Pyrolysis Of Sawdust Research Articles

Microwave pyrolysis of agricultural waste: Influence of catalysts, absorbers, particle size and blending components

The paper presents the results of experimental study of thermochemical conversion, phase transformations and chemical reactions during microwave pyrolysis of biomass (sawdust, straw, nutshells, rice husk, etc.). For the first time, the characteristics of the microwave co-pyrolysis of agricultural waste have been analyzed. The experiments aimed to register the yield of the main pyrolysis products (gas, char and bio-oil) by varying the following factors: type of biomass, particle size, type of absorber/catalyst, and composition of mixtures. The biomass particle size of 800 µm was optimal in terms of pyrolysis gas yield and quality. Pyrolysis of sawdust and straw had the maximum yield of combustible gas components in relation to CO2. The volumetric concentrations of CO, CH4, and H2 for these types of biomass were 20–70% higher than those for wheat bran, rice husk, and nut shell. Among the low-grade catalysts studied, carbon residue and charcoal were the most efficient in terms of maximizing combustible gas yield and reducing CO2. These catalysts reduced the bio-oil yield by a factor of 1.2 and increased the yield of combustible gases by a factor of 1.3. Pyrolysis of mixtures showed significant synergy, both positive and negative. The minimum yield of gas with the worst quality was typical for the mixture “rice husk 50%, sawdust 50%”. The maximum positive synergistic effects were recorded for the composition “rice husk 33%, sawdust 33%, and bran 33%”. The combination of these components increased the yield of CO, CH4 and H2 by 5–24%, 8–53% and 2–45%, respectively, compared to other mixtures. Thus, microwave co-pyrolysis creates great scope for the conversion of those components that do not provide the required gas characteristics during individual pyrolysis. Pyrolysis of mixtures contributes to the utilization of a large amount of plant waste while maintaining the quality of the end products.

Catalytic pyrolysis of pine sawdust over activated carbon-supported Fe for phenol-rich bio-oil

In this study, catalytic pyrolysis was used to decompose pine sawdust into platform chemicals. A strategy to produce valuable alkylphenol compounds through catalytic pyrolysis was proposed by introducing surface active groups (metal iron species and oxygen-containing groups) to strengthen biochar-based catalyst. The results showed that the multiple active sites jointly promoted the further reaction of the pyrolytic intermediates absorbed on the Fe-activated carbon catalyst during the catalytic pyrolysis, and the furans and ketones, etc., were all converted into phenolic compounds under the action of fresh Fe-activated carbon catalyst (AC-Fe-1). After the fifth recycling of the catalyst (AC-Fe-5), the catalytic performance of deactivated catalyst could be well recovered by the simple regeneration treatment, showing a good selectivity for phenol production (AC-Fe-CO2, 87 %). Compared with non-catalytic pyrolysis, the relative content of phenolic substances generated by Fe-activated carbon in the catalytic pyrolysis increased from 15.42 % to more than 90 %, mainly methyl phenolics such as phenol, 2-methylphenol and 3-methylphenol. By contrast, the deactivation of Fe-activated carbon catalyst was not significant and the selectivity to phenol increased to 73.62 %─80.01 %, while the original activated carbon (without adding iron species) was seriously deactivated and the selectivity to phenol decreased by 38.26 %.

Influence of torrefaction with microwave and furnace heating on pyrolysis of poplar sawdust

