Hydrophobicity Of Biochar Research Articles

An investigation of drum granulation of post‐pyrolysis washed biochar

AbstractBiochar, unwashed and washed with a solution of Triton and hydrogen peroxide, was wet drum granulated using molasses binder solutions. Unwashed biochar was very hydrophobic and granulation proceeded through forming liquid marbles and layering. Washing reduced the hydrophobicity of the biochar. The effectiveness of the wash depended on the biochar source; it significantly reduced the hydrophobicity of biochar from woodchips and moderately reduced the hydrophobicity of biochar from flower digestate. Therefore, washed biochar from woodchips was granulated using a hydrophilic mechanism, while washed biochar from digestate was granulated according to a combination mechanism of liquid marbles collapsing and then coalescing. The change in granulation mechanism produced stronger and denser granules with higher yields of granules in the 1–4 mm optimal size range. Washing and then granulating biochar created a product that could be further tailored for optimal soil amendment.

Sludge Biochar Modified by B-doped and Its Adsorption Behavior and Mechanism of 1,2-DCA in Water

Sludge biochar (BC600) and B-doped sludge biochar (BBC600) were prepared with the boric acid doping modified co-pyrolysis method using municipal sludge as precursors, and the materials were structurally characterized by SEM, BET, FTIR, and Zeta potential and static contact angle to investigate the adsorption behavior, mechanism of BC600 and BBC600 on 1,2-DCA in water, and the influencing factors. The results of structural characterization showed that the B element content, specific surface area, and pore volume of biochar increased by 76%, 48%, and 30%, respectively, after the B doping modification; the effect of B doping modification on the surface charge and hydrophobicity of biochar was not significant. The results of adsorption experiments showed that the adsorption of 1,2-DCA by BBC600 was better than that by BC600 due to the larger specific surface area and higher strength of oxygen-containing functional groups of BBC600; the pseudo-first-order kinetic equation could better describe the adsorption of 1,2-DCA by BC600, and the pseudo-second-order kinetic equation could better fit the adsorption of 1,2-DCA by BBC600. The intraparticle diffusion was not the only rate-limiting step affecting the adsorption rate; the biochar material was more dispersed and stable under alkaline conditions, and its oxygen-containing functional groups were deprotonated and had enhanced electron-donating ability, which was beneficial to the adsorption of 1,2-DCA. Humic acid (HA) showed a low concentration-promoting and high concentration-inhibiting effect on the adsorption of 1,2-DCA by BC600, whereas both low and high concentrations of HA showed an inhibitory effect on the adsorption of 1,2-DCA by BBC600. The adsorption of 1,2-DCA by BC600 was inhibited by both low and high concentrations of HA, and HA competed with 1,2-DCA for adsorption; Cl-, SO42-, and NO3- all inhibited the adsorption of 1,2-DCA by biochar, and the degree of inhibition ordered from small to large was Cl-<SO42-<NO3-. The main mechanisms of 1,2-DCA adsorption by biochar were pore filling and π-π interaction.

The importance of presoaking to improve the efficiency of MgCl2-modified and non-modified biochar in the adsorption of cadmium

Investigating the effect of presoaking, as one of the most important physical factors affecting the adsorption behavior of biochar, on the adsorption of heavy metals by modified or non-modified biochar and presoaking mechanism is still an open issue. In this study, the water presoaking effect on the kinetics of cadmium (Cd) adsorption by rice husk biochar (produced at 450 °C, B1, and at 600 °C, B2) and the rice husk biochar modified with magnesium chloride (B1 modified with MgCl2, MB1, and B2 modified with MgCl2, MB2) was investigated. Furthermore, the effect of pH (2, 5, and 6), temperature (15, 25, and 35 °C), and biochar particle size (100 and 500 µm) on the kinetics of Cd adsorption was also investigated. Results revealed that the content of Cd adsorbed by the presoaked biochar was significantly higher than that by the non-presoaked biochar. The highest Cd adsorption capacity of MB2 and MB1 was 98.4 and 97.6 mg g−1, respectively, which was much better than that of B1 (7.6 mg g−1) and B2 (7.5 mg g−1). The modeling of kinetics results showed that in all cases pseudo-second-order model was well-fitted (R2>0.99) with Cd adsorption data. The results also indicated that the highest Cd adsorption values were observed at pH 6 in presoaked MB1 with size of 100 µm as well as at the temperature of 35 °C in presoaked MB2, indicating the optimum conditions for this process. The presoaking process was not affected by biochar size and pH, and the difference in adsorbed Cd content between presoaked biochars and non-presoaked ones was also similar. However, the temperature had a negative effect on presoaking. The presoaking process decreased micropores (<10 µm) in the biochars but had no effect on biochar hydrophobicity. Therefore, presoaking, which could significantly increase Cd adsorption and reduce equilibrium time by reducing the micropores of biochars, is suggested as an effective strategy for improving the efficiency of modified biochars or non-modified ones in the adsorption of contaminants (Cd) from aquatic media.

