Roles of pyrolysis on availability, species and distribution of Cu and Zn in the swine manure: chemical extractions and high-energy synchrotron analyses

The influence of biomass type on hydrothermal carbonization: Role of calcium oxalate in enhancing carbon sequestration of hydrochar

Addressing climate change through effective carbon sequestration strategies is critical. This study presents an investigation into the hydrothermal carbonization (HTC) and co-hydrothermal carbonization (Co-HTC) of invasive plants (IPs) to produce hydrochars to unveil the significant impact of biomass type and unique mineral on the stability of hydrochars. Nine hydrochars were produced from six IPs, utilizing both single and mixed biomass. A key finding is the observable that calcium oxalate forms as a surface mineral during HTC through different characterization techniques, the presence of which notably influenced the stability of hydrochars, resulting in enhanced thermal (highest R50 = 0.81) and chemical (lowest carbon loss rate = 4.02%) stability of hydrochars, possibly acting as a protective layer. Besides, a positive correlation was established between the yield of hydrochars and the lignin content of the original biomass. It is also observed that Co-HTC of plant materials rich in Ca2+ can enhance the formation of calcium oxalate minerals. This is likely due to their synergistic role in the HTC process, promoting the release of more C2O42- and Ca2+. Our results signify the crucial role of biomass composition in the HTC process and spotlight the potential of calcium oxalate in augmenting hydrochar stability. This study offers valuable insights that bolster the theoretical framework for employing hydrochar derived from IPs as a potent material for carbon sequestration.

Effects of ferrous sulfate modification on the fate of phosphorous in sewage sludge biochar and its releasing mechanisms in heavy metal contaminated soils

Modifications of sludge biochar with metal-based materials can enhance its fertilizing efficiency and improve safety. To elucidate the effects of ferrous sulfate modification on the fate of phosphorus in sludge biochar and its effect on phosphorus fractionation in soil, we investigated the changes in fractionation and bioavailability of phosphorus in modified sludge biochar and studied the changes in soil characteristics, microbial diversity and response, bioavailability, plant uptake of phosphorus, and heavy metals in contaminated soils after treatment with ferrous sulfate modified sludge biochar. The results demonstrated that ferrous sulfate modifications were conducive to the formation of moderately labile phosphorus in sludge biochar, and the concentrations increased by a factor of 2.7 compared to control. The application of ferrous sulfate-modified sludge biochar to alkaline heavy metal-contaminated soils enhanced the bioavailable, labile, and moderately labile phosphorus contents by a factor of 2.9, 3.0, and 1.6, respectively, whereas it obviously reduced the leachability and bioavailability of heavy metals in soils, exhibited great potentials in the fertilization and remediation of actual heavy metal-contaminated soils in mining areas. The biochar-induced reduction in soil pH, enhancement of organic matter, surface oxygen-containing functional groups, the abundance of Gammaproteobacteria, and its phosphonate degradation activity were primarily responsible for the solubilization of phosphorus from modified biochar in heavy metal-contaminated soils.

Pig manure biochar for contaminated soil management: nutrient release, toxic metal immobilization, and Chinese cabbage cultivation

Pig manure could be an effective fertilizer source for soil, but with high concentrations of xic elements. It has been shown that the pyrolysis method could largely reduce the environmental risk of pig manure. However, the comprehensive analysis of both toxic metals immobilization effect and environmental risk of pig manure biochar applied as a soil amendment is rarely addressed. To address the knowledge gap, this study was carried out with pig manure (PM) and pig manure biochar (PMB). The PM was pyrolyzed at 450 ℃ and 700 ℃, the corresponding biochar was abbreviated as PMB450 and PMB700, respectively. The PM and PMB were applied in a pot experiment growing Chinese cabbage (Brassica rape L. ssp. Pekinensis) with clay-loam paddy soil. The application rates of PM were set at 0.5% (S), 2% (L), 4% (M) and 6% (H). With the equivalent mass principle, PMB450 and PMB700 were applied at 0.23% (S), 0.92% (L), 1.84% (M), 2.76% (H), and 0.192% (S), 0.7% (L), 1.4% (M), 2.1% (H), respectively. Parameters of Chinese cabbage biomass and quality, total and available concentrations of toxic metals in soil, and soil chemical properties were systemically measured. The main results of this study showed that compared with PM, PMB700 was more effective than PMB450, which induced the highest reductions of Cu, Zn, Pb, and Cd contents in cabbage by 62.6%, 73.0%, 43.9%, and 74.3%, respectively. Both PM and PMB increased the total contents of metals (Cu, Zn, Pb, and Cd) in soil, and PMB decreased the mobility of Cu, Zn, Pb, and Cd at high application rates (≥2%). Treatment with H-PMB700 reduced CaCl₂ extractable Cu, Zn, Pb, and Cd by 70.0%, 71.6%, 23.3%, and 15.9%, respectively. For Cu, Zn, Pb, and Cd fractions with BCR extraction, PMB treatments, especially PMB700, were more effective than PM in decreasing the available fractions (F1 +F2 +F3) at high application rates (≥2%). Overall, pyrolysis with high temperature (e.g., 700 ℃) could significantly stabilize the toxic elements in PM and enhance PM's effect on toxic metals immobilization. The marked effects of PMB700 on toxic metal immobilization and cabbage quality improvement might be attributed to high ash contents and liming effect.

