducing the negative impacts through intrinsic mechanisms. In addition to its environmentally friendly nature, biochar has several recyclable and inexpensive benefits. Nourishing and detoxification of the environment can be undertaken using biochar by different investigators on account of its excellent contaminant removal capacity. Studies have shown that biochar can be improved by activation to remove toxic pollutants. In general, biochar is produced by closed-loop systems; however, decentralized methods have been proven to be more efficient for increasing resource efficiency in view of circular bio-economy and lignocellulosic waste management. In the last decade, several studies have been conducted to reveal the unexplored potential and to understand the knowledge gaps in different biochar-based applications. However, there is still a crucial need for research to acquire sufficient data regarding biochar modification and management, the utilization of lignocellulosic biomass, and achieving a sustainable paradigm. The present review has been articulated to provide a summary of information on different aspects of biochar, such as production, characterization, modification for improvisation, issues, and remediation have been addressed.

Efficient pyridine biodegradation by Stenotrophomonas maltophilia J2: Degradation performance, mechanism, and immobilized application for wastewater

Stenotrophomonas maltophilia J2, a highly efficient pyridine-degrading bacterium, was isolated from the aerobic tank of a pesticide-contaminated wastewater treatment plant. The strain J2 demonstrated an impressive pyridine degradation rate of 98.34% ± 0.49% within 72 h, at a pyridine concentration of 1100 mg·L-1, a temperature of 30 °C, a pH of 8.0, and a NaCl concentration of 0.5%. Notably, two new pyridine metabolic intermediates, 1,3-dihydroxyacetone and butyric acid, were discovered, indicating that J2 may degrade pyridine through two distinct metabolic pathways. Furthermore, the immobilized strain J2 was obtained by immobilizing J2 with biochar derived from the stem of Solidago canadensis L. In the pyridine-contaminated wastewater bioremediation experiment, the immobilized strain J2 was able to remove 2000 mg·L-1 pyridine with a 98.66% ± 0.47% degradation rate in 24 h, which was significantly higher than that of the control group (3.17% ± 1.24%), and remained above 90% in subsequent cycles until the 27th cycle. High-throughput sequencing analysis indicated that the J2 +B group had an elevated relative abundance of bacteria and functional genes that could be associated with the degradation of pyridine. The results offer a foundation for the effective use of immobilized strain in the treatment of recalcitrant pyridine-contaminated wastewater.

Enhanced removal of phenanthrene and nutrients in wetland sediment with metallic biochar: Performance and mechanisms

Polycyclic aromatic hydrocarbon (PAHs) are persistent organic pollutants and pose high risk in aquatic environment. The utilization of biochar is a strategy for PAHs-contaminated remediation but is challenging due to the adsorption saturation and reoccurrence of PAHs desorbed back into water. In this study, iron (Fe) and manganese (Mn) were provided as electron acceptors for biochar modification to enhance anaerobic biodegradation of phenanthrene (Phe). Results revealed that, the Mn(Ⅳ) and Fe(Ⅲ) modification improved the removal of Phe by 24.2% and 31.4% than that of biochar, respectively. Additionally, nitrate removal was improved by 19.5% with Fe(Ⅲ) amendment. The Mn-and Fe-biochar decreased Phe contents by 8.7% and 17.4% in sediment, 10.3% and 13.8% in biochar than that of biochar. Much higher DOC contents were observed with Mn- and Fe-biochar, which provided bioavailable carbon source for microbes and contributed to microbial degradation of Phe. The greater degree of humification, higher proportions of humic and fulvic acid like components in metallic biochar participated in electron transport and further enhancing the degradation of PAHs. Microbial analysis proved the high abundance of Phe-degrading bacteria (e.g. PAH-RHD_α, Flavobacterium and Vibrio), nitrogen removal microbes (e.g. amoA, nxrA, and nir), Fe and Mn bioreduction or oxidation (e. g. Bacillus, Thermomonas, Deferribacter) with metallic biochar. Based on the results, the Fe and Mn modification, especially Fe-modified biochar provided well performance for PAHs removal in aquatic sediment.

Physicochemical properties of nanosized biochar regulated by heat treatment temperature dictates algal responses: From the perspective of fatty acid metabolism

Nanosized biochar (NBC) is an important fraction of biochar (BC) as it can exert nano-scale effects on aquatic organisms, attracting increasing research attention. However, effects of different physicochemical properties of NBC on biological responses at the metabolic and gene expression level are not comprehensively understood. Here, biological effects of NBCs pyrolyzed at different heat treatment temperatures (HTTs, 350-700 °C) were evaluated using freshwater algae Chlorella vulgaris, from the perspectives of growth and fatty acid (FA) profile changes. NBC pyrolyzed at 700 °C (N700) induced the greatest algal growth inhibition and oxidative stress than N350 and N500. In addition, NBC exposure to 50 mg/L increased saturated and monounsaturated FAs, along with a decrease in polyunsaturated FAs (PUFAs). Exposure to NBC also significantly influenced the expression of key FA metabolism genes (3fad, sad, kasi and accd), demonstrating the potential role of reactive oxygen species-mediated PUFA reduction accompanied by increased membrane permeability in algal toxicity upon NBC exposure. The observed differences in response to N700 were attributed to its smaller particle size and higher abundance of -COOH. These findings reveal the underlying mechanisms in the algal response to NBCs and provide valuable guidance for the safe design and application of BC materials.

Ecotoxicological characteristics and properties of zinc-modified biochar produced by different methods

Despite the dynamic progress of BC engineering, there is a lack of knowledge on the toxicity and environmental impact of modified BC. The aim of this study was the ecotoxicological evaluation of BC modified with zinc (Zn) using different methods: impregnation of feedstock with Zn before pyrolysis (PR), impregnation with Zn after pyrolysis (PS) and impregnation with Zn after pyrolysis with an additional calcination step (PST). The ecotoxicological assessment was based on tests with invertebrates (Folsomia candida, Daphnia magna) and bacteria (Aliivibrio fischeri). The post-treated and calcined composites had a higher content of total (C_tot) PAHs (144-276 μg kg^-1) than pre-treated BC-Zn (68-157 μg kg^-1). All BC-Zn treatments stimulated the reproduction of F. candida at the lowest BC dose (0.5%) by 4-24%. Increasing the biochar dose to 1% and 3% retained the stimulating effect of the pre-modified biochars (from 19 to 41%). Pre-modified BC-Zn reduced the luminescence of A. fischeri from 40% to 80%. Post-treated BCs reduced bacterial luminescence by 99%, but the calcination step limited the toxic effects to the level observed for the control. Post-treated BCs had a toxic effect on D. magna, with EC50 values ranging from 433 to 783 mg L^-1. The ecotoxicity of composites depends on modification methods, BC dose and pyrolysis temperature. The application of limiting conditions for HM leaching (i.e., pre-modification, calcination) increased the safety of using Zn-biochar composites.