Biochar seeding properties affect struvite crystallization for soil application

Struvite crystallization is a viable approach for recovering phosphorus from phosphorus-rich solutions such as urine and wastewater. However, designing seed materials to promote crystal growth and enhance the efficiency of struvite crystallization remains an area of active research. In this study, we investigated the seeding characteristics of biochars on struvite crystallization and the impact of biochar feedstock type and production temperature on the process. Microwave-pyrolyzed biochars produced from different feedstocks and under different temperatures were examined as seeding materials for struvite crystallization from urine and the influence of biochar properties on the overall struvite yield, nutrient recovery and struvite crystal size. Sawdust biochar (lignocellulosic biomass) produced at 500 ​°C had the highest struvite yield (7.91 ​g ​L−1), phosphate (97.9%) and ammonium recovery (87.1%), and relative crystal size (85.2%) compared to the non-seeded treatment due to its higher surface area, pore volume, and hydrophobicity of the biochar. Manure pellet biochar (non-lignocellulosic biomass) produced at 500 ​°C also exhibited performance comparable to sawdust biochar produced at 500 ​°C. Increasing pyrolysis temperature increased biochar's hydrophobicity, zeta potential, electrophoretic mobility and bulk density, irrespective of the feedstock type, thereby improving the seeding process. The ash content of biochar was negatively correlated with its surface area, pore volume, and particle size, but positively correlated with biochar's bulk density and suspension stability. In conclusion, feedstock type and pyrolysis temperature significantly affected biochar properties, which interactively influenced struvite crystallization. Therefore, biochars should be carefully selected to improve their efficiency for phosphorus recovery from phosphorus-containing solutions such as urine and wastewater, with the recovered phosphorus being used for soil applications.

Influence of Technical Parameters of the Pyrolysis Process on the Surface Area, Porosity, and Hydrophobicity of Biochar from Sunflower Husk Pellet

Biochar is a product that has been of interest to many researchers in recent years. The use and positive effect of biochar depend on its properties, which in turn result primarily from the type of substrate used for production and the technical parameters of the pyrolysis process used. From the point of view of sustainable development, agricultural raw materials, such as sunflower husks, are good materials for biochar synthesis. The research aimed to determine the effect of changing the technical parameters of the pyrolysis process (i.e., temperature, heating rate, and residence time) on the properties of biochar obtained from sunflower husk pellets. The pellets were heated to 480 °C, 530 °C, and 580 °C. The applied heating rate for 480 °C was 4.00 and 7.38 °C·min−1, for 530 °C it was 4.42 and 8.15 °C·min−1 and for 580 °C it was 4.83 and 8.92 °C·min−1. Determining these properties is important due to the use of biochar, e.g., in the processes of sorption of pollutants from the water and soil environment. The technical parameters of the pyrolysis process used allowed us to obtain hydrophilic materials with porosity in the range of 10.11% to 15.43% and a specific surface area of 0.93 m2·g−1 to 2.91 m2·g−1. The hydrophilic nature of biochar makes it possible to use them in the processes of removing inorganic pollutants and polar organic pollutants. The presence of macropores in biochar may contribute to the improvement of water management in the soil and affect the assimilation of microelements by plants. The low content of heavy metals in biochar does not pose a threat to the environment.

