Effects of production conditions on yield and physicochemical properties of biochars produced from rice husk and oil palm empty fruit bunches

Biochar is the bio-solid material produced by pyrolysis. The biochar properties are controlled by feedstock and pyrolysis variables. In this study, the impacts of these production variables on biochar yield and physicochemical properties including pH, cation exchange capacity (CEC), total organic carbon (TOC) content, surface area, and pore volume and size were investigated. Rice husk (RH) and oil palm empty fruit bunches (EFB) were used as biomass. The biochars were produced at temperature range of 300 to 700 °C, heating rate of 3 to 10 °C/min and retention time of 1 to 3 h. The pyrolysis conditions were optimized using response surface methodology (RSM) technique to maximize the values of the responses. Analysis of variance (ANOVA) of the results demonstrated that the data fitted well to the linear and quadratic equations. Temperature was found to be the most effective parameter on the responses followed by retention time and heating rate, sequentially. CEC, TOC, surface area, and pore characteristics were evaluated as biochar properties determining their sorption potential. The optimum conditions for the maximum values of the properties were temperatures of 700 and 493.44 °C and time of 3 and 1 h for RH and EFB biochars, respectively. Heating rate at 3 °C/min was found to be the best rate for both biochars. The structure of EFB biomass was more sensitive to heating than rice husk. The biomass type and the production variables were demonstrated as the direct effective factors on biochar yield and physicochemical properties.     

Adsorption characteristics of Cu(II) from aqueous solution onto biochar derived from swine manure

The purpose of this study was to investigate adsorption characteristic of swine manure biochars pyrolyzed at 400 °C and 700 °C for the removal of Cu(II) ions from aqueous solutions. The biochars were characterized using BET surface area, Fourier transform infrared spectroscopy (FTIR), zeta potential, scanning electron microscopy/energy dispersive spectrometer (SEM–EDS), and X-ray diffraction (XRD). The adsorption of Cu(II) ions by batch method was carried out and the optimum conditions were investigated. The adsorption processes of these biochars are well described by a pseudo-second-order kinetic model, and the adsorption isotherm closely fitted the Sips model. Thermodynamic analysis suggested that the adsorption was endothermic. The maximum Cu(II) adsorption capacities of biochars derived from fresh and composted swine manure at 400 °C were 17.71 and 21.94 mg g^?1, respectively, which were higher than those at 700 °C. XRD patterns indicated that the silicate and phosphate particles within the biochars served as adsorption sites for Cu(II). The removal of Cu(II) ions from industrial effluent indicated that the fresh swine manure biochar pyrolyzed at 400 °C can be considered as an effective adsorbent.     

Modeling adsorption kinetics of trichloroethylene onto biochars derived from soybean stover and peanut shell wastes

Trichloroethylene (TCE) is one of the most hazardous organic pollutants in groundwater. Biochar produced from agricultural waste materials could serve as a novel carbonaceous adsorbent for removing organic contaminants from aqueous media. Biochars derived from pyrolysis of soybean stover at 300 °C and 700 °C (S-300 and S-700, respectively), and peanut shells at 300 °C and 700 °C (P-300 and P-700, respectively) were utilized as carbonaceous adsorbents to study batch aqueous TCE remediation kinetics. Different rate-based and diffusion-based kinetic models were adopted to understand the TCE adsorption mechanism on biochars. With an equilibrium time of 8–10 h, up to 69 % TCE was removed from water. Biochars produced at 700 °C were more effective than those produced at 300 °C. The P-700 and S-700 had lower molar H/C and O/C versus P-300 and S-300 resulting in high aromaticity and low polarity accompanying with high surface area and high adsorption capacity. The pseudo-second order and intraparticle diffusion models were well fitted to the kinetic data, thereby, indicating that chemisorption and pore diffusion were the dominating mechanisms of TCE adsorption onto biochars.     