Evaluation of the use of biochar to stabilize polycyclic aromatic hydrocarbons and phthalates in sediment

Three types of biochar (BC) (mulberry biochar (MB), wheat straw biochar, and pine tree sawdust biochar) were prepared and used to stabilize hydrophobic organic compounds (HOCs) in contaminated sediment. The kinetics of HOC adsorption to the BCs had two distinct stages. The second stage adsorption process was longer for MB than the other BCs, presumably because MB contained large pores, mesopores, and micropores. The adsorption isotherms for the three BCs were described well by the Freundlich model. The adsorption capacities of MB, WS and PT for HOCs ranged between 106.7 and 1202 μg/g, 135.1 and 1002 μg/g, and 255.6 and 909 μg/g, respectively. The apparent HOC adsorption coefficients (K_BC-w) for the three BCs were determined from the isotherm data and were similar. The HOC logK_OW values correlated well with the logK_BC-w values. In sediment slurry experiments, HOCs were much more effectively stabilized by MB than wheat straw and pine tree sawdust biochar. This was probably because of the MB pore characteristics that favored adsorption of HOCs of various molecular sizes. The Fourier-transform infrared and Raman spectra indicated that the main binding mechanisms were hydrogen boding, hydrophobic interactions, and π-π interactions. MB was found to be a possible agent for stabilizing HOCs in contaminated sediment. HOCs in sediment slurry continued to become adsorbed to MB for a long time, indicating that relatively long reaction times should be allowed for in situ remediation using MB.

Carbon nanomaterial functionalization with pesticide-detoxifying carboxylesterase

Four carbon materials, spent coffee-ground biochar, carbon black, short CNTs, and nitrogen-doped few-layer graphene (N-graphene) were tested for their functionalization with a commercial carboxylesterase. Their robustness to variations in time and key physicochemical parameters (temperature and pH) was analysed. In general, carbon nanomaterials showed better performance than biochar, both in terms of binding capacity and resilience in harsh conditions, at statistically significant levels. Among the tested materials, functionalized N-graphene also showed the highest level of inhibition of carboxylesterase by pesticide exposure. Therefore, N-graphene was selected for biotechnological application of pesticide scavenging toxicity in T. thermophila, a ciliate bioindicator of water quality. While immobilization of the enzyme was not effective in the case of carbaryl, a methyl carbamate, in the case of the organophosphorus dichlorvos, a 1- or 30-min contact time with a water solution containing 5 times the LC100 - 0.5 mM - allowed 50% and 100% rescue of ciliate survival, respectively. These results suggest that functionalization with carboxylesterase may be of additional benefit compared to bare carbon in water clean-up procedures, especially for highly hydrophilic pesticides such as dichlorvos.

Adsorption/desorption of naphthalene and phenanthrene in a binary competitive system in the riparian zone

Polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap) and phenanthrene (Phe) are organic pollutants that are of concern because of their environmental toxicity. Adsorption is a promising process for the removal of Nap and Phe from water and soil. The riparian zone between a river and a riparian aquifer, which is rich in adsorption medium, may be important for PAH remediation. Nap and Phe may be removed from the surface water through adsorption by the media in the riparian zone. However, there is still a lack of the removal patterns and mechanisms of media in the riparian zone to remediate water contaminated by Nap and Phe simultaneously. In this study, focusing on the typical PAHs (Nap and Phe) as target pollutants, batch static adsorption and desorption experiments of Nap and Phe were carried out to explore the competitive adsorption mechanisms of Nap and Phe in the binary system. Batch dynamic adsorption experiments were conducted to ascertain the adsorption regulation of Nap and Phe in sediments during the recharge of groundwater by river water in a riparian zone. The static adsorption experiment results showed that competitive adsorption of Nap and Phe occurred, and a mutual inhibitory effect of Nap and Phe adsorption was observed in the binary system. Phe had a stronger inhibitory effect on Nap, Phe was preferentially adsorbed on the medium in binary adsorption. The results of batch dynamic experiments showed that, in terms of adsorption, the riparian zone in the study area showed stronger performance for removal of Phe than Nap. The results of this paper could be useful for alleviating Nap and Phe pollution of groundwater and developing treatment protocols for groundwater exposed to Nap and Phe.

Considerations for evaluating innovative stormwater treatment media for removal of dissolved contaminants of concern with focus on biochar

Stormwater from complex land uses is an important contributor of contaminants of concern (COCs) such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), Copper, and Zinc to receiving water bodies. A large portion of these COCs bind to particulate matter in stormwater, which can be removed through filtration by traditional media. However, the remaining dissolved COCs can be significant and require special attention such as engineered treatment measures and media. Biochar is a porous sorbent produced from a variety of organic materials. In the last decade biochar has been gaining attention as a stormwater treatment medium due to low cost compared to activated carbon. However, biochar is not a uniform product and selection of an appropriate biochar for the removal of specific contaminants can be a complex process. Biochars are synthesized from various feedstocks and using different manufacturing approaches, including pyrolysis temperature, impact the biochar properties thus affecting ability to remove stormwater contaminants. The local availability of specific biochar products is another important consideration. An evaluation of proposed stormwater control measure (SCM) media needs to consider the dynamic conditions associated with stormwater and its management, but the passive requirements of the SCM. The media should be able to mitigate flood risks, remove targeted COCs under high flow SCM conditions, and address practical considerations like cost, sourcing, and construction and maintenance. This paper outlines a process for selecting promising candidates for SCM media and evaluating their performance through laboratory tests and field deployment with special attention to unique stormwater considerations.

