Influence of Al-oxide on pesticide sorption to woody biochars with different surface areas

Pesticide pollution: toxicity, sources and advanced remediation approaches

The Food and Agricultural Organization of the United Nations (FAO) estimates that food production must rise by 70% to meet the demands of an additional 2.3 billion people by 2050. This forecast underscores the persistent reliance on pesticides, making it essential to assess their toxicity and develop effective remediation strategies. Given the widespread utilisation of pesticides, it requires an urgent need to evaluate their toxicity and explore feasible remediation approaches for their removal. Hence, this review provides an overview of the latest information on the presence, distribution, sources, fate, and trends of pesticides in global environmental matrices, emphasizing the ecological and health risks posed by pesticide pollution. Currently, the dominant remediation techniques encompass physical, chemical, and biological methods, yet studies focusing on advanced remediation techniques remain limited. This review critically evaluates both newer and traditional approaches to pesticide removal, offering a descriptive and analytical comparison of various methods. The selection of the appropriate treatment method depends largely on the nature of the pesticide and the effectiveness of the chosen technique. In many cases, technologies such as membrane bioreactors and the fenton process could be integrated with biological technologies to enhance performance and overcome limitations. The study concludes that a hybrid approach combining various remediation strategies offers the most effective and sustainable solution for pesticide removal. Finally, the review underscores the need for further scientific investigation into the most viable technologies while discussing the challenges and prospects of developing safe, reliable, cost-effective, and eco-friendly methods for removing pesticides from the environment.

Desorption hysteresis of antibiotics on biochar produced at high temperature: The role of amine groups and amidation reaction

Knowledge of antibiotic desorption from high-temperature biochar is essential for assessing their environmental risks, and for the successful application of biochar to remove antibiotics. In previous studies, irreversible pore deformation, formation of charge-assisted hydrogen bonds or amide bonds were individually proposed to explain the desorption hysteresis of antibiotics on biochars, leading to a debate on hysteresis mechanism. In this study, desorption of sulfamethoxazole (SMX), ciprofloxacin (CFX) and tetracycline (TET) on a wood chip biochar produced at 700 °C (WBC700) and its oxidized product (O-WBC700) was investigated to explore the underlying hysteresis mechanism. Significant desorption hysteresis was observed for SMX, CFX and TET on WBC700 and O-WBC700. Hysteresis index (HI) of each antibiotic was higher on O-WBC700 with more oxygen-containing groups than WBC700, and was higher at lower equilibrium concentration. HI of antibiotics on WBC700 (or O-WBC700) increased in the order of SMX < CFX < TET. The calculated adsorption enthalpy of each antibiotic on WBC700 was positive, indicating an endothermic process. These phenomena together with FTIR, XPS spectra confirmed that the desorption hysteresis mechanism of antibiotics on high-temperature biochar is the formation of amide bonds by amidation reaction, but not the pore deformation or the hydrogen bond. Moreover, antibiotic can form amide bonds with WBC700 only if the amine group with pKa > 4.0, and the HI values were positively correlated with their pKa values. Amine group of antibiotics with higher pKa value show more nucleophilicity and could form stronger amide bonds with carboxyl group of biochar. The obtained results could help to solve the debate on desorption hysteresis mechanism of antibiotics on high-temperature biochars, and provide a new insight into the role of amine groups and amidation reaction on the hysteresis.

Efficient adsorption of short-chain perfluoroalkyl substances by pristine and Fe/Cu-loaded reed straw biochars