Particle size of biochar significantly regulates the chemical speciation, transformation, and ecotoxicity of cadmium in biochar

The pyrolysis of biomass containing excessive heavy metals is likely to produce heavy metal contaminated biochar (BC). Although multiple lines of evidence indicate that higher charring temperature leads to enhanced immobilization of heavy metals in BC, we find that particle size could also play a critical role in the content of heavy metals in BC and BC ecotoxicity. Here, BC derived from cadmium (Cd) enriched rice straw was prepared at different temperatures (300-600 °C) and divided into macro-, colloidal-, and nano-sized fractions, respectively. The content and chemical forms of Cd in BC fractions as well as related algal toxicity were examined. The results show that for the same temperature BC the content of Cd followed an order of colloidal-BC > macro-BC > nano-BC; and the residual fractions of Cd significantly decreased (3.47-16.08%) while that of acid soluble and reducible fractions significantly increased (4.13-16.51% and 0.24-1.71%, respectively) with decreasing particle size of BC. Consistently, colloidal-BC exhibited the highest ecotoxicity for Scenedesmus obliquus. The acid soluble fractions of Cd in macro- and colloidal-BC played a dominating role in their algal toxicity (p < 0.05). However, the ecotoxicity of nano-BC was more dependent on the total content of Cd than specific fractions probably due to the phagocytosis by algal cells. These results indicate that the chemical forms and ecotoxicity of Cd in BC could be remarkably modified by its particle size, which has profound implications for understanding the behavior and potential risk of heavy metal contaminated BC in the environment.

Comparative study on the characteristics and environmental risk of potentially toxic elements in biochar obtained via pyrolysis of swine manure at lab and pilot scales

Pyrolysis is considered as a promising method to immobilize potentially toxic elements (PTEs) in animal manures. However, comparative study on characteristics and environmental risk of PTEs in biochar obtained by pyrolysis of animal manure at different reactors are lacking. In this study, swine manure was pyrolyzed at 300-600 °C in a lab-scale or pilot-scale reactor with the aim to investigate their effects on characteristics and environmental risk of As, Cd, Cu, Ni, Pb, and Zn in swine manure biochar. Results showed that biochars produced from pilot scale had lower pH and carbon (C) content but higher oxygen (O) content than those from lab scale. Biochars from pilot scale had higher total PTEs (except Cd) concentrations and releasable PTEs (except Pb) but lower CaCl₂-extractable PTEs and phytotoxicity germination index (GI) to radish seedings than those from lab scale. Chemical speciation analysis indicated that PTEs in biochar produced from pilot-scale fast pyrolysis at 400 °C had higher percentage of more stable fraction (F5 fraction) and lower potential ecological risk index (RI) than those from lab-scale slow pyrolysis. These findings demonstrated that bioavailability and potential ecological risk of PTE in swine manure biochar were greatly decrease in the pilot-scale pyrolysis reactor and the optimum temperature was 400 °C considering the lowest potential ecological risk index.