Microwave heating is different from furnace heating in terms of heat transfer direction and heating mechanism. The torrefaction with microwave or furnace heating might further impact evolution of the pyrolytic products in further pyrolysis. This was investigated herein via thermal pretreatment of sawdust at 150 to 250 °C and the subsequent pyrolysis at 600 °C. The results showed that the microwave pretreatment led to more pronounced pyrolysis at 200/250 °C, which enhanced aromatic degree of semi-char and created difficulty for its further cracking in pyrolysis at 600 °C but not affected gasification. This led to the formation of more biochar and much more gases but less bio-oil with less heavy components than that from furnace heating plus pyrolysis. Additionally, the microwave pretreatment could enhance deoxygenation but the enhanced aromatic degree of the semi-char created difficulty for creating micropores and development of the pore structures (176.2 m2g−1 with 67.3% micropores from microwave pretreatment versus 441.1 m2g−1 with 78.5% micropores from furnace pretreatment). The characterization of the pyrolysis of semi-char with in-situ IR technique confirmed that the microwave pretreatment substantially removed the aliphatic structures and made the biochar with more fragmented morphology.

Sequential pyrolysis of spirulina and sawdust: Interactions of volatiles from upper-bed feedstock to lower-bed biochar

Co-pyrolysis of mixed feedstocks is a common practice in research and industrial operation. Cross-interactions of volatiles of varied origins have been well documented in many existing studies. However, it remains a challenge to understand the transfer of volatiles from feedstock A to biochar of feedstock B during co-pyrolysis, due to the complexity of the reaction network. To examine this issue, sequential pyrolysis of spirulina and sawdust with up-down configured dual beds was conducted to probe specifically how volatiles from one feedstock could impact the biochar from another feedstock. The results confirmed the interactions of volatiles with biochar of the other feedstock, which diminished oxygen/nitrogen-containing compounds and heavy π-conjugated components in the bio-oils. Carbonaceous deposits were also observed, enhancing yields of biochar but at the expense of bio-oil. The transfer of inorganic species and N-containing species from spirulina to sawdust-biochar as well as the carbon-rich coating of the spirulina-biochar from the deposition of sawdust volatiles were observed, making the biochars more hydrophobic. Additionally, these interactions also remarkably enhanced the thermal stability of the sawdust-biochar. The transfer of organics and inorganics during sequential pyrolysis also resulted in the coarse surface of biochars dotted with many small particulate matters with an average particle size of 2.0–3.8 µm.

Microwave-assisted pyrolysis of pine sawdust: Process modelling, performance optimization and economic evaluation for bioenergy recovery

This study aims at optimizing the process conditions to extract maximum yields of bio-oil from pine sawdust using microwave-assisted pyrolysis (MAP). Aspen Plus® V11 was used to model the thermochemical conversion of pine sawdust to pyrolysis products, and response surface methodology (RSM) based on a central composite design (CCD) was employed in the optimization of the process parameters. The mutual effects of pyrolysis temperature and reactor pressure on the product distribution were investigated. The findings have shown that the optimal operating conditions for producing the highest amount of bio-oil (65.8 wt%) were achieved at 550 °C and 1 atm. The product distribution of the simulated model was more significantly influenced by linear and quadratic terms of the reaction temperature. In addition, a high determination coefficient (R2 = 0.9883) was obtained for the developed quadratic model. A set of three published experimental results acquired under circumstances comparable to the simulations' operating limitations were used to further validate the simulation results. The process’s economic viability was assessed in order to establish the bio-oil minimum selling price (MSP). A MSP of $1.14/L of liquid bio-oil was evaluated. An economic sensitivity analysis has shown that the annual fuel yield, required rate of return, annual income tax, annual operating costs and initial capital investment have a substantial impact on the MSP of bio-oil. It was inferred that using the optimized process parameters may improve the process' competitiveness on an industrial scale due to its better product yields and improved sustainability in biorefineries, as well as assure waste reduction.