The role of biochar particle size and hydrophobicity in improving soil hydraulic properties

AbstractThe physical properties of biochar have been shown to dramatically influence its performance as a soil amendment. This study assessed the role of biochar particle size and hydrophobicity in controlling soil water movement and retention. Softwood pellet biochar in five particle size ranges (&gt;2 mm, 2–0.5 mm, 0.5–0.25 mm, 0.25–0.063 mm and &lt;0.063 mm) was used for the experiment. These particle sizes were tested on two soil types (sandy loam and loamy sand) at four different application rates (1, 2, 4 and 8%) in the laboratory. Soil water suction at wet range and dry range were measured using the Hyprop and WP4‐T, respectively. From this, the moisture content at field capacity (fc), permanent wilting point (pwp) and plant available water (awc), were determined. Saturated hydraulic conductivity (Ksat) was measured using the KSAT device and biochar hydrophobicity was determined using the ethanol drop test method. Our results showed that biochar hydrophobicity increased with decreasing biochar particle size, leading to a reduction in its water retention capacity. The highest fc (0.087 cm−3 cm−3) and awc (0.064 cm−3 cm−3) were observed for soils amended with &gt;2 mm biochar. The soil hydraulic conductivity increased with decreasing biochar particle sizes, with the exception of &lt;0.063 mm biochar, which showed a significant (p ≤ 0.05) decrease in soil hydraulic conductivity compared to the larger particle sizes. The results clearly showed that both biochar intraporosity (pores inside biochar particles) and interporosity (pore spaces between biochar and soil particles) are important factors affecting amended soil hydraulic properties. Biochar interpores affected mainly hydraulic conductivity; both interpores and intrapores controlled soil water retention properties. Our results suggest that for a more effective increase in soil water retention of coarse soils, the use of hydrophilic biochar with high intraporosity is recommended.Highlights Biochar increases soil water retention and reduces hydraulic conductivity. Hydrophobicity of biochar increased with decreasing particle size. Coarse biochar particles increased soil water retention due to hydrophilic surfaces and increased intraporosity. Fine biochar particles decreased hydraulic conductivity due to reduced macropores.

Effects of torrefaction conditions on the hygroscopicity of biochars

Agroforestry biomass involving cedar wood (CW), polar wood (PW), corn stalk (CS) and wheat straw (WS) was torrefied in a fixed-bed reactor under the torrefaction temperature (T) of 200–300 °C and the holding time (τ) of 10–60 min to prepared straw biochars (WSC, CSC) and woody biochars (PWC and CWC). The effects of biomass species, torrefaction temperature and holding time on the hygroscopicity of biochars were investigated under constant temperature and humidity. Combined with the results of N2 adsorption/desorption and FTIR of raw biomass and its biochars, the mechanism of torrefaction conditions on the hygroscopicity of biochar was discussed. The obtained results indicated that water absorption process of biochar can be divided into two stages of initial rapid water absorption and the later slow water absorption. The equilibrium moisture content (EMC) decreases, the hygroscopicity reduction extent (HRE) increases gradually, and hydrophobicity of biochar is enhanced with increasing torrefaction temperature. However, too high torrefaction temperatures (T ≥ 275 °C) has little or even adverse effect on the hydrophobicity of biochars. The longer holding time has a certain influence on the hydrophobicity of biochar, but the overall effect is not significant. The hydrophobicity of woody biochars (PWC and CWC) is better than that of straw biochars (WSC and CSC) at the same torrefaction conditions. The severe torrefaction of T ≥ 275 °C and τ ≥ 40 min are able to improve the hydrophobicity of woody biochars, however it has negative effect on straw biochars. The hydrophobicity of four biochars is ordered as PW > CW > WS ≈ CS at the same torrefaction conditions. The water adsorption mechanism of biochars is influenced by the coupling effects of physical structure evolution, release of hydrophilic oxygen-containing functional groups and pyrolytic tar condensation, and the severer the torrefaction, the more significant the influence is.