Application of co-pyrolysis biochar for the adsorption and immobilization of heavy metals in contaminated environmental substrates

Heavy metal pollution has been considered as a serious threat to the environment and human in the past decades due to its toxic and unbiodegradable properties. Recently, extensive studies have been carried out on the removal of heavy metals, and various adsorption materials have been successfully developed. Among, biochar is a promising option because of its advantages of various biomass sources, abundant microporous channels and surface functional groups, as well as its attractive economic feasibility. However, the application of pristine biochar is limited by its low adsorption capacity and nonregenerative property. Co-pyrolysis biochar, produced from the pyrolysis of biomass with the addition of another biomass or non-biomass precursor, is potential in overcoming the limitation of pristine biochar and achieving superior performance for heavy metal adsorption and immobilization. Therefore, this article summarizes the recent advances in development and applications of co-pyrolysis biochar for adsorption and immobilization of various heavy metals in contaminated environmental substrates. In details, the production, characteristics and advantages of co-pyrolysis biochar are initially presented. Subsequently, the adsorption behaviors and mechanisms of different heavy metals (including Hg, Zn, Pb, Cu, Cd, Cr, As, etc.) in flue gas and wastewater by co-pyrolysis biochar are reviewed, as well as factors influencing their adsorption capacities. Meanwhile, the immobilization of heavy metals in both biochar itself and contaminated soils by co-pyrolysis biochar is discussed. Finally, the limitations of current studies and future prospects are proposed. It aims at providing a guideline for the exploitation and application of cost-effective and environmental-friendly co-pyrolysis biochar in the decontamination of environmental substrates.

Multi-functional biochar preparation and heavy metal immobilization by co-pyrolysis of livestock feces and biomass waste

Biomass waste is a desirable additive in livestock feces biochar preparation due to its easy access, better moisture adjustment, and abundant organic content. In the present study, co-pyrolysis of livestock feces (PM: pig manure, CM: chicken manure) and biomass wastes (WC: wood chips, BS: bamboo sawdust, RH: rice husk, and CH: chaff) with different blending ratios was conducted at 600 °C to investigate the biochar characteristic and Cu/Zn immobilization performances. The results showed that WC and BS have more significant effect on the increase in fixed carbon content and heating value and the decrease in ash content of biochar. The biochar with lower pH and electrical conductivity is obtained from co-pyrolysis of manure with RH and CH. Compared with CM-based biochar, PM-based biochar presented better potential as fuel and soil remediation considering the higher heating value and lower aromatic H/C ratio. Specially, the residual fractions of Cu and Zn in PM biochar increased from 73.09% and 65.54% to 90.68% and 72.31% after 10 wt% BS addition and those in CM biochar increased from 81.07% and 73.57% to 88.87% and 84.11% after 10 wt% WC addition, which induced the lowest environmental risk of biochar. This work provided a strategy and direction for targeted enhancement in biochar characteristics with selective biomass addition during manure pyrolysis, which is beneficial to the local treatment and utilization of farm wastes.

Effects of added calcium-based additives on swine manure derived biochar characteristics and heavy metals immobilization

Although pyrolysis is a promising way for treating animal manure, the application is restricted with some limitations of biochar. To improve the quality of biochar derived from swine manure and enhance the immobilization of heavy metals (Cu and Zn) in it, swine manure was mixed with four types of Ca-based additives (CaO, CaCO₃, Ca(OH)₂, and Ca(H₂PO₄)₂) prior to pyrolysis at 300-700 °C. The thermogravimetric characteristics of swine manure were obviously influenced The addition of CaO, CaCO₃, and Ca(OH)₂ during the whole decomposition process. Furthermore, with the addition of CaO and Ca(OH)₂, the emission of CO₂ and CO was substantially decreased at 200-500 °C, whereas the formation of CO, H₂, CO₂, and CH₄ was drastically increased at 600-800 °C. The biochar produced with CaO addition had the highest pH, surface area and carbon content. Moreover, by addition of Ca-based additives, except for Ca(H₂PO₄)₂, the transformation of labile Cu and Zn to the stable fraction was promoted, and the leachability and environmental risk of them were simultaneously reduced. In contrast, CaO and Ca(OH)₂ were more favorable for the immobilization of Cu and Zn than CaCO₃. Our study indicated that the catalytic pyrolysis using CaO was an effective and valuable method of animal manure treatment.