Aromatics production from segmented co-pyrolysis of poplar sawdust and high-density polyethylene: Enhancing the synergistic effects

Catalytic co-pyrolysis of biomass and plastic waste is a promising approach for producing renewable biofuels and value-added chemicals. However, because of their different pyrolysis behaviors, the synergy between biomass and plastic is limited, and low-yield aromatics are produced. Herein, a modified segmented catalytic co-pyrolysis technology was proposed, and the effects of pyrolysis parameters were studied in detail to enhance the synergistic effect between feedstocks. For the biomass section (segment 1), catalytic fast pyrolysis (CFP) of poplar sawdust was conducted, and results showed that employing 15 wt% MgCl2 at 500 °C facilitated the production of furans. For the plastic section (segment 2), CFP of high-density polyethylene (HDPE) were performed. It was showed that instead of Y and beta zeolites, the utilization of ZSM-5 as a pyrolysis catalyst with a loading of ZSM-5/HDPE = 1.0, and a temperature of 600 °C was beneficial for the production of short-chain olefins. For the segmented co-pyrolysis of poplar sawdust and HDPE (segment 1 + segment 2), the biomass-to-plastic ratio was crucial in aromatics production. A ratio of 1:1 was found to be most effective in producing MAHs (54.8 area%), which was ∼3.9 or 1.6 times that for the separate CFP of biomass or HDPE. This was also consistent with its higher enhancement factor, confirming that the synergy between poplar sawdust and HDPE was dramatically enhanced. Finally, a segmented catalytic co-pyrolysis reaction pathway was proposed.

Синтез карбида бора электродуговым методом в открытой воздушной среде из углерода различного происхождения

The paper presents the results of experimental studies on the implementation of electric arc synthesis of boron carbide using carbon with different morphology and origin as a feedstock: carbon fibers, flake graphite, carbon obtained by pyrolysis of plant waste, namely, pine sawdust and cedar nuts husks. A feature of the electric arc method used is its implementation using an original plasma reactor using atmospheric air as a working gas medium. Oxidation of feedstock and synthesis products in the working cycle of the reactor is prevented due to the generation of CO and CO2 gases in the reaction zone. The possibility of obtaining a material containing micron and submicron boron carbide crystals in a graphite matrix has been experimentally shown. Also, the paper presents information about the features of the oxidation processes of the obtained materials in comparison with commercial samples of boron carbide.

Synthesis of boron carbide by the electric arc method in open air from carbon of various origins

The paper presents the results of experimental studies on the implementation of electric arc synthesis of boron carbide using carbon with different morphology and origin as a feedstock: carbon fibers, flake graphite, carbon obtained by pyrolysis of plant waste, namely, pine sawdust and cedar nuts husks. A feature of the electric arc method used is its implementation using an original plasma reactor using atmospheric air as a working gas medium. Oxidation of feedstock and synthesis products in the working cycle of the reactor is prevented due to the generation of CO and CO2 gases in the reaction zone. The possibility of obtaining a material containing micron and submicron boron carbide crystals in a graphite matrix has been experimentally shown. Also, the paper presents information about the features of the oxidation processes of the obtained materials in comparison with commercial samples of boron carbide. Keywords: boron carbide, electric arc synthesis, carbon fibers, flake graphite, carbon of plant origin.

Pyrolysis of low-value waste sawdust over low-cost catalysts: physicochemical characterization of pyrolytic oil and value-added biochar

The present work deals with an experimental investigation into the generation and characterization of pyrolytic oil and biochar from Sal wood sawdust (SW). The pyrolysis experiment was performed in a semi-batch reactor at 500 oC and 80 oC/min heating rate with CaO, CuO, and Al2O3 catalysts. Further, the pyrolytic oil and biochar were investigated using different analyses, including proximate analysis, elemental analysis, thermal stability, GC-MS, FTIR, field emission scanning electron microscopy, electrical conductivity analysis, higher heating value (HHV), zeta potential analysis, and ash content analysis. Pyrolysis results revealed that compared to thermal pyrolysis (46.02 wt%), the pyrolytic oil yield was improved by catalytic pyrolysis with CaO and CuO (50.02 and 48.23 wt%, respectively). Further, the characterization of pyrolytic oil revealed that the loading of catalysts considerably improved the oil's properties by lowering its viscosity (69.50 to 22 cSt), ash content (0.26 to 0.11 wt%), and oxygen content (28.32 to16.60 %) while raising its acidity (4.2 to 9.6), heating value (25.66 to 36.09 MJ/kg), and carbon content (61.79 to 74.28%). According to the FTIR analysis, the pyrolytic oil contained hydrocarbons, phenols, aromatics, alcohols, and oxygenated compounds. Additionally, the GC-MS analysis showed that catalysts significantly reduced oxygenated fractions, phenols (20.23 to 15.26%), acids (12.23 to 6.56%), and increased hydrocarbons (12 to 16 wt%). Additionally, the results of the biochar analysis demonstrated that SW biochar was appropriate for a range of industrial applications, including in catalysts, supercapacitors, fuel cells, and bio-composite materials.