Biochar Adsorbents with Enhanced Hydrophobicity for Oil Spill Removal

Oil spills can cause massive loss of aquatic life and are costly to fishing and tourism industries. Current oil spill cleanup methods can be very expensive, have secondary environmental impacts, or be difficult to implement. This study employed five different adsorbents 1. Commercially available Douglas fir biochar (BC), S.A ~695 m2/g, pore volume ~ 0.26 cm3/g and pore diameter ~13-19.5 Å), 2. BC modified with lauric acid (LBC), 3. iron oxide-modified biochar (MBC), 4. LBC-modified with iron oxide (LMBC) and 5. MBC modified with lauric acid (MLBC) for oil recovery. Transmission, engine, machine and crude oils were used to simulate oil spills and perform adsorption experiments. All five adsorbents adsorbed all four oils with only a slight pH dependence, fast kinetics (sorptive equilibrium reached before 15 mins) and high regression fits to the pseudo-2nd-order kinetic model. The Sips isotherm model oil sorption capacities were in the range ~3-11 g oil/1 g adsorbent. Lauric acid-decorated biochar was found to have a higher oil adsorption capacity than the undecorated biochar. Lauric acid enhances biochar hydrophobicity and reduces water influx into biochar's porosity preventing it from sinking for 3 weeks. These features were observed even at 2% wt. of Lauric acid (doesn't sink for 2 weeks). Magnetization by magnetite nano particle deposition onto BC and LBC allows the recovery of the exhausted adsorbent by a magnetic field. Adsorption was robust under pseudo environmental conditions using simulated sea water. Oil sorption was endothermic. The oil-laden adsorbents' heating values were obtained, suggesting using these spent adsorbents as a low-cost fuel after recovery. Oil recovery and cyclic adsorption-desorption was also demonstrated using toluene as the stripping agent. The initial and oil-laden adsorbents were characterized by SEM, TEM, EDX, FT-IR, XRD, BET, TGA, DSC, VSM magnetometry, elemental analysis and XPS.

Linking hydrophobicity of biochar to the water repellency and water holding capacity of biochar-amended soil

Biochar addition to soil may change the hydrophobicity of amended soil and influence soil hydraulic properties. Soil hydrophobicity, i.e. soil water repellency (SWR) can interrupt water infiltration and form preferential flow leading to a potential risk of soil erosion or groundwater pollution. Up to date, the effect of different biochars on soil hydrophobicity remains unclear and the association of SWR with soil hydraulic properties is still unknown. To link the biochar hydrophobicity to SWR and soil water holding capacity (WHC), the surface structure and chemical composition of 27 biochars with different feedstocks and pyrolysis temperatures were characterized, and the SWR and soil WHC of biochar-added soil were investigated. Carboxylic groups on the biochar surface, surface area and pore volume were mostly influenced by pyrolysis temperature, which suggested the dominant factor determining the severity of biochar hydrophobicity was pyrolysis temperature. Hydrophilic soil became hydrophobic after biochar amendment. A higher addition rate led to a stronger SWR of hydrophilic soil. Biochar addition increased soil WHC of hydrophilic soil with low total organic carbon (TOC) content. Biochar did not have significant influence on SWR and soil WHC of hydrophobic soil with high TOC content. It implied that the influence of biochar on SWR and soil hydraulic properties mainly depended on soil original hydrophobicity and TOC content. Therefore, the properties of biochar and influence on soil hydrophobicity and hydraulic properties should be considered before processing biochar application.

Multifunctional Pd/Fe-biochar composites for the complete removal of trichlorobenzene and its degradation products