Assessment of the toxicity of weathered petroleum hydrocarbon impacted soils to native plants from a site in the Canadian Subarctic

Remedial guidelines for petroleum hydrocarbons (PHCs) in soil aid in the mitigation of risks to human health and the environmental. However, some remediation guidelines may overestimate the potential for adverse effects to native plant species, contributing to unnecessary remedial efforts in attempts to meet the guidelines. At sites where PHC-contaminated soils undergo weathering, some PHCs may persist but with decreased bioavailability to organisms. In this study, the toxicity of both coarse and fine-grained subarctic soils, contaminated with weathered PHCs were assessed using five native plant species (Picea mariana, Achillea millefolium, Alnus viridis, Elymus trachycaulus and Salix bebbiana). Soil toxicity tests were conducted in a growth chamber with parameters set to simulate the site's subarctic climate conditions. Reference toxicant tests using boric acid were conducted to provide confidence in the interpretation of the results for the PHC-contaminated soils, and also provide new information on the sensitivities of the four boreal species to boric acid. All plants exhibited reduced growth and germination rates as boric acid concentrations increased. Despite exceeding the Canada-wide standard guidelines for Fraction 3 PHCs, field-collected contaminated soils had no significant negative impacts on the growth (i.e., length, dry weight and emergence) of any of the plant species tested.

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.

In-situ biochar amendment mitigates dietary risks of heavy metals and PAHs in aquaculture products

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are two common contaminant groups of concern in aquaculture products. While biochar amendment can be one of the solutions to immobilize these contaminant in pond sediment, its in situ effectiveness in mitigating the bioavailability, tissue residue, and dietary risk of these contaminants is yet to be tested. In this study, we added wheat straw biochar in sediments of three aquaculture ponds with polyculture of fish and shrimps and employed passive sampling techniques (i.e., diffusive gradient in thin film for HMs and polydimethylsiloxane for PAHs) to assess the diffusion flux and bioavailability throughout the culturing cycle. Reduction in HM concentrations in organisms by biochar after 28 weeks ranged from 17% to 65% for benthic organisms and from 6.0% to 47% for fish. ΣTHQs values of HMs dropped from 2.5 to 2.1 and 1.2 to 0.91 for the two organisms with the initial ΣTHQs value above 1.0. The decrease rates of both the concentrations and ΣTHQs values followed the order of Cu > Cr > Pb > Cd, which was closely correlated with the speciation of HMs in the sediments. ΣPAHs values dropped significantly at the growth stage (20^th week) and the mature stage (28^th week), and, on average, by 34% across all the organisms. Carcinogenic PAHs in aquaculture products decreased dramatically at the seedling stage (12^th week), while there was no significant change observed for the Incremental Lifetime Cancer Risk values. By comparing the freely-dissolved concentrations in pore water of sediments and the overlying water, consistently enhanced diffusion fluxes of HMs and PAHs from water to sediment over the whole culturing cycle were obtained. Our results demonstrated the in situ applicability of biochar amendment to remediating chemical pollution in aquaculture environment and safeguarding quality of aquatic products.

Immobilization of microbes on biochar for water and soil remediation: A review

Biochar has caught great attention over the last decade with the loose and porous structure, and carbon stability provides suitable living conditions for the growth and activity of microorganisms. This review provided a comprehensive summary of biochar immobilization microbe (BIM) in water and soil decontamination. Firstly, the bacterial immobilization techniques including adsorption, entrapping, and covalence methods were exhibited. Secondly, the applications of BIM in water and soil environmental remediation were introduced, mainly including the treatment of organic pollutants, heavy metals, and N/P, among which the most frequently immobilized microorganism was Bacillus. Then, the mechanisms of adsorption, redox, and degradation were analyzed. Finally, pertinent questions for future research of BIM technology were proposed. The purpose of this paper is to provide useful background information for the selection of better biochar fixation microorganisms for water and soil remediation.

Use of activated carbon obtained from sugarcane straw for PAH adsorption - a comparative study with commercial materials

This work evaluates the performance of activated carbon obtained from sugarcane straw (SCAC) as an adsorbent for polyaromatic hydrocarbons (PAHs) present in model wastewater. Two commercial samples of activated carbons with different textural properties were also studied for comparison. The activated carbon prepared from sugarcane straw presents a well-developed porosity with a high surface area, which was comparable to that of one of the commercial samples studied. For all the studied carbons, adsorption followed pseudo-second-order kinetics, and the higher rate constants were found for the SCAC sample for the four PAHs. Sips and Hill isotherms best fitted the adsorption equilibrium data of the PAHs on all activated carbons investigated. The activated carbon obtained from sugarcane straw (SCAC) presented a higher adsorption capacity (2.08 mmol g^-1 for naphthalene, 1.26 mmol g^-1 for fluorene, 1.14 mmol g^-1 for phenanthrene, and 0.98 mmol g^-1 for fluoranthene) when compared to the commercial carbon samples studied in this work as well as for those related in the literature. It confirms that its use of SCAC as an adsorbent for PAHs is a promising application for the valorization of this biomass waste.

A Comprehensive Insight on Adsorption of Polyaromatic Hydrocarbons, Chemical Oxygen Demand, Pharmaceuticals, and Chemical Dyes in Wastewaters Using Biowaste Carbonaceous Adsorbents

Recent trends in adsorption of hazardous organic pollutants including Polyaromatic Hydrocarbons (PAHs), Chemical Oxygen Demand (COD), Pharmaceuticals, and Chemical Dyes in wastewater using carbonaceous materials such as activated carbon (AC) and biochar (BC) have been discussed in this paper. Utilization of biomass waste in the preparation of AC and BC has gained a lot of attention recently. This review outlines the techniques used for preparation, modification, characterization, and application of the above-mentioned materials in batch studies. The approaches towards understanding the adsorption mechanisms have also been discussed. It is observed that in the majority of the studies, high removal efficiencies were reported using biowaste adsorbents. Regarding the full potential of adsorption, varying values were obtained that are strongly influenced by the adsorbent preparation technique and adsorption method. In addition, most of the studies were concentrated on the kinetic, isotherm equilibrium, and thermodynamic aspects of adsorption, suggesting the dominant isotherm and kinetic models as Langmuir or Freundlich and pseudo-second-order models. Due to development in biosorbents, adsorption has been found to be increasingly economical. However, application of these adsorbents at commercial scale has not been adequately investigated and needs to be studied. Most of the studies have been conducted on synthetic solutions that do not completely represent the discharged effluents. This also needs attention in future studies.