Catalytic Pyrolysis of Sawdust with Desulfurized Fly Ash for Pyrolysis Gas Upgrading

In this study, the catalytic effects of desulfurized fly ash (DFA) on the gaseous products of sawdust (SD) pyrolysis were investigated in a tubular furnace. The results indicated that DFA catalyzed the process of SD decomposition to improve the hydrogen content and the calorific value of pyrolysis gas. As to its effect on pyrolysis products, DFA increased the non-oxide content of CH4, C3H4, and H2 in pyrolysis gas by 1.4-, 1.8-, and 2.3-fold, respectively. Meanwhile, the catalytic effect of DFA reduced the CO and CO2 yields during DFA/SD pyrolysis. Based on the model compound method, CaSO3 and Ca(OH)2 in DFA was proved to have quite different catalytic effects on pyrolysis gas components. Ca(OH)2 accelerated the formation of CH4 and H2 through the cracking of methoxyl during lignin and cellulose degradation, while CaSO3 favored the generation of CO and CO2 due to the carbonyl and carboxyl of lignin in SD. CaSO3 also catalyzed SD pyrolysis to promote the C3H4 yield in pyrolysis gas. Overall, the catalytic pyrolysis of SD with DFA yielded negative-carbon emission, which upgraded the quality of the pyrolysis gas.

Monophenols recovery by catalytic pyrolysis of waste sawdust over activated biochar from the brown macroalgae Hizikia fusiformis: Mechanism and life-cycle assessment

As an indispensable by-product of thermal conversion process, biochar can be modified to achieve outstanding performance in many applications. In particular, it has favorable properties for catalytic pyrolysis due to its advantageous porous structure and abundant surface functional groups. In the present study, the ecological impact of activated biochar obtained from phaeophyte Hizikia fusiformis was evaluated using life cycle assessment (LCA) approach. Subsequently, activated biochar was employed as a catalyst during pyrolysis of waste sawdust for monophenols recovery. Concretely, activated biochar was prepared from H. fusiformis in a fixed bed reactor through a two-step activation method. Results of LCA showed that employment of KOH has the highest environmental burdens in all steps for all studied impact categories. In addition, it was found that employment of KOH as an activator resulted in lower greenhouse gas emissions than other activated biochars. During catalytic pyrolysis process, the biochar-based catalyst was confirmed to facilitate the dehydration, decarbonylation, and decarboxylation reactions, resulting in more gaseous components. In addition, the content of -OH was found to decrease after catalytic process, while the content of C-O-C increased. According to GC-MS analysis, it was found that activated biochar catalyst significantly promotes the yields of monophenols (reached up to 48.99%), which were mainly ascribed to the porous structure and the surface functional groups, i.e. mesopores structure and pyridinic-N, respectively.