To elucidate the effect of structure and property of biochar on the structure-activity relationship among the composites of biochar supported Pd/Fe and 1,2,4-trichlorobenzene (1,2,4-TCB) and its dechlorination products, biochar supported Pd/Fe nanoparticles with different mass ratios were investigated for the enhanced removal of 1,2,4-TCB (52 μmol/L) and its dechlorination products. 1,2,4-TCB was removed through the electrochemical dechlorination by Pd/Fe and adsorption by biochar simultaneously. As the mass ratio of CS700 to Pd/Fe was 0.1:1, biochar within the Pd/Fe-CS7000.1 system played a significant role in the adsorption of 1,2,4-TCB. However, there is little adsorption to biochar for dechlorination products due to strong competition by 1,2,4-TCB. As the mass ratio of CS700 to Pd/Fe was increased to 5:1, 1,2,4-TCB was completely removed from the solution by the composites within 0.5 h. The dechlorination products (1,2-DCB, MCB, benzene and trace 1,3-DCB) were completely sequestered on solid phase but absent in aqueous solution. However, the excessive biochar increased the inaccessibility of 1,2,4-TCB or decreased the reactive sites of Pd/Fe leading to the less dechlorination of 1,2,4-TCB. The alkaline biochar did not influence the chemical reactivity of Pd/Fe in the composites and buffered the acid and alkaline solutions with pH being maintained at neutral conditions under initial pH ranging from 3.07 to 10.03. The highly hydrophobicity of biochar could maintain the affinity of the composite for the chlorinated compounds even if the concentration of 1,2,4-TCB was up to 80.9% of its aqueous solubility. This study provides efficient synergistic removal support for the treatment of TCB affected groundwater.

Possibilities to improve soil aggregate stability using biochars derived from various biomasses through slow pyrolysis, hydrothermal carbonization, or torrefaction

Various thermochemical conversion technologies can be applied in producing biochar from a wide range of raw materials. We studied the chemical quality of 10 different biochars produced via torrefaction (TOR), slow pyrolysis (SP), or hydrothermal carbonization (HTC), in order to assess their potential in improving clay soil aggregate stability and thus contribute to mitigation of erosion from agricultural soils. X-ray tomography was used to visualize soil aggregates in some selected biochar treatments.Feedstock type had a major influence on the properties of the biochar, but in general biochars derived through SP were alkaline and exhibited higher electrical conductivity and ash content and lower surface activity than acidic HTC and TOR biochars. Alkyl peak areas determined from FTIR spectra were higher in biochars produced by TOR and HTC than in SP biochars, which indicates a higher degree of hydrophobicity in the former. Significantly higher aggregate stability and reduced colloid detachment were achieved with HTC biochars, most likely due to hydrophobicity reducing wetting rate and aggregate slaking.When mixed with initially aggregated soil, the biochar particles settled in inter-aggregate voids. According to image analysis, the internal porosity of soil aggregates was not affected by biochar addition, i.e., biochar did not enter the aggregates during the short incubation period. Addition of hydrophobic HTC biochar decreased the soil water content at field capacity, whereas more inert SP chars tended to increase it. The overall effect of biochar hydrophobicity on soil functions needs to be explored prior to wider use of biochar as a soil amendment.

Sorptive removal of phenanthrene from aqueous solutions using magnetic and non-magnetic rice husk-derived biochars.

A magnetically modified rice husk biochar (MBC) was successfully prepared by a hydrothermal method from original biochar (BC) and subsequently used to remove phenanthrene (PHE) from aqueous solutions. The porosity, specific surface area and hydrophobicity of BC were significantly improved (approx. two times) after magnetic modification. The adsorption data fitted well to pseudo-second-order kinetic and Langmuir models. Compared with BC, MBC had a faster adsorption rate and higher adsorption capacity of PHE. The adsorption equilibrium for PHE on MBC was achieved within 1.0 h. The maximum adsorption capacity of PHE on MBC was 97.6 mg g−1 based on the analysis of the Sips model, which was significantly higher than that of other sources of BCs. The adsorption mechanism of the two BCs was mainly attributed to the action of surface functional groups and π–π-conjugated reactions. The adsorption of PHE on MBC mainly occurred in the functional groups of C–O and Fe3O4, but that on BC was mainly in the functional groups of –OH, N–H, C=C and C–O.