Sorption of benzo[a]pyrene by Chernozem and carbonaceous sorbents: comparison of kinetics and interaction mechanisms

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon, highly persistent and toxic and a widespread environmental pollutant. Although various technologies have been developed to remove BaP from the environment, its sorption through solid matrixes has received increasing attention due to cost-effectiveness. The present research compares the adsorption capacity of Haplic Chernozem, granular activated carbon and biochar in relation to BaP from water solution. Laboratory experiments with different initial BaP concentrations in the liquid phase and different ratios of the solid and liquid phases show that Freundlich model describes well the adsorption isotherms of BaP by the soil and both sorbents. Moreover, the BaP isotherm sorption by the Haplic Chernozem is better illustrated by the Freundlich model than the Langmuir equation. The results reveal that the sorption capacity of the carbonaceous adsorbents at a ratio 1:20 (solid to liquid phases) is orders of magnitude higher (13 368 ng mL^-1 of activated carbon and 3 578 ng mL^-1 of biochar) compared to the soil (57.8 ng mL^-1). At the ratio of 0.5:20, the adsorption capacity of the carbonaceous sorbents was 17-45 times higher than that of the soil. This is due to the higher pore volume and specific surface area of the carbonaceous sorbents than soil particles, assessed through scanning electron microscopy. The sorption kinetic of BaP by Chernozem was compared with the adsorption kinetics by the carbonaceous sorbents. Results indicate that the adsorption dynamic involves two steps. The first one is associated with a fast BaP adsorption on the large available surface and inside macro- and meso-pores of the sorbent particles of the granular activated carbon and biochar. Then, the adsorption is followed by a slower process of BaP penetration into the microporous space and/or redistribution into a hydrophobic fraction. The effectiveness of the sorption process depends on both the sorbent properties and the solvent competition. Overall, the granular activated carbon and biochar are highly effective adsorbents for BaP, whereas the Haplic Chernozem has a rather limited capacity to remove BaP from contaminated solutions.

Mitigation of petroleum-hydrocarbon-contaminated hazardous soils using organic amendments: A review

The term "Total petroleum hydrocarbons" (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research.

Utilization of activated carbon derived from waste plastic for decontamination of polycyclic aromatic hydrocarbons laden wastewater

Serious environmental deterioration caused by synthetic waste plastics, and the pollution of freshwater resources are the most alarming and marked challenges of the 21st century. Therefore, immense scientific efforts are being made towards the management of waste plastics and treatment of polluted water. The current study reports on the utilization of waste polyethylene terephthalate (wPET) and waste polystyrene (wPS) for fabrication of activated carbon (AC) and its application for the removal of hazardous polycyclic aromatic hydrocarbons (PAHs) pollutants from water. AC was prepared from wPET and wPS by carbonization under a N₂ atmosphere followed by chemical activation with 1 M KOH and 1 M HCl. The AC was characterized by scanning electron microscopy, surface area analysis, and Fourier transform infrared spectroscopy. Adsorption of PAHs from aqueous solutions through AC was examined by batch adsorption tests. The optimum parameters for maximum adsorption of PAHs were found to be: initial PAHs concentration 40 ppm, 2 h contact time, pH 3, 5, and 7, 50 °C temperature and adsorbent dose of 0.8 g. Kinetic and isotherm models were applied to evaluate the adsorbent capacity for PAHs adsorption. The kinetic study shows that the adsorption of these PAHs onto AC follows pseudo-second-order kinetics. The experimental results demonstrated that the Langmuir isotherm model best fitted the data. The thermodynamic factors calculated such as entropy change (ΔS°), enthalpy change (ΔS°) and free energy change (ΔG°) show that the adsorption process is non-spontaneous and endothermic in nature. Results were also compared with the efficiencies of some commercial adsorbents used in practice. This examination revealed that the novel plastic-derived AC possesses a great potential for elimination and recovery of PAH elimination from industrial wastewater.

Chemical analysis of materials used in pig housing with respect to the safety of products of animal origin

Bedding, environmental enrichment materials and disinfectant powders in pig farming are meant to ensure a hygienic bedding environment or allow pigs to perform explorative behaviour. To our knowledge, no legal regulation exists, that established maximum contents for undesirable substances, such as toxic metals, dioxins or trace elements in these materials, although oral ingestion could be expected. In the present study, a total of 74 materials (disinfectant powders [n = 51], earth/peat [n = 12], biochar [n = 8], recycled manure solids [n = 3]) were analysed for their content of various toxic metals, trace elements, dioxins and polychlorinated biphenyls. The data suggest that, in some samples, trace elements like iron, copper and zinc might have been added intentionally in order to induce physiological effects (iron supply to piglets, copper and zinc as growth promoter in pigs). Moreover, some materials contained high levels of lead, cadmium or arsenic. Consequently, if farm animals repeatedly consume environmental enrichment and bedding materials or disinfectant powders in considerable amounts and these quantities are added to the daily ration, the amount of ingested undesirable substances and trace elements might exceed the maximum levels set for complete feedstuffs, and an elevated transfer into food of animal origin might occur. Future studies are required to address the possible quantitative contribution in the light of feed and food safety. Finally, the excretion of undesirable substances with manure needs to be considered due to their possible accumulation in soils.

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.

Energy recovery from sewage sludge: Product characteristics, heating value prediction and reaction kinetics

Energy recovery from sewage sludge was carried out by using microwave and conventional torrefaction. The microwave torrefaction was carried out by using a laboratory-scale microwave oven that provides single-mode microwave irradiation at 2.45 GHz, and the amount of sewage sludge for each experiment was approximately 20 g. The efficiency of microwave heating can be substantially promoted at higher power level, resulting in higher heating rate and maximum temperature. According to higher energy yield and heating value of torrefied sewage sludge, the optimum power level for bioenergy produced by microwave torrefaction of sewage sludge should be 200 W. Because of lower mass yield and temperature required to obtain the same yield, microwave heating can be more effective than conventional heating for sewage sludge torrefaction. The elemental composition of torrefied sewage sludge at 400 W was similar to that of anthracite, and its low hydrogen and oxygen contents could prevent excessive formation of smoke. Two correlations were obtained to predict the HHV of SS based on proximate and elemental compositions. With the recovery of liquid and gas products as bioenergy, the energy return on investment for microwave torrefaction of sewage sludge can be up to 16.4, much higher than the minimum value required for a sustainable society. Because of lower activation energy but higher pre-exponential factor, microwave heating can be approximately five times faster than conventional heating.