Effect of wheat and rice straw biochars on pyrazosulfuron-ethyl sorption and persistence in a sandy loam soil

The objective of this research was to investigate the effect of wheat and rice biochars on pyrazosulfuron-ethyl sorption in a sandy loam soil. Pyrazosulfuron-ethyl was poorly sorbed in the soil (3.5–8.6%) but biochar amendment increased the herbicide adsorption, and the effect varied with the nature of the feedstock and pyrolysis temperature. Biochars prepared at 600°C were more effective in adsorbing pyrazosulfuron-ethyl than biochars prepared at 400°C. Rice biochars were better than wheat biochars, and higher herbicide adsorption was attributed to the biochar surface area/porosity. The Freundlich constant 1/n suggested nonlinear isotherms, and nonlinearlity increased with increase in the level of biochar amendment. Desorption results suggested sorption of pyrazosulfuron-ethyl was partially irreversible, and the irreversibility increased with increase in the level of biochar. Both sorption and desorption of pyrazosulfuron-ethyl correlated well with the content of biochars. The free energy change (ΔG) indicated that the pyrazosulfuron-ethyl sorption process was exothermic, spontaneous and physical in nature. Persistence studies indicated that biochar (0.5%) amendment did not have significant effect on herbicide degradation, and its half-life values in the control, 0.5% WBC600- and RBC600-amended rice planted soils were 7, 8.6, and 10.4 days, respectively.     

Adsorption of hydrogen sulfide by biochars derived from pyrolysis of different agricultural/forestry wastes

The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different biochars derived from agricultural/forestry wastes through pyrolysis at various temperatures (100 to 500 ºC) were investigated. In this study, the H₂S breakthrough capacity was measured using a laboratory-characterized using pH and Fourier transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface. Certain threshold ranges of the pyrolysis temperature (from 100 to 500 ºC) and pH of the surface are presented. It also concluded that the sorption capacity (for removing H₂S) of rice hull-derived biochar is the largest in three biochars (camphor-derived biochar, rice hull-derived biochar, and bamboo-derived biochar). These observations will be helpful in designing biochar as engineered sorbents for the removal of H₂S.Implications: This paper focuses on the adsorption of hydrogen sulfide (H₂S) by biochars derived from wastes. The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different boichars derived from agricultural/forestry wastes through pyrolysis at various temperatures were investigated. In this study, the H₂S breakthrough capacity was measured using laboratory characterization with pH and Fourier-transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface.     

Kinetics and the mass transfer mechanism of hydrogen sulfide removal by biochar derived from rice hull

The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperature has great influence on the adsorption of H₂S. At the different pyrolysis temperature, the H₂S removal efficiency of rice hull-derived biochar was different. The adsorption capacities of biochar were 2.09 mg·g^–1, 2.65 mg·g^–1, 16.30 mg·g^–1, 20.80 mg·g^–1, and 382.70 mg·g^–1, which their pyrolysis temperatures were 100 °C, 200 °C, 300 °C, 400 °C and 500 °C respectively. Based on the Yoon-Nelson model, it analyzed the mass transfer mechanism of hydrogen sulfide adsorption by biochar.

Implications: The paper focuses on the biochar derived from rice hull–removed hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperatures have great influence on the adsorption of H₂S. At the different pyrolysis temperatures, the H₂S removal efficiency of rice hull–derived biohar was different. The adsorption capacities of biochar were 2.09, 2.65, 16.30, 20.80, and 382.70 mg·g^?1, and their pyrolysis temperatures were 100, 200, 300, 400, and 500 °C, respectively. Based on the Yoon-Nelson model, the mass transfer mechanism of hydrogen sulfide adsorption by biochar was analyzed.     