Influence of pyrolysis temperature on the properties and environmental safety of heavy metals in chicken manure-derived biochars

Animal manures usually contain high contents of heavy metals (HMs) and thus pose a considerable threat to human health and environment when applied to soil. In this study, the effect of pyrolysis temperature (300 °C, 400 °C, 500 °C, 600 °C, and 700 °C) on the properties of biochar produced from chicken manure was studied. In addition, the response of speciation, bioavailability, leachability, and environmental risk of HMs in biochar to different pyrolysis temperature was investigated. The results showed that biochars pyrolyzed at high temperatures generally had high pH, ash content, surface area, and stability. As the pyrolysis temperature increased, the total concentrations of Cu, Zn, Cr, and Ni continually increased, whereas those of Pb and Cd initially increased and then decreased. Moreover, the transformation of the bioavailable fractions of HMs into stable fractions obviously increased with increasing pyrolysis temperature. Thus, pyrolysis at high temperature led to a further decrease in the bioavailability, leachability, and environmental risk of six HMs, as shown by DTPA, TCLP, and the potential ecological risk index. Overall, it is convincing that that 700 °C is the optimal temperature when considering the quality and environmental safety of biochar derived from chicken manure.

Copper Speciation Evolution in Swine Manure Induced by Pyrolysis

Swine manures generally contain high levels of copper (Cu) resulting from its use as a growth promoter in feedstuff. Pyrolysis can further concentrate Cu whereas decrease its available fraction in swine manures. Here we investigated the speciation transformation of Cu and associated elements in swine manures induced by pyrolysis using multiple X-ray absorption spectroscopies. Results showed that over 82% of Cu existed as Cu(I)-S and Cu(I)-thiolate complexes in swine manures, which were transformed into stable Cu(I)₂S during pyrolysis at a low temperature of 300 °C and partially oxidized and desulfurized into Cu(II) compounds at a high temperature of 500 °C. The speciation evolution of Cu in swine manures was consistent with the speciation distribution of sulfur in feedstuff and its following changes in swine manures during pyrolysis. About 58% of phosphorus existed as CaHPO₄ and struvite in swine manures, which were gradually transformed into stable Ca-bound species such as hydroxyapatite during pyrolysis. The formation of stable phosphate, together with concentrated carbonates, significantly decreased the available Cu in pyrolyzed manures. These findings suggested that the high levels of S and P in feedstuff profoundly affected the speciation of Cu in the swine manures and derived biochars. This study has important implications to our understanding of the behaviors of heavy metals in manure-derived biochars once entering soil environments.

Evolution of heavy metals during thermal treatment of manure: A critical review and outlooks

Manure treatment has become a focal issue in relation to current national policies on environmental and renewable energy matters. Heavy metals can be excreted with the animal manure, contributing to pollution of soil and water. Therefore, animal manure needs proper treatment before application to agricultural soils. Here, we review the species transformation of HMs and fate during incineration, pyrolysis, gasification and hydrothermal processing of animal manures. During thermal processes, 75%-90% of thermally stable HMs such as Cr, Ni, and Mn were concentrated in the solid-phase. HMs with less thermal stability such as Cd, As, Hg, and Pb are inclined to concentrate in the aqueous phase and gas phase, accounting for less than 5% of their total concentrations. In general, thermal processes transform HMs in the exchangeable fraction with high biotoxicity to oxidizable fraction or residual fraction with less bioavailability. In addition, the operating conditions and co-processing with other materials may influence the species transformation of HMs. Finally, recommendations for future research on the proper disposal and utilization of animal manure are proposed. More large-scale experiments are required to elucidate the precise mechanism behind the immobilization of HMs. The influence of additives (catalysts and HM stabilizers) and the influence of the type of solvent on HM transformation needs further study.

Influence of sodium hydroxide addition on characteristics and environmental risk of heavy metals in biochars derived from swine manure

In order to improve characteristics of biochar, especially enhance immobilization of heavy metals in biochar, swine manure was pyrolyzed at low pyrolysis temperature (300 °C, 400 °C and 500 °C) with different amounts of sodium hydroxide (NaOH) added (0.5% and 2%, W/W). Results showed that NaOH addition during pyrolysis increased the pH, EC, ash content, yield rate, aromaticity and hydrophily, but did not increase surface area and porosity of resultant biochars. The addition of NaOH promoted the transformation of the mobile fraction of Cu, Zn and Cd into the oxidizable fraction. With respect to Cr and Pb, the oxidizable and residual fractions were increased slightly by the presence of NaOH. Meanwhile, adding NaOH could reduce the leachability and ecological risks of heavy metals in biochars. Our study suggested that NaOH-assisted pyrolysis of swine manure was an effective disposal approach for the immobilization of heavy metals.