Nitrogen Losses and Potential Mitigation Strategies for a Sustainable Agroecosystem

Nitrogen (N) in the agricultural production system influences many aspects of agroecosystems and several critical ecosystem services widely depend on the N availability in the soil. Cumulative changes in regional ecosystem services may lead to global environmental changes. Thus, the soil N status in agriculture is of critical importance to strategize its most efficient use. Nitrogen is also one of the most susceptible macronutrients to environmental loss, such as ammonia volatilization (NH3), nitrous oxide (N2O) emissions, nitrate leaching (NO3), etc. Any form of N losses from agricultural systems can be major limitations for crop production, soil sustainability, and environmental safeguard. There is a need to focus on mitigation strategies to minimize global N pollution and implement agricultural management practices that encourage regenerative and sustainable agriculture. In this review, we identified the avenues of N loss into the environment caused by current agronomic practices and discussed the potential practices that can be adapted to prevent this N loss in production agriculture. This review also explored the N status in agriculture during the COVID-19 pandemic and the existing knowledge gaps and questions that need to be addressed.

Novel magnetic loofah sponge biochar enhancing microbial responses for the remediation of polycyclic aromatic hydrocarbons-contaminated sediment

Magnetic activated carbon and magnetic biochar have been widely used for contaminants removal due to the advantages of sequestration and recovery. However, the remediation function and microbial response of conductive magnetic carbonaceous materials for treating organic contaminated sediment are poorly understood. In this study we applied novel three-dimensional mesh magnetic loofah sponge biochar (MagLsBC), made from natural agricultural product, to remediate polycyclic aromatic hydrocarbons (PAHs)-contaminated sediment. Compared to other carbon-based materials, MagLsBC achieved the high reduction of PAHs content and bioavailability in sediment by respectively 31.9 % and 38.1 % after 350 days. Microbial analysis showed that MagLsBC amended sediment had different community diversity, structure and enriched dominant species associated with the aromatic hydrocarbon metabolism. And MagLsBC amendment significantly increased the aromatic compounds degradation function, which was not observed in other treatments, and methanogenesis function. Further analysis revealed that the enhanced microbial responses in MagLsBC amended sediment were related with the high conductivity of MagLsBC. These results give the new insights into the effect of magnetic carbon materials on microbial community and organic pollutants degradation function during the long period amendment, demonstrating MagLsBC as an effective material with the biostimulation potential for the risk control of PAHs contamination.

Review on polycyclic aromatic hydrocarbons (PAHs) migration from wastewater

Rapidly increasing global population and increased civilization has increased burden on potable water resources and results in larger volumes of wastewater. Physical wastewater management techniques has advanced for domestic usage and commercial effluent new conceptions about imminent wastewater treatment have been acclaimed for highly carcinogenic polycyclic aromatic hydrocarbon (PAH) compounds. The present review study emphasis on the assessment of several accessible PAHs treatment methods used in wastewater management. The elementary principles, contextual remediation mechanisms and recent development in PAHs removal practices have also been precisely explained. The comprehensive information regarding sources, dispersal, classification, physicochemical properties, PAHs toxicity for humans and aquatics life, conventional treatment procedures, and advanced oxidation processes specified can assist us to identify the PAHs problem and their intensity. The performance evaluation of different removal techniques are discussed in details and found that highest PAHs' reduction for 5-or 6-ring (99%,) while 3-ring (79% reduction) with oxidant dose of 1.64 mL/L using titanium catalyst. In case of MWTPs, with secondary techniques, the average removal efficiency found in the range of 81.1-92.9% while for AOPs are 32-99.3%. Here, overall yield through AOPs most suitable if process used with some catalyst enhanced the yield as well and suitable for high ring as well as low ring PAHs. Among various processes, advanced oxidation and catalytic oxidation processes are the most valuable and promising techniques for PAHs removal. Based on the given evidences, the AOPs coupled with catalysts have been decided as the most competent design for wastewater PAHs treatment.

A critical review on the biochar production techniques, characterization, stability and applications for circular bioeconomy

•

Recent research on remediation of toxic pollutants by biochar has been summarized.

•

The production techniques of the biochar have been narrated.

•

Biochar properties, stability and its environmental issues have been analysed.

•

Applications of biochar in soil fertility and removing pollutants have been reported.

•

The major stumbling block in biochar production is cost of production.

There is an upsurge enthusiasm for utilizing biochar produced from waste-biomass in different fields, to address the most important ecological issues. This review is focused on an overview of remediating harmful contaminants utilizing biochar. Production of biochar utilizing various systems has been discussed. Biochar has received the consideration of numerous analysts in building up their proficiency to remediate contaminants. Process parameters are fundamentally answerable for deciding the yield of biomass. Biochar derived from biomass is an exceptionally rich wellspring of carbon produced from biomass utilizing thermal combustion. Activating biochar is another particular region for the growing utilization of biochar for expelling specific contaminations. Closed-loop systems to produce biochar creates more opportunities. Decentralized biochar production techniques serve as an effective way of providing employment opportunities, managing wastes, increasing resource proficiency in circular bioeconomy. This paper also covers knowledge gaps and perspectives in the field of remediation of toxic pollutants using biochar.

Design and Validation of Passive Environmental DNA Samplers Using Granular Activated Carbon and Montmorillonite Clay

Environmental DNA (eDNA) analysis is gaining prominence as a tool for species and biodiversity monitoring in aquatic environments. eDNA shed by organisms is captured in grab samples, concentrated by filtration, extracted, and analyzed using molecular methods. Conventional capture and filtration methods are limited because (1) filtration does not capture all extracellular DNA, (2) eDNA can degrade during sample transport and storage, (3) filters often clog in turbid waters, reducing the eDNA captured, and (4) grab samples are time sensitive due to pulse eDNA inputs. To address these limitations, this work designs and validates Passive Environmental DNA Samplers (PEDS). PEDS consist of an adsorbent-filled sachet that is suspended in water to collect eDNA over time. Both extracellular and cellular DNA are captured, and the extracellular DNA is protected from degradation. The eDNA captured over time may be more representative than a grab sample. Two adsorbents, Montmorillonite Clay (MC) and Granular Activated Carbon (GAC), are tested. In laboratory experiments, MC-PEDS adsorbed five times more extracellular DNA and desorbed up to four times more than GAC-PEDS (despite high levels of eDNA loss during desorption). In microcosm and field experiments, GAC-PEDS captured over an order of magnitude more eDNA than MC-PEDS. Field results further validated PEDS as an effective eDNA capture method compared to conventional methods.