Pyrolysis temperature influences ameliorating effects of biochars on acidic soil

The biochars were prepared from straws of canola, corn, soybean, and peanut at different temperatures of 300, 500, and 700 °C by means of oxygen-limited pyrolysis. Amelioration effects of these biochars on an acidic Ultisol were investigated with incubation experiments, and application rate of biochars was 10 g/kg. The incorporation of these biochars induced the increase in soil pH, soil exchangeable base cations, base saturation, and cation exchange capacity and the decrease in soil exchangeable acidity and exchangeable Al. The ameliorating effects of biochars on acidic soil increased with increase in their pyrolysis temperature. The contribution of oxygen-containing functional groups on the biochars to their ameliorating effects on the acidic soil decreased with the rise in pyrolysis temperature, while the contribution from carbonates in the biochars changed oppositely. The incorporation of the biochars led to the decrease in soil reactive Al extracted by 0.5 mol/L CuCl₂, and the content of reactive Al was decreased with the increase in pyrolysis temperature of incorporated biochars. The biochars generated at 300 °C increased soil organically complexed Al due to ample quantity of oxygen-containing functional groups such as carboxylic and phenolic groups on the biochars, while the biochars generated at 500 and 700 °C accelerated the transformation of soil exchangeable Al to hydroxyl-Al polymers due to hydrolysis of Al at higher pH. Therefore, the crop straw-derived biochars can be used as amendments for acidic soils and the biochars generated at relatively high temperature have great ameliorating effects on the soils.     

Value of biochars from Miscanthus x giganteus cultivated on contaminated soils to decrease the availability of metals in multicontaminated aqueous solutions

The objective of this study was to evaluate the sorption efficiency of eight biochars, made from Miscanthus x giganteus cultivated on contaminated agricultural soil, in aqueous solutions contaminated with metals alone or mixed with polycyclic aromatic hydrocarbons. These biochars were produced in different pyrolysis conditions (temperature, 400/600 °C; heating rate, 5/10 °C min⁻¹; duration, 45/90 min) and compared with an uncontaminated commercialized biochar made of wood. The physicochemical characterization of the Miscanthus biochars confirmed the impact of the pyrolysis on the biochar parameters with substantial differences between the biochars in terms of pH, cation exchange capacity, and specific surface area. The sorption experiment showed higher sorption efficiency of Cd, Pb, and Zn for the Miscanthus biochars produced at 600 °C compared with the biochars produced at 400 °C when the aqueous solutions were mono- or multicontaminated. Furthermore, the desorption study showed that the sorption process was largely irreversible. Therefore, the high sorption capacity of Miscanthus biochars and the low sorption reversibility confirmed that these biochars are a suitable sorbent for metals.

     

Effectiveness and mechanisms of hydrogen sulfide adsorption by camphor-derived biochar

The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on a biochar through pyrolysis at various temperatures (100 to 500°C) were investigated. The biochar used in the current study was derived from the camphor tree (Cinnamomum camphora). The samples were ground and sieved to produce particle sizes of 0.4 mm to 1.25 mm, 0.3 mm to 0.4 mm, and <0.3 mm. The H₂S breakthrough capacity was measured using a laboratory-designed test. The surface properties of the biochar were characterized using pH and Fourier-transform infrared spectroscopy (FTIR) analysis. The results obtained demonstrate that all camphor-derived biochars were effective in H₂S sorption. Certain threshold ranges of the pyrolysis temperature and surface pH were observed, which, when exceeded, have dramatic effects on the H₂S adsorption capacity. The sorption capacity ranged from 1.2 mg/g to 121.4 mg/g. The biochar with 0.3 mm to 0.4 mm particle size possesses a maximum sorption capacity at 400°C. The pH and FTIR analysis results showed that carboxylic and hydroxide radical groups were responsible for H₂S sorption. These observations will be helpful in designing biochar as engineered sorbents for the removal of H₂S.

Implications: This paper studies the potential of biochar derived by camphor to adsorb hydrogen sulfide at environmentally sustainable temperatures. The different sizes of the biochars and the different temperatures of pyrolysis for the camphor particle have a great impact on adsorption of hydrogen sulfide.     