Activation or sequestration of heavy metals during hydrothermal process of swine manure: Interactions among metal species and particulates

Whether the heavy metals in solid biomass is activated or sequestrated during hydrothermal process (HTP) is still debated. Herein, the speciation of light and heavy metals during HTP of swine manure (SM) was investigated to reveal the interactions among these metal species and specific particulates. With increasing temperature, most of exchangeable species and that bound to carbonates were released to liquid phase via ion exchange and acid dissolution. Dissociation of Fe-Mn oxides rarely happened in spite of anoxic atmosphere formed during HTP. Substantial decomposition of lignocelluloses hardly caused significant liberation of fraction bound to organics. Instead, a part of fraction in liquid phase was re-captured by new oxygen-containing functional groups on solid product surface to form fraction bound to organics. Donpeacorite, butschliite and iwakiite were formed as primary minerals, resulting in increase of residual fraction of all metals except for K and Mg at 250 °C. In summary, Cu, Zn and Pb species evolution was affected by speciation of K, Ca, Mg, Fe and Mn significantly. Cu, Zn, Pb, Fe, Mn and Ca were sequestrated whereas K and Mg were activated with enhancing temperature during HTP in terms of their mobility factors.

Effect of pyrolysis temperature on characteristics, chemical speciation and environmental risk of Cr, Mn, Cu, and Zn in biochars derived from pig manure

The comprehensive analysis of environmental risk for heavy metals in pig manure was essential for optimization of pyrolysis conditions and scientific utilization of pig manure biochars as soil amendment. However, in previous studies, the selected pyrolysis temperature points were limited and temperature interval was large, it's was difficult to accurately verify the effect of pyrolysis temperature on chemical speciation and environmental risk of heavy metals. Therefore, in this study, pig manure was pyrolyzed at 300-700 °C with a small interval of 50 °C to study the effect of pyrolysis temperature on characteristics and environmental risk of Cr, Mn, Cu and Zn in pig manure biochar. Results indicated that the characteristics of biochars (>500 °C) were relatively stable. The biochar obtained at 700 °C exhibited the largest surface area (8.28 m² g^-1) and pore volume (25.17 m³ kg^-1), secondly is the biochar derived at 500 °C. The total percentages of exchangeable and acid fraction and reducible fraction decreased from 16.98% to 9.43% for Cr, 85.60% to 65.55% for Mn, 57.26% to 10.61% for Cu, 37.90% to 13.78% for Zn, respectively, suggesting that exchangeable and acid fraction and reducible fraction of Cr, Mn, Cu and Zn in pig manure were transformed into oxidizable and residual fractions after pyrolysis. The leaching rates, risk assessment code and potential ecological risk index values significantly decreased after pyrolysis and presented lower value at 500 and 700 °C. Biochars derived at 300-700 °C conditions posed no phytotoxicity with germination index >80%. Correlation analyses revealed that larger surface area, pore volume and pH values of biochars may help to immobilize heavy metals and reduce bioavailability. These findings demonstrated that bioavailability and toxicity of Cr, Mn, Cu and Zn in pig manure biochar were greatly reduced after pyrolysis and the optimum temperature was 500 °C considering energy cost.

A further inquiry into co-pyrolysis of straws with manures for heavy metal immobilization in manure-derived biochars

Co-pyrolysis of straws with manures has been found effective to mitigate heavy metal risks in manure-derived biochars. This study further investigated co-pyrolysis strategy on the levels, species and risks of metals (Cu, Zn, Cr, Ni, Pb, and Cd) carried by manure-based biochars through co-pyrolyzing swine manure (SM) and corn straw (CS) with different mixture ratios (1:0, 0:1, 3:1, 1:1, and 1:3, w/w) at 300 ℃, 500 ℃ and 700 ℃. The total heavy metals in SM biochars were significantly reduced by CS addition except when SM/CS ratio was 3:1 at 300 ℃. Notably, CS addition increased stable Ni, Zn, Cu, Pb and Cd, but simultaneously mobilized part of Ni, Zn, Cu and Pb in SM biochars, especially at higher CS ratio and higher temperature. Co-pyrolysis converted less stable Cd to more stable Cd at all pyrolysis conditions, with higher CS ratio and higher temperature more effective. Overall, higher temperature (700 ℃) and higher addition ratio of CS (SM/CS 1:3) were more favorable for mitigating the potential ecological index of biochar-bearing Cd, Cu and Zn, the dominating risky contributor to SM biochars, hence more effective to mitigate the overall environmental risks of heavy metals in the derived SM biochars.