Efficient degradation of p-chlorophenol by N,S-codoped biochar activated perxymonosulfate

The easy preparation of low-cost, highly active, and environment-friendly carbon-based catalysts for wastewater treatment remains a challenge. In this study, we fabricated a biochar codoped with nitrogen and sulfur (NS-BC) as a low-cost and efficient catalyst for peroxymonosulfate (PMS) activation and p-chlorophenol degradation. NS-BC was synthesized by the pyrolysis of sawdust with urea and sulfur powder serving as the nitrogen source and sulfur source, respectively. Due to the large surface area and high defect degree of NS-BC, its catalysis performance for PMS (Kobs=0.8104) was better than those of single-doped (Kobs=0.4177 and Kobs=0.3132) and undoped (Kobs=0.1265) biochar, and it can completely degrade p-chlorophenol within 5 min. The main active substances in the activation process of PMS were elucidated by free radical burst experiments and electron paramagnetic resonance analysis. Superoxide radical and singlet oxygen were the main active species of the system. These catalysts achieve rapid removal of a wide range of organic contaminants over a wide pH range. This work mainly emphasizes that the use of nonmetal-doped biochar to activate PMS to degrade p-chlorophenol, thereby avoiding the environmental harm of metal leaching during catalyst degradation.

Study on the pyrolysis characteristics of sawdust catalyzed by spent FCC catalyst and blast furnace ash

Two industrial wastes, spent FCC catalyst (sFCCc) and blast furnace ash (BFA), were used as catalysts in the fast pyrolysis of sawdust, and the catalytic pyrolysis reaction characteristics of sawdust in the temperature range of 400–700 °C were explored. The results showed that both catalysts promoted the conversion from liquid products to gaseous products, and the highest gas yield was 52.60% at 700 °C catalyzed by BFA. The sFCCc had stronger deoxygenation activity at 500–600 °C, resulting in higher CO and CO2 production in gaseous products. While BFA had higher polycondensation and dehydrogenation activity at 600–700 °C, and promoted the formation of polycyclic aromatic compounds and H2. Pyrolysis oil was mainly composed of phenols. The sFCCc promoted the conversion of methoxy phenol to benzenediol. FT-IR analysis of pyrolysis oil showed that sFCCc promoted the removal of C–O and C=O, resulting in decreased acid and ester compounds and increased CO2 yield.

Staged pyrolysis of biomass to probe the evolution of fractions of bio-oil

Bio-oil is a complex mixture of organics and each group of chemicals has a varied response to pyrolysis temperatures. This was investigated via the staged pyrolysis of poplar sawdust, cellulose, and lignin by consecutively increasing temperature to 250, 350, 450, and 550 °C, respectively. The results showed that 350 °C was the boundary temperature for formation of majority of organics from sawdust and cellulose and more than half of organics from lignin. The further increase of temperature to 550 °C mainly promoted the aromatization of reaction intermediates from aliphatic components. The staged pyrolysis also facilitated the charring reactions, generating the bio-oil with more light organics including anhydrate sugars, ketones, aldehydes, and phenolics. The enhanced charring reactions promoted the carbonization reactions via deoxygenation, making biochar carbon-rich and thermally more stable. Additionally, the staged pyrolysis also impacted the morphologies and evolution of the functionalities of biochar via influencing the volatile-char interactions.

Phosphate adsorption improvement using a novel adsorbent by CaFe/LDH supported onto CO2 activated biochar.

It is imperative to remove phosphate from the aquatic system. This nutrient in excess can cause environmental problems such as eutrophication. Therefore, aiming to enhance phosphate removal, this work presents a novel adsorbent developed from the construction of Ca2+/Fe3+ layer double hydroxides (CaFe/LDH) supported onto biochar physically activated with CO2 [CaFe/biochar (CO2)]. Pristine biochar was produced from the pyrolysis of Eucalyptus saligna sawdust, activated with CO2, and then impregnated with CaFe/LDH. The CaFe/biochar (CO2) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET). The characterization confirmed a proper synthesis of the new adsorbent. Experiments were conducted in the form of batch adsorption. Results indicated that the optimum pH and adsorbent dosage were 2.15 and 0.92 g L-1, respectively. Adsorption kinetics, isotherms, and thermodynamics were also evaluated. Adsorption kinetics and isotherms were better fitted by the pseudo n order and Freundlich models, respectively. Results also indicated a better adsorption capacity (99.55 mg·g-1) at 55 °C. The thermodynamic indicators depicted that the adsorption process was favorable, spontaneous, and endothermic. Overall, CaFe/biochar (CO2) could be potentially applied for the adsorptive removal of phosphate from an aqueous solution.