Properties of biochars from conventional and alternative feedstocks and their suitability for metal immobilization in industrial soil

In contaminated soils, excessive concentrations of metals and their high mobility pose a serious environmental risk. A suitable soil amendment can minimize the negative effect of metals in soil. This study investigated the effect of different biochars on metal (Cu, Pb, Zn) immobilization in industrial soil. Biochars produced at 300 and 600 °C from conventional (MS, maize silage; WP, wooden pellets) and alternative (SC, sewage sludge compost; DR, digestate residue) feedstocks were used as soil amendments at a dosage of 10 % (w/w). The type of feedstock and pyrolysis temperature affected the properties of the biochars and their ability to immobilize metal in soil. Compared to production at 300 °C, all biochars produced at 600 °C had higher pH (6.2–10.7), content of ash (7.2–69.0 %) and fixed carbon (21.1–56.7 %), but lower content of volatile matter (9.7–37.2 %). All biochars except DR biochar had lower dissolved organic carbon (DOC) content (1.4–2.3 g C/L) when made at 600 °C. Only MS and SC biochars had higher cation exchange capacity (25.2 and 44.7 cmol/kg, respectively) after charring at 600 °C. All biochars contained low concentrations of Cd, Cu, Ni, Pb and Zn; Cd was volatilized to the greatest extent during pyrolysis. Based on FTIR analysis and molar ratios of H/C and O/C, biochars had a greater degree of carbonization and aromaticity after charring at 600 °C. The efficiency of the biochars in metal immobilization depended mainly on their pH, ash content, and concentration of DOC. SC and DR biochars were more effective for Cu and Zn immobilization than MS and WP biochars, which makes them attractive options for large-scale soil amendment.     

Nanoporous activated carbon fluidized bed catalytic oxidations of aqueous o, p and m-cresols: kinetic and thermodynamic studies

Nanoporous activated carbon prepared from rice husk through precarbonisation at 400 °C and phosphoric acid activation at 800 °C was used as fluidized bed in Fenton oxidation of the o, p and m-cresols in aqueous solution. The efficiencies of homogeneous Fenton oxidation, fluidized Fenton oxidation and aerobic biological oxidation systems for the removal of o, p and m-cresols in aqueous solution have been compared. The kinetic constants and the thermodynamic parameters for the homogeneous Fenton, heterogeneous Fenton and aerobic biological oxidations of o, p and m-cresols in synthetic wastewater were determined. The degradation of cresols in synthetic wastewater was confirmed using FT-IR, ¹H-NMR and UV–visible spectroscopy.     

Characterization of contaminants and evaluation of the suitability for land application of maize and sludge biochars

Prior to the application of biochar as an agricultural improver, attention should be paid to the potential introduction of toxicants and resulting unintended impacts on the environment. In the present study, the concentrations of polycyclic aromatic hydrocarbons (PAHs), heavy metals, and mineral elements were determined in maize and sludge biochars produced at 100 °C increments between 200 and 700 °C. The concentration ranges of total PAHs were 358–5,136 μg kg^?1 in maize biochars and 179–70,385 μg kg^?1 in sludge biochars. The total heavy metals were detected at the following concentrations (mg kg^?1): Cu, 20.4–56.7; Zn, 59.7–133; Pb, 1.44–3.50; Cd, <0.014; Cr, 8.08–21.4; Ni, 4.38–9.82 in maize biochars and Cu, 149–202; Zn, 735–986; Pb, 54.7–74.2; Cd, 1.06–1.38; Cr, 180–247; Ni, 41.1–56.1 in sludge biochars. The total concentrations of PAHs and heavy metals in all maize biochars and most sludge biochars were below the control standards of sludge for agricultural use in China, the USA, and Europe. The leachable Mn concentrations in sludge biochars produced at below 500 °C exceeded the groundwater or drinking water standards of these countries. Overall, all the maize biochars were acceptable for land application, but sludge biochars generated at temperatures between 200 and 500 °C were unsuitable for application as soil amendments due to their potential adverse effects on soil and groundwater quality.     