Properties and applications of biochars derived from different biomass feedstock sources

In China, substantial agricultural and garden wastes are burned yearly. This practice not only wastes resources but also pollutes air. Corn straw and poplar leaves are typical agricultural and garden waste in China. In this study, corn straw and poplar leaves were used to prepare biochars with different pyrolysis temperatures (250°C, 350°C, 450°C, 550°C and 650°C) and were labeled as CC (corn straw) and LC (poplar leaves), respectively. The biochars were characterized through elemental analysis, Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy and Fourier transform infrared spectroscopy. Yield, ash content and biochar pH were also measured. Results showed that the two biochars possessed some similar characteristics with increasing pyrolysis temperature. These attributes included increased carbon content, biochar hydrophobicity, alkaline pH; decreased hydrogen and oxygen contents and polar functional group content; and enlarged surface area. The biochars also displayed some different characteristics, such as the obviously larger surface area of CC than that of LC at high pyrolysis temperatures and the regular holes of CC and irregular and disordered holes of LC. When biochars CC-650 and LC-650 were used as soil conditioners, the soil pH increased by 0.3 and 0.4 units, respectively, and the soil cation exchange capacity increased by 12.7% and 21.5%, respectively, with respect to those of the blank controls. Keywords: biochars, corn straw, poplar leaves, pyrolysis, thermochemical property DOI: 10.3965/j.ijabe.20171002.2878 Citation: Bai X F, Zhou X Q, Li Z F, Ni J W, Bai X. Properties and applications of biochars derived from different biomass feedstock sources. Int J Agric & Biol Eng, 2017; 10(2): 242–250.

Are soil–water functions affected by biochar application?

Today biochar is considered a stable-carbon source that is able to improve soil quality. However, although biochar effects on some soil properties are already becoming well known, its impact on complex soil hydrological functions has yet to be better assessed. The main objectives are: (a) to determine the impact of different biochar amendments on important physical and chemical soil properties and (b) to determine whether the origin (biomass or sewage sludge) and pyrolysis technique can change biochar properties and regulate biochar influence on important soil functions, i.e. nutrient release, water sorption, and carbon storage. Six types of biochar produced from different biomass sources (pine, poplar or sludge) and pyrolysis processes (slow, fast or gasification) were applied to a sandy-loam, low-organic-matter, calcareous soil (mean dose: 18g/kg) and incubated in a greenhouse without seeding. Two sampling campaigns, one month and one year after biochar amendments, were performed. The overall impact of biochar, analysed by principal response curves (PRCs), indicated that it could improve or deteriorate soil hydrological properties at different intensities. Soil wettability was modified due to sludge biochar addition to soil by increased water penetration dynamics during the capillary rise process of about 18%. In contrast, water storage as a soil function during soil drying was not affected. Because no differences on aggregate stability were observed between treatments, increments on soil organic carbon could not be related to biochar physical protection caused by aggregate formation or by enhanced aggregate stability. As a result, carbon storage, considered as a soil function provided by biochar, was mainly related to its chemical stability. On the other hand, nutrient flux during soil slaking was improved, increasing nutrient release from soil to water. In terms of biochar properties, an increment of surface wettability of biochar during water drop penetration was observed after one year of its addition to soil, where the mean values of contact angle (CA) decreased 69.5%. This important result suggest that initial biochar hydrophobicity (CA>90°) disappeared after 1year. It was observed that PRC analysis was able to identify important key soil properties that should be monitored when biochar is used as soil amendment. We conclude that the impact of biochar on soil functions depends mainly on biochar feedstock rather than on the pyrolysis technique used during its production. In general, the performance of biochar obtained from sludge and vegetal biomass was markedly different.

The love–hate relationship of pyrolysis biochar and water: A perspective

Biochar is being considered for environmental sustainability by the scientific community and as a result is extensively investigated for various applications in agriculture, remediation and construction. Hence, a sound knowledge of biochar's physical and chemical properties is critical. However, the dynamics of biochar–water interaction remain ambiguous. We hypothesize that the hydrophobicity of a biochar made at low pyrolysis temperature is not permanent under water-rich conditions. Our results suggest that the aliphatic functional groups responsible for biochar's hydrophobicity are displaced when subjected to water which eventually increases the affinity of the biochar towards water. We envisage that commentary would stimulate researchers to investigate the biochar–water interaction in a new light and eventually help design a biochar which would be apt for their intended end use.