The Trends in Research on the Effects of Biochar on Soil

The present study used bibliometric methods to analyze the literature regarding the biochar effects on soil that are included in the Web of Science Core Collection database and quantified the annual number of publications in the field and distribution of publications. Using CiteSpace as a visual analytic software for the literature, the distribution of the subject categories, author collaborations, institution collaborations, international (regional) collaborations, and cocitation and keyword clustering were analyzed. The results showed the basic characteristics of the literature related to the effects of biochar on soil. Furthermore, the main research powers in this field were identified. Then, we recognized the main intellectual base in the domain of biochar effects on soil. Meanwhile, this paper revealed the research hotspots and trends of this field. Furthermore, focuses of future research in this field are discussed. The present study quantitatively and objectively describes the research status and trends of biochar effects on soil from the bibliometric perspective to promote in-depth research in this field and provide reference information for scholars in the relevant fields to refine their research directions, address specific scientific issues, and help scholars to seek/establish relevant collaborations in their fields of interests.

Comparative Assessment of Thermo-Syngas Fermentative and Liquefaction Technologies as Waste Plastics Repurposing Strategies

The present study comparatively investigates the potential of waste plastic utilization as a feedstock for the production of liquid fuels to satisfy the rising liquid fuel demands of the transportation industry while simultaneously resolving the global plastic waste pollution challenge. For the first time, therefore, conceptual models simulating the production of transportation fuels of ethanol and gasoline from waste plastics via the technologies of thermo-syngas fermentation and hydrothermal liquefaction were assessed using classic technoeconomic assessment methods. The conceptual models were developed based on existing experimental data as obtained from the literature and simulated using ASPEN Plus as the preferred process simulation tool. This study demonstrated the technical viability of both conversion pathways with the hydrothermal liquefaction (HTL) of waste plastics for gasoline production shown to constitute a more economically preferable pathway. This was because the HTL of waste plastics presented a higher internal rate of return (IRR) value and a lower unit processing cost of 51.3% and USD 0.38 per kg compared to the thermo-syngas fermentation pathway that presented an IRR value and a unit processing cost value of 22.2% and USD 0.42 per kg, respectively. Payback periods of 5 years and 2 years were also determined as vital to recoup initial capital invested in the thermo-syngas fermentation project and the HTL project, respectively. Therefore, this study provides a basis for further work regarding waste plastic management strategies while offering a useful guide for policy makers in determining the most cost-effective way to utilize waste plastic and thus promote favorable environmental outcomes.

Experimental investigations and numerical modelling of in-situ reactive caps for PAH contaminated marine sediments

The present study compared numerical modelling and experimental investigations to evaluate the effectiveness of in-situ reactive capping for marine sediments contaminated by polycyclic aromatic hydrocarbons (PAHs). As a case study, sediment samples from Mar Piccolo (Italy) were analyzed and experiments were undertaken using batch columns. Two types of capping amendments were tested: AquaGate® + 5 % of powdered activated carbon (AG PAC) and Organoclay Reactive Core Mat (OC RCM). The column tests were carried out for 20 days, obtaining a short-term PAH distribution for three cases analysed, which compared the application of the two caps with no intervention. In parallel, in order to evaluate the intervention long term efficacy, an ad-hoc multilayered model predicting PAH concentrations into the sediments and the overlying water column was developed and validated with the experimental results. Both capping systems considerably reduced PAH concentrations in the overlying water, with the highest performance seen in AG PAC for benzo[a]pyrene (99 %) and anthracene (72 %); results also confirmed in the model predictions. In addition, the numerical simulations indicated a good efficiency of both caps over time, obtaining PAH values below the threshold limit in the long term. Although further experiments need to be developed accounting for multiple contamination competitiveness.

Effect of biochar amendment on sorption-desorption and dissipation of 17α‑ethinylestradiol in sandy loam and clay soils

Animal manure application in agricultural land has caused the release of steroid estrogens in the soil environment and further movement to aquatic systems. The objective of this study was to investigate the effects of biochar addition on sorption-desorption and dissipation behaviors of 17α‑ethinylestradiol (EE2) in two different textured soils. A Commerce sandy loam and a Shakey clay were selected and subjected to sterilization. Soil samples with and without sterilization were reacted with a series of EE2 solutions of different concentrations for sorption followed by desorption and quantification using HPLC-MS/MS. Long-term dissipation of EE2 in the same soils was also evaluated over a 30-d incubation. Biochar amendment increased the maximum EE2 sorption capacity but decreased its water desorption in both sandy loam and clay soils. On other hand, biochar addition increased the K_oc in the clay soil which had low EE2 sorption efficiency but decreased K_oc in the sandy loam which had high EE2 sorption efficiency. Biochar did significantly increase both desorbable and non-extractable fractions of EE2, while it reduced the bioavailability of EE2 to microbial degradation. The dissipation of EE2 in non-sterilized soils fit to the first-order kinetic model, whereas it was better described by zero-order kinetic for sterilized soil. Biochar increased the half-life of EE2 dissipation in non-sterilized Commerce sandy loam soil by 48% (from 3.63 to 5.37 d) and in non-sterilized Sharkey clay soil by 67% (from 2.28 to 3.81 d). Overall, this study demonstrated positive impacts of biochar on the retention of estrogen hormones in soils.

