Sorption of N-acyl homoserine lactones on maize straw derived biochars: Characterization, kinetics and isotherm analysis

Enhancing Methane Production in Anaerobic Digestion of Food Waste Using Co-Pyrolysis Biochar Derived from Digestate and Rice Straw

Anaerobic digestion (AD) is a preferred method for food waste (FW) treatment due to its sustainability and potential for production of renewable bioenergy. However, the accumulation of volatile fatty acids (VFAs) and ammonia often destabilizes the AD process, and managing the digestate byproduct poses additional challenges. This study investigates the use of co-pyrolysis biochar synthesized from digestate and rice straw (DRB) to enhance methane production and AD efficiency. DRB addition increased cumulative methane yield by 37.1%, improved VFA conversion efficiency, and achieved a 42.3% higher NH3-N-removal rate compared to the control group. The COD-removal rate was 68.7% throughout the process. Microbial analysis revealed that DRB selectively enriched Fastidiosipila and Methanosarcina, promoting direct interspecies electron transfer (DIET) and methane yield. These findings highlight DRB's potential to enhance AD efficiency and support closed-loop resource utilization.

Roles of quorum-sensing molecules in methane production from anaerobic digestion aided by biochar

Biochar has been used to enhance methane generation from anaerobic digestion through establishing direct interspecific electron transfer between microorganisms. However, the microbial communication is still inadequate, thereby limiting further methane production improvement contributed by biochar. This study investigated the roles of quorum-sensing molecules, acylated homoserine lactone (AHL), in anaerobic digestion of waste activated sludge aided by biochar. Results showed that the co-addition of separated biochar and AHL achieved best methane production performance, with the maximal methane yield of 154.7 mL/g volatile suspended solids, which increased by 51.9%, 47.2%, 17.9%, and 39.4% respectively compared to that of control, AHL-loaded biochar, sole AHL, and sole biochar groups. The reason was that the co-addition of separated biochar and AHL promoted the stages of hydrolysis and acidification, promoting the conversion of organic matters and short-chain fatty acids, and optimizing the accumulation of acetate acid. Moreover, the methanogenesis stage also performed best among experimental groups. Correspondingly, the highest activities of electron transfer and coenzyme F420 were obtained, with increase ratios of 33.2% and 27.2% respectively compared to that of control. Furthermore, biochar did more significant effects on the evolution of microbial communities than AHL, and the direct interspecific electron transfer between fermentative bacteria and methanogens were possibly promoted.

Nanomaterials and biochar mediated remediation of emerging contaminants

The unrestricted release of various toxic substances into the environment is a critical global issue, gaining increased attention in modern society. Many of these substances are pristine to various environmental compartments known as contaminants/emerging contaminants (ECs). Nanoparticles and emerging sorbents enhanced remediation is a compelling methodology exhibiting great potential in addressing EC-related issues and facilitating their elimination from the environment, particularly those compounds that demonstrate eco-toxicity and pose considerable challenges in terms of removal. It provides a novel technique enabling the secure and sustainable removal of various ECs, including persistent organic compounds, microplastics, phthalate, etc. This extensive review presents a critical perspective on the current advancements and potential outcomes of nano-enhanced remediation techniques such as photocatalysis, nano-sensing, nano-enhanced sorbents, bio/phyto-remediation, which are applied to clean-up the natural environment. In addition, when dealing with residual contaminants, special attention is paid to both health and environmental implications; therefore, an evaluation of the long-term sustainability of nano-enhanced remediation methods has been considered. The integrated mechanical approaches were thoroughly discussed and presented in graphical forms. Thus, the critical evaluation of the integrated use of most emerging remediation technologies will open a new dimension in environmental safety and clean-up program.

Study of the biofilm mechanism of C4-HSL and C6-HSL in the degradation of quinoline

Quinoline is a hard-to-degrade organic compound widely found in coal chemical wastewater, that seriously affects the ecological environment and human health. A number of biochemical methods are already available for quinoline degradation, but the use of microbial community sensing for quinoline degradation has not been studied in depth. Therefore, this paper focuses on the enhanced mechanism of quorum-sensing signaling molecules in the biofilm formation process during quinoline degradation by functional strains of bacteria. In this paper, the effects of the signal molecules C4-HSL and C6-HSL on the adhesion ability, colony diameter, biofilm formation ability and biofilm morphology of functional strains of quinoline degrading bacteria (Ochrobactrum sp., LC-1) were investigated, and the results showed that both signal molecules promoted the biofilm formation process during the degradation of quinoline by exhibiting an efficient biofortification effect. Both signal molecules could enhance the colony diameter of strain LC-1, where C4-HSL could enhance the biomass of strain LC-1 and stimulate the secretion of extracellular polysaccharides; and C6-HSL could induce the enhancement of adhesion performance and the secretion of extracellular proteins from strain LC-1; both molecules together enhanced the biofilm formation process of strain LC-1. This study has practical application in the degradation of quinoline in coal chemical wastewater.