Endogenous release of metals with dissolved organic carbon from biochar: Effects of pyrolysis temperature, particle size, and solution chemistry

Metals are released from biochar (BC) in either the free or dissolved organic carbon (DOC)-combined form. The complexation of metals with DOC influences their toxicity and bioavailability in the environment. The endogenous release of metal species with heterogeneous DOC from BC is very complex; this process has been neglected and remains unaddressed in the literature to date. In this study, the yield and chemical properties of labile DOC from BC were characterized, and the release of endogenous metal/metalloid elements (K, Mg, Mn, Fe, Al, Cu, and Si) and their species from BC with various pyrolysis temperatures and particle sizes were systematically investigated under various solution chemistries. The results showed that pyrolysis temperature of BC significantly influenced the yield and composition of DOC and DOC-metal/metalloid complexes, while particle size had lower impact. The yield of BC-derived DOC significantly decreased and the components gradually changed from low-molecular weight and low-aromaticity hydrophilic humic acid-like substances to complex high-molecular weight and high-aromaticity hydrophobic substances as pyrolysis temperature increased from 200 to 700 °C. The release of total dissolved metals decreased with increasing pyrolysis temperature, while the highest total dissolved Si was released from BC with the moderate pyrolysis temperature (500 °C). The metal elements were mainly released in the DOC-combined form, while the released Si was mainly in the free form in the neutral water environment. The release of DOC increased while that of dissolved metals decreased with increasing solution pH. The release of total dissolved metals/metalloids increased but the ratio of the DOC-combined metals/metalloids decreased with increasing solution ionic strength. These results provide new insight into the understanding of endogenous metal/metalloid release from BC in the natural environment.

Chemical speciation and risk assessment of Cu and Zn in biochars derived from co-pyrolysis of pig manure with rice straw

Pig manure has been utilized as a good feedstock to produce biochar. However, the pig manure-derived biochar from intensive pig cultivation contains high levels of total and bioavailable heavy metals. In this study, the co-pyrolysis of pig manure with other biomass (e.g. rice straw) at 300-700 °C was investigated to solve the above-mentioned topic. The ammonium acetate (CH₃COONH₄), Tessier sequential extraction procedure and hydrogen peroxide were adopted to evaluate the bioavailability, chemical speciation, and potential risk of Cu and Zn in the biochars. Results showed that the addition of rice straw significantly reduced the concentrations of total, exchangeable and carbonate-associated Cu and Zn in the biochars compared to the single pig manure biochars. Co-pyrolysis of pig manure with rice straw at a mass ratio of 1:3 and at 600 °C could be most effective to reduce the concentrations of CH₃COONH₄-extractable and potential released Cu and Zn in the biochars. In conclusion, the co-pyrolysis process is a feasible management for the safe disposal of metal-polluted pig manure in an attempt to reduce the bioavailability and potential risk of heavy metals at relatively high pyrolysis temperatures.

Heavy Metal Contamination and Ecological Risk Assessment of Swine Manure Irrigated Vegetable Soils in Jiangxi Province, China

Heavy metal are often added to animal fodder and accumulate in the soils with swine manure. In this study, heavy metal (Cu, Pb, Cd, Zn, As and Cr) concentrations were determined in agricultural soils irrigated with swine manure in Jiangxi Province, China. Results showed that the average concentrations of Cu, Zn, As and Cr (32.8, 93.7, 21.3 and 75.8 mg/kg, respectively) were higher than the background values, while Pb and Cd (15.2 and 0.090 mg/kg, respectively) were lower than the background values. Contamination factors [Formula: see text] indicated that they were generally moderate for Cu, Zn, As and Cr and generally low for Pb and Cd. The contamination degree (C _d ) was calculated to be 7.5-10.0 indicating a moderate degree of contamination. The geoaccumulation index (I_geo) indicated that the soils were unpolluted with Zn, Cd and Pb, while unpolluted to moderately pollute with Cr, Cu and As. The single ecological risk factor [Formula: see text] revealed that the six heavy metals all belonged to low ecological risk. The ecological risk indices suggested that all the sampling sites were at low risk level.