As the substitutes of legacy long-chain per-/polyfluoroalkyl substances (PFASs), short-chain PFASs have been widely detected in the environment. Compared to long-chain PFASs, short-chain PFASs have smaller molecules and are more hydrophilic. Therefore, they are more likely to experience long-distance transport and pose lasting environmental impacts. In this study, Fe-doped (R-Fe) and Cu-doped biochars (R-Cu) were prepared using reed straw biochar (R). The results showed that the PFBA and PFPeA sorption capacities of R-Fe were 25.81 and 43.59 mg g-1, 1.65 and 1.55 times higher than those of R, respectively. The PFBA and PFPeA sorption capacities of R-Cu were 19.34 and 33.69 mg g-1, 1.24 and 1.20 times higher than those of R, respectively. In addition, R, R-Fe, and R-Cu exhibited higher PFBA and PFPeA sorption capacities than the biochars previously reported. The excellent PFAS sorption performances of the biochars were attributed to the highly porous structure of R, which provided rich adsorption sites. Ion-pair sorption, pore filling, electrostatic interaction between the Fe/Cu and cationic groups on biochar and the anionic groups of PFASs, and hydrophobic interaction between the hydrophobic surface of biochar and the fluorinated tails of PFASs were the underlying sorption mechanisms. The biochars presented high removal rates (>86 %) of multiple PFASs (∑PFAS: 350 μg L-1) from synthetic wastewaters, including legacy and emerging PFASs of different chain lengths and with different functional groups. The biochars reported in this study are promising candidate adsorbents for treating waters contaminated with short-chain PFASs.

Metolachlor adsorption using walnut shell biochar modified by soil minerals

The removal of pesticide residues in soil is a research hotspot. The metolachlor (MET) adsorption by walnut shell biochar (BC) modified with montmorillonite (MBC), illite (IBC), and kaolinite (KBC), as well as the original BC (OBC) was investigated. The characteristics of samples were studied by scanning electron microscopy and mapping analysis, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry, and chemical stability analysis. The effects of the dosage, ionic strength, and pH, and determined the adsorption kinetics and isotherms for MET with the BCs were analyzed. In addition, response surface methodology regression model analysis was conducted and the adsorption mechanisms were investigated. The results showed that the thermal stability and chemical stability of MBC, IBC, and KBC were higher than those of OBC, and MBC had the greatest stability. The MET adsorption rates of OBC, MBC, IBC, and KBC were 62.15%, 92.47%, 87.97%, and 83.31%, respectively. The kinetic fitting results and adsorption mechanisms showed that the modification of BC with minerals enhanced the physical adsorption of MET. The maximum MET adsorption capacities by OBC, MBC, IBC, and KBC were 39.68 mg g^-1, 68.49 mg g^-1, 65.79 mg g^-1, and 65.36 mg g^-1, respectively. Hydrogen bonds, π-π bonds, coordination bonds, and hydrophobic interactions were the key adsorption mechanisms. Therefore, the mineral-modified BCs were characterized by high adsorption rates and stability. This approach can make BC more efficient, with higher performance as a low cost soil amendment.

Adsorption of metolachlor by a novel magnetic illite-biochar and recovery from soil

In this study, we investigated a highly efficient adsorbent that can be recycled from the soil. Walnut shells were used as raw materials to prepare original ecological biochar (OBC), illite modified biochar (IBC), FeCl₃ modified biochar (magnetic biochar; MBC), and illite and FeCl₃ modified biochar (IMBC), which were tested as low-cost adsorbents. The agents were used to remove metolachlor (MET) from soil. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, magnetic sensitivity curve analysis, and a series of adsorption experiments were conducted to study the interaction between illite and MBC, and the effect on MET adsorption. Compared with OBC, IMBC had more adsorption sites on the surface. IMBC improved the hole filling effect during the adsorption process. IMBC had more oxygen-containing functional groups and it performed better at removing organic matter through π-π interactions. According to the Langmuir model, the Q₀ values for IBC, MBC, and IMBC were 91.74 mg g^-1, 107.53 mg g^-1, and 129.87 mg g^-1, respectively, which were significantly higher than that for OBC (72.99 mg g^-1). The response surface model was used to explore the optimal adsorption conditions for IMBC. After three regeneration cycles, the MET adsorption rate with IMBC was still 81.38% and the MET recovery rate was 98.12%. Therefore, IMBC was characterized as an adsorbent with high efficiency, low cost, and good recyclability. In addition, we propose a suitable agricultural system for recovering MBC on site in the field.