Effects of ball milling on biochar adsorption of contaminants in water: A meta-analysis

Reckless release of contaminants into the environment causes pollution in various aquatic systems on a global scale. Biochar is potentially an inexpensive and environmentally friendly adsorbent for removing contaminants from water. Ball milling has been used to enhance biochar's functionality; however, global analysis of the effect of ball milling on biochar's capacity to adsorb contaminants in aqueous solutions has not yet been done. Here, we conducted a meta-analysis to investigate the effects of ball milling on the adsorption/removal capacity of biochar for contaminants in aqueous solutions, and to investigate whether ball milling effects are related to biochar production, ball milling, and other experimental variables. Overall, ball milling significantly increased biochar adsorption capacity towards both inorganic and organic contaminants, by 69.9% and 561.9%, respectively. This could be attributed to ball milling increasing biochar surface area by 2.05-fold, pore volume by 2.39-fold, and decreasing biochar pH by 0.83-fold. The positive adsorption effects induced by ball milling varied widely, with the most effective being ball milling for 12 to 24 h at 300 to 400 rpm with a biochar:ball mass ratio of 1:100 on biochars produced at 400-550 °C from wood residues. Based on this meta-analysis, we conclude that ball milling could effectively enhance biochar's ability to remove organic and inorganic contaminants from aquatic systems.

Preparation of Biochar with Developed Mesoporous Structure from Poplar Leaf Activated by KHCO3 and Its Efficient Adsorption of Oxytetracycline Hydrochloride

The effective removal of oxytetracycline hydrochloride (OTC) from the water environment is of great importance. Adsorption as a simple, stable, and cost-effective technology is regarded as an important method for removing OTC. Herein, a low-cost biochar with a developed mesoporous structure was synthesized via pyrolysis of poplar leaf with potassium bicarbonate (KHCO₃) as the activator. KHCO₃ can endow biochar with abundant mesopores, but excessive KHCO₃ cannot continuously promote the formation of mesoporous structures. In comparison with all of the prepared biochars, PKC-4 (biochar with a poplar leaf to KHCO₃ mass ratio of 5:4) shows the highest adsorption performance for OTC as it has the largest surface area and richest mesoporous structure. The pseudo-second-order kinetic model and the Freundlich equilibrium model are more consistent with the experimental data, which implies that the adsorption process is multi-mechanism and multi-layered. In addition, the maximum adsorption capacities of biochar are slightly affected by pH changes, different metal ions, and different water matrices. Moreover, the biochar can be regenerated by pyrolysis, and its adsorption capacity only decreases by approximately 6% after four cycles. The adsorption of biochar for OTC is mainly controlled by pore filling, though electrostatic interactions, hydrogen bonding, and π-π interaction are also involved. This study realizes biomass waste recycling and highlights the potential of poplar leaf-based biochar for the adsorption of antibiotics.

Predicting the speciation of ionizable antibiotic ciprofloxacin by biochars with varying carbonization degrees†

Sorption mechanisms of ionizable organic pollutants by biochars and approaches for the prediction of sorption are still unclear. In this study, batch experiments were conducted to explore the sorption mechanisms of woodchip-derived biochars prepared at 200–700 °C (referred as WC200–WC700) for cationic, zwitterionic and anionic species of ciprofloxacin (referred as CIP⁺, CIP^± and CIP⁻, respectively). The results revealed that the sorption affinity of WC200 for different CIP species was in the order of CIP^± > CIP⁺ > CIP⁻, while that of WC300–WC700 remained the order of CIP⁺ > CIP^± > CIP⁻. WC200 exhibited a strong sorption ability, which could be attributed to hydrogen bonding and electrostatic attraction with CIP⁺, electrostatic attraction with CIP^±, and charge-assisted hydrogen bonding with CIP⁻. Pore filling and π–π interactions contributed to the sorption of WC300–WC700 for CIP⁺, CIP^± and CIP⁻. Rising temperature facilitated CIP sorption to WC400 as verified by site energy distribution analysis. Proposed models including the proportion of the three CIP species and sorbent aromaticity index (H/C) can quantitatively predict CIP sorption to biochars with varying carbonization degrees. These findings are vital to elucidating the sorption behaviors of ionizable antibiotics to biochars and exploring potential sorbents for environmental remediation.