Jet fuel-range hydrocarbons generation from the pyrolysis of saw dust over Fe and Mo-loaded HZSM-5(38) catalysts

In this research, we studied the catalytic pyrolysis of sawdust over monometal (1 wt% Fe or 1 wt%Mo) and bimetal (1 wt% Fe-1 wt% Mo or 0.5 wt% Fe-0.5 wt% Mo)-loaded HZSM-5(38) catalysts, synthesized via wet impregnation method, for the generation of jet fuel-range hydrocarbons. In particular, we aimed to generate jet fuel-range aromatic hydrocarbons (C8-C12) and a high amount of organic-phase bio-oil at the same time from this pyrolysis. In addition, the bimetal-loaded HZSM-5(38) catalysts (1 wt% Fe-1 wt% Mo/HZSM-5(38) and 0.5 wt% Fe-0.5 wt% Mo/HZSM-5(38)) helped achieve a higher organic phase bio-oil yield (20.74 and 17.14 wt%) compared to those under the pristine HZSM-5 (9.57 wt%) and monometal-loaded HZSM-5(38) catalysts (1 wt%Fe/HZSM-5(38) and 1 wt% Mo/HZSM-5(38)) (13.04 and 11.45 wt%, respectively). The exchange of the strong Brønsted acidity in the HZSM-5(38) support with an added metal (Mo and Fe) ion of this catalyst might have prevented excessive cracking and dehydration of the bio-oil intermediates, thereby increasing the organic-phase bio-oil yield of the pyrolysis. The coke amount of bimetal-loaded HZSM-5(38) catalyst was lower than that of monometal-loaded HZSM-5(38). Overall, the bimetal-loaded HZSM-5(38) catalysts possessed a synergistic effect leading to their high activity, generating the higher amount of jet fuel-range hydrocarbons because of the enhanced deoxygenation such as hydrodeoxygenation and dehydrogenation reactions of the pyrolysis under this catalyst.

BIOCHAR DERIVED FROM SLOW PYROLYSIS AND ITS APPLICATION AS SORBENT IN REMOVAL OF METHYLENE BLUE FROM AQUEOUS SOLUTION

In this study, biochar (BC) derived from slow pyrolysis of spruce sawdust and activated BC with HNO3 were used as sorbents to remove methylene blue (MB) dye from the aqueous solution. BC was prepared by pyrolysis at temperatures of 200, 300, 400, and 500 °C. Based on the screening results, the two BCs (BC prepared at 400 °C and BC prepared at 500 °C) exhibiting a higher percentage of dye removal were selected to investigate further the effect of factors, including contact times 15, 30, and 60 minutes and the amount of dosage – BC 0.01, 0.03, 0.05 g / 8 mL. The sorption efficiency of MB was determined by measuring the absorbance of the solutions after sorption in a UV / VIS area of 665 nm. BC prepared at 500 °C was found to perform better than BC prepared at 400 °C and activated BC by HNO3 and has more than 95 % rate of methylene dye adsorption.