Changes in structural characteristics and metal speciation for biochar exposure in typic udic ferrisols

Recent studies on biochars confirmed their potential benefits in improving soil fertility and sequestrating contaminants. However, little information on the changes in structural characteristics and metal speciation of biochars after exposure to soils is currently available. The aim of this study was to use double experimental bags to study the transformation of ozonized biochars derived from poultry manure and drying sludge (denoted PB and SB, respectively) in typic udic ferrisols. The carbon and sulfur functional groups and chemical characteristics of the biochars were determined using spectroscopic techniques, such as Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy spectroscopy, combined with chemical extractions. Metal species were characterized using Cu K-edge X-ray absorption near-edge structure and chemical sequential fractionation schemes. The results showed that the potential changes in structural characteristics and metal species of biochars in soil were highly dependent on the composition of the biochars. PB comprised highly aromatic and chemically stable C, whereas SB contained a substantial amount of easily degradable C. Oxygen-containing groups slightly increased after incubation in the soil with either 60% water holding capacity (WHC) or flooding for 3 months. Sulfur in the biochars was predominantly inorganic S. Minerals such as K, Na, Mg, and S were mobilized from the biochars, accounting for 5-55% depending on the properties and sources of the element. Both PB and SB contained high concentrations of Cu and Zn. CuO in PB dissolved within 3 months, whereas CuS in both PB and SB was partly oxidized in the soil with 60% WHC for 9 months and adsorbed to the organic phase. Zn had relatively high mobility in both biochars, resulting in its vertical migration into soils.

Contrasting effects of composting and pyrolysis on bioavailability and speciation of Cu and Zn in pig manure

The intensive and unregulated application of feed additives to commercial pig foods has resulted in high levels of Cu and Zn in pig manure. The aim of this study was to assess the impacts of composting and pyrolysis processes on the bioavailability and chemical speciation of Cu and Zn in pig manure products by single and sequential extractions, and to compare metal bioavailability in composts and biochar-amended soils in incubation experiments. Composting and pyrolysis processes can convert exchangeable and carbonate-bound Cu and Zn to organic matter and residual fractions, and significantly reduce the potential availability of metals in composts and biochars. The DTPA-Cu and Zn concentrations in soils amended with biochar BC700 were lower than in composts and soils amended with biochar BC400. It is suggested that 700 °C is the preferred pyrolysis temperature for the conversion of pig manure contaminated with heavy metals to biochar, in order to minimize environmental pollution.

Radical change of Zn speciation in pig slurry amended soil: Key role of nano-sized sulfide particles

Spreading livestock manure as fertilizer on farmlands is a widespread practice. It represents the major source of heavy metal(loid)s (HM) input in agricultural soils. Since zinc (Zn) is present at high concentrations in manure, it poses special environmental concerns related to phytotoxicity, groundwater contamination, and introduction in the food chain. Therefore, investigations on the fate and behavior of manure-borne Zn, when it enters the soil environment, are necessary to predict the environmental effects. Nevertheless, long-term field studies assessing Zn speciation in the organic waste matrix, as well as within the soil after manure application, are lacking. This study was designed to fill this gap. Using SEM-EDS and XAS analysis, we reported the following new results: (i) ZnS made up 100% of the Zn speciation in the pig slurry (the highest proportion of ZnS ever observed in organic waste); and (ii) ZnS aggregates were about 1-μm diameter (the smallest particle size ever reported in pig slurry). Moreover, the pig slurry containing ZnS was spread on the soil over an 11-year period, totaling 22 applications, and the resulting Zn speciation within the amended soil was analyzed. Surprisingly, ZnS, i.e. the only species responsible for a nearly 2-fold increase in the Zn concentration within the amended soil, was not detected in this soil. Based on SEM-EDS and XAS observations, we put forward the hypothesis that Zn in the pig slurry consisted of nano-sized ZnS crystallites that further aggregated. The low stability of ZnS nanoparticles within oxic and complex environments such as the studied soil was the key explanation for the radical change in pig slurry-borne Zn speciation after long-term amendments.