Low-cost adsorbents from bio-waste for the removal of dyes from aqueous solution

Activated carbons (ACs) were developed from bio-waste materials like rice husk and peanut shell (PS) by various physicochemical activation methods. PS char digested in nitric acid followed by treatment at 673 K resulted in high surface area up to ～585 m²/g. The novelty of the present study is the identification of oxygen functional groups formed on the surface of activated carbons by infrared and X-ray photoelectron spectroscopy and quantification by using temperature programmed decomposition (TPD). Typical TPD data indicated that each activation method may lead to varying amounts of acidic and basic functional groups on the surface of the adsorbent, which may be a crucial factor in determining the adsorption capacity. It was shown that ACs developed during the present study are good adsorbents, especially for the removal of a model textile dye methylene blue (MB) from aqueous solution. As MB is a basic dye, H₂O₂-treated rice husk showed the best adsorption capacity, which is in agreement with the acidic groups present on the surface. Removal of the dye followed Langmuir isotherm model, whereas MB adsorption on ACs followed pseudo-second-order kinetics.     

Adsorption of ammonium on biochar prepared from giant reed

Giant reed was used as precursor for making biochar in order for the adsorption of NH₄ ⁺–N from aqueous solution. And the adsorption of the product to NH₄ ⁺–N was examined. The surface features of biochar were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy/energy dispersive spectrometer (SEM-EDS), and X-ray diffraction (XRD). XRD patterns showed several peaks and correspond to the high amount of crystalline material. The crystals contain KCl, K₂O, CaO, MgO, and SiO and possess high surface area which enhances adsorption. The influence of different parameters such as initial concentration, adsorption time, pH, and ionic strength has been carried out. The adsorption could reach equilibrium through 24 h reaction and had the best adsorption amount at the solution pH values from 7 to 9. The cation has great influence on the adsorption of NH₄ ⁺–N, whereas the anion exerted a weaker effect. The adsorption followed pseudo-first-order and pseudo-second-order models. And the intraparticle diffusion and desorption studies further elucidated that the mechanism of adsorption on the product was ion exchange. The product equilibrium data was well described by the Langmuir and Freundlich model. The maximum adsorption capacities were 1.490 mg/g. Biochar derived from giant reed at 500 °C was suggested as a promising adsorbent for the removal of NH₄ ⁺–N from slightly polluted wastewater.     

Heavy metals removal from wastewaters using organic solid waste—rice husk

In this study, the removal of Cr(III) and Cu(II) from contaminated wastewaters by rice husk, as an organic solid waste, was investigated. Experiments were performed to investigate the influence of wastewater initial concentration, pH of solution, and contact time on the efficiency of Cr(III) and Cu(II) removal. The results indicated that the maximum removal of Cr(III) and Cu(II) occurred at pH 5–6 by rice husk and removal rate increased by increased pH from 1 to 6. It could be concluded that the removal efficiency was enhanced by increasing wastewater initial concentration in the first percentage of adsorption and then decreased due to saturation of rice husk particles. Also according to achieved results, calculated saturation capacity in per gram rice husk for Cr(III) and Cu(II) were 30 and 22.5 mg?g^?1, respectively. The amounts of Cr(III) and Cu(II) adsorbed increased with increase in their contact time. The rate of reaction was fast. So that 15–20 min after the start of the reaction, between 50 and 60 % of metal ions were removed. Finally, contact time of 60 min as the optimum contact time was proposed.     

Effect of magnetic field on the removal of copper from aqueous solution using activated carbon derived from rice husk