Pyrolysis of sawdust coupled with steam reforming for simultaneously production of heavy organics and hydrogen

In hydrotreatment of bio-oil, it is difficult to convert the aliphatic compounds with the carbon number less than four into liquid fuel via hydrodeoxygenation. Thus, ideally, the very light organics of bio-oil could be reformed to generate hydrogen for further upgrading the heavier organics in bio-oil to biofuel or fine chemicals. In this study, the pyrolysis of poplar sawdust coupled with the simultaneously steam reforming of the bio-oil (pyro-reforming) were studied over Ni/SBA-15 catalyst at the medium temperature range from 450 to 650 °C for transforming mainly the light aliphatic compounds into H2. The results showed that the effective steam reforming of the aliphatic compounds like carboxylic acid and small aldehydes/ketones took place to remarkable extent from 550 °C, while the furans, anhydrate sugars, light phenols and heavy phenolics of fused ring structures could be largely retained in the resulting bio-oil. Coking reached the maximum with increasing temperature to 500 °C from cracking/polymerization of the volatiles. Further increase of temperature to 650 °C accelerated steam reforming and gasification of precursors of coke, shifting the morphology of coke from amorphous form to unregular carbon nanotube structures (stringed beads-like) and making the coke more aromatic and more resistant to oxidation. Nevertheless, in overall, the coke produced from 450 to 650 °C was aliphatic with low C/H ratio, low thermal stability and low crystallinity, originating from the significant contribution from the aliphatic compounds in the bio-oil for coking.

Effect of dry torrefaction pretreatment of the microwave-assisted catalytic pyrolysis of biomass using the machine learning approach

This study employs the Leave-One-Out cross-validation approach to build a machine-learning model using polynomial regression to predict pyro product yield through microwave-assisted pyrolysis of sawdust over KOH catalyst and graphite powder a susceptor. The determination of coefficient (R2) validates the developed models. All the developed models achieved a high prediction accuracy with R2 > 0.93, which signifies that the experimental values are in good agreement with the predicted one. The dependence of the catalyst loading and pretreatment temperature on dominating process parameters such as heating rate, pyrolysis temperature, susceptor thermal energy, and pyro products, namely bio-oil, biochar, and biogas, are explored. The yield of biochar is reduced; however, bio-oil and biogas are enhanced as the catalyst loading increased. On the other hand, increasing the temperature of pretreated sawdust decreased bio-oil and biogas yields while increasing biochar yields. Further, microwave conversion efficiency, and susceptor thermal energy increased with increased catalyst quantity and pretreatment temperatures of sawdust. It was observed that the average heating rate was increased by increasing the catalyst quantity while maintaining the same pyrolysis time until pretreatment temperatures of 150 °C were reached, after which the heating rate dropped due to the continuous microwave energy input to the system.

Mobility of water-soluble aerosol organic matters (WSAOMs) and their effects on soil colloid-mediated transport of heavy metal ions in saturated porous media

Water-soluble aerosol organic matters (WSAOMs) produced by biomass pyrolysis/burning can penetrate subsurface environment, and are anticipated to have a profound effect on the fate of contaminants in aquatic ecosystems. Herein, WSAOMs derived from corn straw (CS-WSAOMs) and pinewood sawdust (PW-WSAOMs) pyrolysis at 300–900 °C were utilized to investigate their mobility characteristics and impacts on the transport of heavy metal ions (i.e., Cd2+) in saturated quartz sand with or without soil colloids. This study clearly demonstrated that WSAOMs in subsurface systems exhibited high mobility, which increased as WSAOMs molecular sizes decreased and hydrogen-bond interactions between WSAOMs and sand grains declined. WSAOMs significantly improved heavy metal (i.e., Cd2+) and soil colloid-mediated Cd2+ mobility in the porous media, which stemmed from the increased binding affinities of colloids toward metal ions and the high mobility of WSAOMs. Interestingly, in terms of the mobility and colloid-facilitated transport of Cd2+, WSAOMs from higher pyrolysis temperatures exhibited enhanced effects; meanwhile, the PW-WSAOMs demonstrated stronger effects than the CS-WSAOMs. The trends were mainly attributed to the differences in the metal-binding affinities (e.g., cation-π interactions) and transport abilities of WSAOMs, as well as diverse Cd2+ adsorption capacities of colloids induced by various WSAOMs.