Effects of the pyrolysis temperature on the biotoxicity of Phyllostachys pubescens biochar in the aquatic environment

The use of biochar as an adsorbent for environmental remediation has been attracting increasing interest. However, biochar can contain contaminants such as polycyclic aromatic hydrocarbons (PAHs) and metals (e.g., Cu, Pb, and Zn). We prepared Phyllostachys pubescens biochars at temperatures between 400 and 700 °C. The biochars were used in bioassays using Vibrio qinghaiensis Q67, Daphnia magna, Pseudokirchneriella subcapitata, and Limnodrilus hoffmeisteri to characterize the toxicities and effects of the biochars. The PAH, Cu, Pb, and Zn contents of the biochars were 8.59-14.67, 1.82-3.26, 1.17-3.53, and 8.76-16.47 mg/kg, respectively. The biochars gave maximum P. subcapitata, D. magna, and V. qinghaiensis Q67 inhibition rates of 6.47%, 6.70%, and 29.87%, respectively. The biochars produced at high pyrolysis temperatures (≥600 °C) had low acute biotoxicities to L. hoffmeisteri and barely affected L. hoffmeisteri biomass, reproduction, and lipid content. The biochars may therefore be suitable for sediment remediation.

Adsorption and desorption of heavy metals by the sewage sludge and biochar-amended soil

The goal of the study was to evaluate the application of biochar (BC) to the sewage sludge (SL) on the adsorption and desorption capacity of Cd(II), Cu(II), Ni(II) and Zn(II). The effect of biochar contribution in the sewage sludge (2.5, 5 and 10%) was investigated. The isotherms data were fitted to the Langmiur (LM), Freundlich (FM) and Temkin (TM) models. The best fitting for kinetic study was obtained for the pseudo-second-order equation. The best fitting of the experimental data was observed for the LM in the case of SL and BC, and for the FM in the case of SL- and SL/BC-amended soil. SL was characterized by even four-order higher sorption capacity than BC. The addition of the BC to the SL and next to the soil increased the adsorption capacity of the soil and the SL-amended soil. In the case of all investigated potentially toxic elements (PTEs), the highest adsorption capacity was achieved for SL-amended soil in comparison with the control soil. In the case of other experimental variants, the adsorption capacity of metal ions was as follows: 2.5% BC > 5.0% BC > 10% BC. The negative correlation between hydrated radius of metal ions and the kinetics of sorption was observed. However, the desorption of PTEs from BC/SL-amended soil was significantly lower than for SL-amended soil (except of Cd) and non-amended soil. It can be concluded that the addition of the biochar enhanced the immobilization of PTEs and reduced their bioavailability and mobility in the soil amended by the sewage sludge.

Lindane and hexachlorobenzene sequestration and detoxification in contaminated sediment amended with carbon-rich sorbents

Sediment represents a sink for toxic and persistent chemicals such as hexachlorobenzene (HCB) and lindane (γ-HCH). This paper investigates the possibility of reducing the risks associated with the presence of these pollutants in sediments by amending the sediment with carbon-rich materials (activated carbon (AC) and humus (HC)) to sequester the contaminants and render them biologically unavailable. The effects of the dose and contact time between the sediment and the carbon-rich amendments on the effectiveness of the detoxification are estimated. Four doses of carbon-rich amendments (0.5-10%) and four equilibration contact times (14-180 days) were investigated. Results have shown that the bioavailable fraction of γ-HCH and HCB decreased significantly in comparison to the unamended sediment. Regarding the AC amendments, almost 100% for both compounds; and for HC amendments around 95% for γ-HCH, and 75% for HCB. Aging caused further reductions in the bioavailable fraction, compared to the untreated sediment. Phytotoxicity tests showed that Zea mays accumulated significantly higher amount of γ-HCH and HCB from unamended sediment, comparing to Cucurbita pepo and Lactuca sativa. Toxicity of HC and AC amended sediment assessed by Vibrio fischeri luminescence inhibition test and by measuring Zea mays germination and biomass yield was significantly reduced in the amended sediment samples. γ-HCH and HCB accumulation in the Zea mays biomass in the unamended sediment were a significantly higher than in the all HC and AC amended sediment. Both sorbents show potential to be used as remediation agents for organically contaminated sediment, but AC exhibited the better performance.

Four decades since the ban, old urban wastewater treatment plant remains a dominant source of PCBs to the environment

Despite the ban on new manufacture and commercial use of PCBs, municipal sewer systems continue to serve as ongoing secondary sources for contamination in receiving water bodies. Ongoing PCB sources have made it difficult to achieve desired recovery after implementation of sediment cleanup efforts. We report on a 16-month surveillance to determine the inputs, fate, and export of PCBs within a municipal waste collection/treatment system by strategic sampling of the freely-dissolved and biosolids-associated PCBs. The total PCBs entering the treatment plant was found to be 170 g/day of which 100 g/day exited the plant associated with the biosolids and 5.2 g/day was discharged in the form of freely-dissolved PCBs in the effluent. A net loss of 68 g/day was calculated for the plant, attributable to volatilization and biodegradation. Freely dissolved PCBs in the treated effluent was an order of magnitude higher than the water quality criteria for the protection of human health through fish consumption and found to be a major contributor to the dissolved concentration in the receiving river. Predicted bioaccumulation in fish from dissolved PCBs in the effluent exceeded the threshold for human consumption. The biosolids, currently land-applied as fertilizer, contained an average PCB concentration of 760 μg/kg. The sludge produced in this treatment plant is processed in large anaerobic digesters and changes to the homolog distribution point to some microbial dechlorination. Application of biosolids to clean agricultural soil resulted in a 6-fold increase in PCB levels in the earthworm E. fetida which could be eliminated by the amendment of 1% by weight of activated carbon.

Linking bioavailability and toxicity changes of complex chemicals mixture to support decision making for remediation endpoint of contaminated soils

A six-month laboratory scale study was carried out to investigate the effect of biochar and compost amendments on complex chemical mixtures of tar, heavy metals and metalloids in two genuine contaminated soils. An integrated approach, where organic and inorganic contaminants bioavailability and distribution changes, along with a range of microbiological indicators and ecotoxicological bioassays, was used to provide multiple lines of evidence to support the risk characterisation and assess the remediation end-point. Both compost and biochar amendment (p = 0.005) as well as incubation time (p = 0.001) significantly affected the total and bioavailable concentrations of the total petroleum hydrocarbons (TPH) in the two soils. Specifically, TPH concentration decreased by 46% and 30% in Soil 1 and Soil 2 amended with compost. These decreases were accompanied by a reduction of 78% (Soil 1) and 6% (Soil 2) of the bioavailable hydrocarbons and the most significant decrease was observed for the medium to long chain aliphatic compounds (EC_16-35) and medium molecular weight aromatic compounds (EC_16-21). Compost amendment enhanced the degradation of both the aliphatic and aromatic fractions in the two soils, while biochar contributed to lock the hydrocarbons in the contaminated soils. Neither compost nor biochar affected the distribution and behaviour of the heavy metals (HM) and metalloids in the different soil phases, suggesting that the co-presence of heavy metals and metalloids posed a low risk. Strong negative correlations were observed between the bioavailable hydrocarbon fractions and the ecotoxicological assays suggesting that when bioavailable concentrations decreased, the toxicity also decreased. This study showed that adopting a combined diagnostic approach can significantly help to identify optimal remediation strategies and contribute to change the over-conservative nature of the current risk assessments thus reducing the costs associated with remediation endpoint.