Adsorptive removal of copper by activated carbon derived from modified rice husk (ACRH) was studied in the presence and absence of magnetic field (MF). The ACRH was prepared from the normal rice husk treated by NaOH solution and subsequent pyrolysis at 450 °C in the absence of oxygen. The physicochemical properties of ACRH's were determined before and after the adsorption process to delineate the adsorption mechanism. The BET analysis confirmed that the fabricated ACRH has a specific surface area of 8.244 m²/g with a mesopore to micropore ratio of 0.974. It was observed that the micropore structure gradually replaced the mesopores, and the surface area of the micropore increased (from 0.9219 to 4.1764 m²/g), and the pore diameter was also decreased from 180.381 to 46.249 Å after pyrolysis. The CHNO/S test result reveals that the carbon content was increased from 42 to 67.8% in the ACRH after pyrolysis. The batch sorption studies were performed by varying the initial adsorbate concentration, temperature, agitation speed, pH, adsorbent dose and contact time for magnetic and non-magnetic conditions to analyze the effect of the magnetic field. The univariate studies show that the maximum experimental adsorption capacity was 4.522 mg/g and 3.855 mg/g, respectively, for these two conditions (representing the magnetic impact) at 25 °C with an adsorbent dose of 2 g/L and an agitation speed of 150 rpm. It was also observed that the removal efficiency was 94.55% and 77.96% (magnetic and non-magnetic condition) at pH 7 with a concentration of 10 mg/L in 2 h. The test result on the impact of exposure time on the magnetic field suggested that the magnetic memory influenced the removal efficiency; after 40 to 60 min, the maximum removal efficiency was achieved, around 80 to 90%. The pseudo-second-order kinetic model was best fitted with the experimental data with a rate constant as 0.1749 and 0.1006 g/mg/min for these two conditions. The Temkin model delineates the adsorption isotherm suggesting the heat generated during the adsorption process is linearly abate with the coverage of the surface area of the adsorbent. The thermodynamic model confirms that the copper adsorption is spontaneous (ΔG = ? 3.91 kJ/mol and ? 6.02 kJ/mol), wherein the negative enthalpy value (ΔH = ? 36.74 kJ/mol and ? 25.74 kJ/mol) suggested that the process is exothermic irrespective of magnetic interference. The significant enhancement of copper removal was observed by incorporating the magnetic field, showing an increase in sorption capacity by 17.48% and a reduction of reaction time by 88.12%.

     

Efficacy of biochar in removal of organic pesticide,Bentazone from watershed systems

Abstract

Bentazone is one of the toxic insecticides used to control forest tent caterpillar moths, boll weevils, gypsy moths, and other types of moths in various field crops. We report the efficacy of biochar prepared from the Azardirachta Indica waste biomass as adsorbent for removal of Bentazone. Biochar material was prepared by pyrolysis process under limited oxygen conditions. Biochar material was characterized by proximate and ultimate analysis, SEM analysis, FTIR analysis and TG/DTA analyses. The Bentazone adsorption capacity by biochar from aqueous solutions was assessed. Effect of time, adsorbent dosage, insecticide concentration and pH on the adsorption characteristics of the biochar were evaluated. Adsorption parameters were obtained at equilibrium contact time of 150?min, with biochar dosage of 0.5?g at pH 8. From the optimization studies, desirability of 0.952 was obtained with response (adsorption uptake) of 79.40?mg/g, for initial concentration of insecticide (50?mg/L), adsorbent dosage (0.448?g), time 30.0?min and pH 2. The adsorption isotherm data for the removal of Bentazone fitted well with the Freundlich isotherm. This study indicates that the biochar produced from the bark of Azardirachta Indica biomass could be employed as a potential adsorbent for removal of synthetic organic pollutants from the water streams.     

Artificial neural network (ANN) modeling of adsorption of methylene blue by NaOH-modified rice husk in a fixed-bed column system

In this study, rice husk was modified with NaOH and used as adsorbent for dynamic adsorption of methylene blue (MB) from aqueous solutions. Continuous removal of MB from aqueous solutions was studied in a laboratory scale fixed-bed column packed with NaOH-modified rice husk (NMRH). Effect of different flow rates and bed heights on the column breakthrough performance was investigated. In order to determine the most suitable model for describing the adsorption kinetics of MB in the fixed-bed column system, the bed depth service time (BDST) model as well as the Thomas model was fitted to the experimental data. An artificial neural network (ANN)-based model was also developed for describing the dynamic dye adsorption process. An extensive error analysis was carried out between experimental data and data predicted by the models by using the following error functions: correlation coefficient (R ²), average relative error, sum of the absolute error and Chi-square statistic test (χ ²). Results show that with increasing bed height and decreasing flow rate, the breakthrough time was delayed. All the error functions yielded minimum values for the ANN model than the traditional models (BDST and Thomas), suggesting that the ANN model is the most suitable model to describe the fixed-bed adsorption of MB by NMRH. It is also more rational and reliable to interpret dynamic dye adsorption data through a process of ANN architecture.     