This study revealed the evolution of sorption mechanisms with pyrolysis temperature of biochar and CIP speciation, and provided a novel approach for the sorption prediction of ionizable antibiotics.

Effects of biochar on anaerobic treatment systems: Some perspectives

Many anaerobic activities involve carbon, nitrogen, iron, and sulfur cycles. As a well-developed porous material with abundant functional groups, pyrolytic biochar has been widely researched in efforts to promote microbial activities. However, the lack of consensus on the biochar mechanism has limited its practical application. This review summarizes the effects of different pyrolysis temperatures, particle sizes, and dosages of biochar on microbial activities and community in Fe(III) reduction, anaerobic digestion, nitrogen removal, and sulfate reduction systems. It was found that biochar could promote anaerobic activities by stimulating electron transfer, alleviating toxicity, and providing suitable habitats for microbes. However, it inhibits microbial activities by releasing heavy metal ions or persistent free radicals and adsorbing signaling molecules. Finding a balance between the promotion and inhibition of biochar is therefore essential. This review provides valuable perspectives on how to achieve efficient and stable use of biochar in anaerobic systems.

Mechanisms of biochar enhanced Cu2O photocatalysts in the visible-light photodegradation of sulfamethoxazole

Cu₂O nanoparticles are decorated with biochars derived from spent coffee grounds (denoted as Cu₂O/SCG) and applied as visible-light-active photocatalysts in the sulfamethoxazole (SMX) degradation. The physicochemical properties of Cu₂O/SCG are identified by various spectral analysis, electrochemical and photochemical techniques. As a result, the Cu₂O/SCG exhibits the higher removal efficiency of SMX than the pristine Cu₂O under visible light irradiation. We can observe that Cu₂O could be incorporated onto the SCG biochars with rich oxygen vacancies/adsorbed hydroxyl groups. In addition, the Cu₂O/SCG has the lower charge transfer resistance, faster interfacial electron transfer kinetics, decreased recombination of charge carriers and superior absorbance of visible light. The construction of band diagrams for Cu₂O/SCG and pristine Cu₂O via UV-vis spectra and Mott-Schottky plots suggest that the band energy shifts and higher carrier density of Cu₂O/SCG may be responsible for the photocatalytic activity enhancements. From the radical scavenger experiments and electron paramagnetic resonance spectra, the aforementioned energy shifts could decrease the energy requirement of transferring photoinduced electrons to the potential for the formation of active superoxide radicals (·O₂^-) via one and two-electron reduction routes in the photocatalytic reaction. A proposed degradation pathway shows that ·O₂^- and h⁺ are two main active species which can efficiently degrade SMX into reaction intermediates by oxidation, hydroxylation, and ring opening. This research demonstrates the alternative replacement of conventional carbon materials for the preparation of biochar-assisted Cu₂O photocatalysts which are applied in the environmental decontamination by using solar energy.

Biochar-microorganism interactions for organic pollutant remediation: Challenges and perspectives

Numerous harmful chemicals are introduced every year in the environment through anthropogenic and geological activities raising global concerns of their ecotoxicological effects and decontamination strategies. Biochar technology has been recognized as an important pillar for recycling of biomass, contributing to the carbon capture and bioenergy industries, and remediation of contaminated soil, sediments and water. This paper aims to critically review the application potential of biochar with a special focus on the synergistic and antagonistic effects on contaminant-degrading microorganisms in single and mixed-contaminated systems. Owing to the high specific surface area, porous structure, and compatible surface chemistry, biochar can support the proliferation and activity of contaminant-degrading microorganisms. A combination of biochar and microorganisms to remove a variety of contaminants has gained popularity in recent years alongside traditional chemical and physical remediation technologies. The microbial compatibility of biochar can be improved by optimizing the surface parameters so that toxic pollutant release is minimized, biofilm formation is encouraged, and microbial populations are enhanced. Biocompatible biochar thus shows potential in the bioremediation of organic contaminants by harboring microbial populations, releasing contaminant-degrading enzymes, and protecting beneficial microorganisms from immediate toxicity of surrounding contaminants. This review recommends that biochar-microorganism co-deployment holds a great potential for the removal of contaminants thereby reducing the risk of organic contaminants to human and environmental health.