Thermodynamic assessment of (semi-)volatile hydrophobic organic chemicals in WWTP sludge - combining solid phase microextraction with non-target GC/MS

Applying WWTP sludge on arable soil has clear benefits from a resource recycling point of view but can potentially also lead to contamination of soil, agricultural products and the environment. The sludge contains a complex mixture of particularly hydrophobic organic chemicals (HOCs) that sorb to the organic matter. Equilibrium sampling was recently applied to the measurement of chemical activities of polycyclic aromatic hydrocarbons (PAHs) in secondary and digested sludge, and clear activity increases due to the anaerobic digestion treatment were observed. In the present study we extend this work to a large number of (semi-)volatile HOCs by combining automated headspace solid phase microextraction with non-targeted gas chromatography mass spectrometry. Chemical activity ratios were determined between sludge from the different stages of a WWTP and after co-composting with garden waste and sorbent amendment with activated carbon (AC) and biochar (BC). Generally, chemical activities increased from primary, to secondary, to digested sludge and the level in the dewatered sludge was not significantly different from the level in the digested sludge. Decamethylcyclopentasiloxane (D5) behaved differently as the level was similar until the dewatering step, where it increased 4-fold. The results confirmed the earlier observation that anaerobic digestion increased chemical activity, now for a broader range of chemicals, and showed that co-composting was effective in reducing chemical activities of most of the tested (semi-)volatile organic chemicals. Of the studied compounds, activities of D5 and a musk fragrance were reduced the least by co-composting.

Remediation effectiveness of Phyllostachys pubescens biochar in reducing the bioavailability and bioaccumulation of metals in sediments

Biochar has potential for application for in situ metal-contaminated sediment remediation, mainly because of its cost-effectiveness. In this study, the effectiveness of Phyllostachys pubescens (PP) biochar for immobilization of cadmium (Cd) chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) by decreasing the bioavailable fraction was investigated using a series of laboratory sediment remediation microcosms. The results demonstrated that biochar could significantly reduce the bioavailable fraction of metals (except for Cr) by diffusive gradients in thin film (DGT) measurement in porewater. Additionally, amended sediment treated with 15% w/w biochar resulted in 79.71%, 73.20%, 54.86%, 49.75%, 31.16% and 0.99% reductions in the acid-soluble fraction for Cu, Pb, Ni, Zn, Cd, and Cr, respectively. Similarly, bioaccumulation of metals (except for Cr) by Limnodrilus hoffmeisteri was reduced by 18.45%-59.15% in biochar amended sediment. PP biochar at 15% could also reduce the inhibition or lethality rate by 37.5%, 18.1% and 36.3% for Chlorella vulgaris, Daphnia magna and luminescent bacteria Vibrio qinghaiensis, respectively. Overall, these results demonstrate the potential for biochar application for in situ sediment remediation.

Adsorption of Cadmium on Degraded Soils Amended with Maize-Stalk-Derived Biochar

Biochar has been extensively proven to distinctively enhance the sorption capacity of both heavy metal and organic pollutants and reduce the related environmental risks. Soil pollution and degradation widely coexist, and the effect of biochar addition on adsorption behavior by degraded soils is not well understood. Four degraded soils with different degrees of degradation were amended with maize-stalk-derived biochar to investigate the adsorption of cadmium using batch methods. The maximum adsorption capacity (Q_m) of degraded soil remarkably decreased in comparison with undegraded soil (5361 mg·kg⁻¹→170 mg·kg⁻¹), and the Q_m of biochar increased with increasing pyrolysis temperature (22987 mg·kg⁻¹→49016 mg·kg⁻¹) which was much higher than that of soil. The addition of biochar can effectively improve the cadmium adsorption capacity of degraded soil (36–328%). The improving effect is stronger when increasing either the degradation level or the amount of added biochar, or the pyrolysis temperature of biochar. Contrary to the general soil–biochar system, adsorption of Cd was not enhanced but slightly suppressed (7.1–36.6%) when biochar was incorporated with degraded soils, and the adsorptivity attenuation degree was found to be negatively linear with SOM content in the degraded soil–biochar system. The results of the present study suggest that more attention on the adsorption inhibition and acceleration effect difference between the soil–biochar system and the degraded soil–biochar system is needed.

Effects of biochars on the fate of acetochlor in soil and on its uptake in maize seedling

Biochar (BC) can alter the fate and bioavailability of pesticides in soil. In this study, the effects of three types of BCs (made of crofton weed, wood chips and rice hull) on the sorption of acetochlor, a common herbicide, were investigated. The acetochlor sorption constants (K_f value) were 309.96 μg^1-nL^n/kg (biochars made of ricehull, BCR), 3.54 μg^1-nL^n/kg (biochars made of crofton weed, BCH) and 2.27 μg^1-nL^n/kg (biochars made of wood chips, BCW). The persistence of acetochlor was 8 times greater when 1% BCR was added to the soil. Moreover, the half-life of acetochlor increased with increasing amounts of BC in the soil. The soil was amended with BCH (made of crofton weed) for two different aging period (10 d and 20 d) to evaluate the effects of aged BC on acetochlor accumulation in maize seedlings (Zea mays L). Amendment with 10 d-aged BCH in soil decreased the bioaccumulation of acetochlor. However, the concentrations and bioconcentration factors in maize cultivated in 20 d-aged BCH-amended soils were significantly higher than those in soil with no BCH amendments and with 10 d-aged BCH amendments. These results imply that BC aged in soil for a long period can increase the bioaccumulation of acetochlor in plants and the influences of BC on environmental risks of pesticides must be further clarified.