Removal and Destruction of Organic Contaminants in Water Using Adsorption,Steam Regeneration,and Photocatalytic Oxidation: A Pilot-Scale Study

ABSTRACT

The overall objective of this pilot-scale study is to investigate the technical feasibility of the removal and destruction of organic contaminants in water using adsorption and photocatalytic oxidation. The process consists of two consecutive operational steps: (1) removal of organic contaminants using fixed-bed adsorption; and (2) regeneration of spent adsorbent using photocatalysis or steam, followed by decontamination of steam condensate using photocatalysis. The pilot-scale study was conducted to evaluate these options at a water treatment plant in Wausau (Wisconsin) for treatment of groundwater contaminated with tetrachloroethene (PCE), trichloroethene (TCE), cis-dichloroethene (cis-DCE), toluene, ethylbenzene (EB), and xylenes. The adsorbents used were F-400 GAC and Ambersorb 563.

In the first treatment strategy, the adsorbents were impregnated with photocatalyst and used for the removal of aqueous organics. The spent adsorbents were then exposed to ultraviolet light to achieve photocatalytic regeneration. Regeneration of adsorbents using photocatalysis was observed to be not effective, probably because the impregnated photocatalyst was fouled by background organic matter present in the groundwater matrix.

In the second treatment strategy, the spent adsorbents were regenerated using steam, followed by cleanup of steam condensate using photocatalysis. Four cycles of adsorption and three cycles of steam regeneration were performed. Ambersorb 563 adsorbent was successfully regenerated using saturated steam at 160 °C within 20 hours. The steam condensate was treated using fixed-bed photo-catalysis using 1% Pt-TiO₂ photocatalyst supported on silica gel. After 35 minutes of empty bed contact time, more than 95% removal of TCE, cis-DCE, toluene, EB, and xylenes was achieved, and more than 75% removal of PCE was observed.

In the case of activated carbon adsorbent, steam regeneration was not effective, and a significant loss in adsorbent capacity was observed.     

Qualitative analysis of volatile organic compounds on biochar

Qualitative identification of sorbed volatile organic compounds (VOCs) on biochar was conducted by headspace thermal desorption coupled to capillary gas chromatographic-mass spectrometry. VOCs may have a mechanistic role influencing plant and microbial responses to biochar amendments, since VOCs can directly inhibit/stimulate microbial and plant processes. Over 70 biochars encompassing a variety of parent feedstocks and manufacturing processes were evaluated and were observed to possess diverse sorbed VOC composition. There were over 140 individual chemical compounds thermally desorbed from some biochars, with hydrothermal carbonization (HTC) and fast pyrolysis biochars typically possessing the greatest number of sorbed volatiles. In contrast, gasification, thermal or chemical processed biochars, soil kiln mound, and open pit biochars possessed low to non-detectable levels of VOCs. Slow pyrolysis biochars were highly variable in terms of their sorbed VOC content. There were no clear feedstock dependencies to the sorbed VOC composition, suggesting a stronger linkage with biochar production conditions coupled to post-production handling and processing. Lower pyrolytic temperatures (?350 °C) produced biochars with sorbed VOCs consisting of short carbon chain aldehydes, furans and ketones; elevated temperature biochars (>350 °C) typically were dominated by sorbed aromatic compounds and longer carbon chain hydrocarbons. The presence of oxygen during pyrolysis also reduced sorbed VOCs. These compositional results suggest that sorbed VOCs are highly variable and that their chemical dissimilarity could play a role in the wide variety of plant and soil microbial responses to biochar soil amendment noted in the literature. This variability in VOC composition may argue for VOC characterization before land application to predict possible agroecosystem effects.