A feasible biochar derived from biogas residue and its application in the efficient adsorption of tetracycline from an aqueous solution

Synthesis of surficial-modified green biochar catalyst generated by biogas residue biochar and potential application for catalytic ozonation degradation of ciprofloxacin

This study synthesized novel, green, and easily recoverable surface-modified economical catalysts via hydrothermal treatment (HT) successfully, utilizing biogas residue biochar (BRB), a food waste product from anaerobic fermentation, pyrolyzed at 500 °C for 50 min. Using autoclaves, a total of six solutions were prepared, each having 1 g fine-grinded BRB, surficial modified by adding glycerol (GL) (10 or 20 mL) and SDI water (70 or 60 mL), and heated in an oven at 240 °C, 180 °C, and 120 °C for 24 h. Afterward, the catalysts showed the potential for degradation of widely used emerging pollutants like ciprofloxacin. Taking advantage of catalytic surface modification, the catalytic ozonation degradation was more effective than that of a single ozonation. However, under similar conditions, catalyst amount 0.20 g, ozone dose 15 mg L-1, and ciprofloxacin 80 mg L-1, the performance of the 10 mL GL-180 °C catalyst was excellent. It showed a 92.45%-94.41% optimum removal rate in the 8-10 min interval. After five continuous cycles, the 10 mL GL-180 °C catalyst exhibited excellent stability and reusability. XPS, FT-IR, BET, XRD, and SEM before and after the reaction confirmed the successful synthesis and degradation mechanism. A possible degradation pathway was unrevealed based on a liquid chromatography-mass spectrometer (LC-MS) and scavenger test, proving the significant roles of superoxide radicals (O2•-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Further, Electron paramagnetic resonance (EPR) analysis confirmed the presence of active oxygen species. Subsequently, 10 mL GL-180 °C showed promising degradation for the actual water environment, such as groundwater (73.55%) and river water (64.74%). This work provides a valuable economic strategy to convert biogas residue biochar into a low-cost catalyst for organic pollutant decomposition.

Unlocking the potential of Chinese herbal medicine residue-derived biochar as an efficient adsorbent for high-performance tetracycline removal

This study employed hydrothermal carbonization (HTC) in conjunction with ZnCl2 activation and pyrolysis to produce biochar from one traditional Chinese medicine astragali radix (AR) residue. The resultant biochar was evaluated as a sustainable adsorbent for tetracycline (TC) elimination from water. The adsorption performance of TC on two micropore-rich AR biochars, AR@ZnCl2 (1370 m2 g-1) and HAR@ZnCl2 (1896 m2 g-1), was comprehensively evaluated using adsorption isotherms, kinetics, and thermodynamics. By virtue of pore diffusion, π-π interaction, electrostatic attraction, and hydrogen bonding, the prepared AR biochar showed exceptional adsorption properties for TC. Notably, the maximum adsorption capacity (930.3 mg g-1) of TC on HAR@ZnCl2 can be achieved when the adsorbent dosage is 0.5 g L-1 and C0 is 500 mg L-1 at 323 K. The TC adsorption on HAR@ZnCl2 took place spontaneously. Furthermore, the impact of competitive ions behavior is insignificant when coexisting ion concentrations fall within the 10-100 mg L-1 range. Additionally, the produced biochar illustrated good economic benefits, with a payback of 701 $ t-1. More importantly, even after ten cycles, HAR@ZnCl2 still presented great TC removal efficiency (above 77%), suggesting a good application prosperity. In summary, the effectiveness and sustainability of AR biochar, a biowaste-derived product, were demonstrated in its ability to remove antibiotics from water, showing great potential in wastewater treatment application.

Effect of citric acid modification on the properties of hydrochar and pyrochar and their adsorption performance toward methylene blue: crucial roles of minerals and oxygen functional groups

Modification is widely used to enhance the adsorption performance of pristine hydrochar (HBC) and pyrochar (BC). However, comparisons between modified HBC and BC toward pollutant removal have rarely been reported. In this study, pristine HBC and BC derived from rice straw were first produced, and then citric acid (CA) was used as a modifier to synthesize CA-modified HBC (CAHBC) and CA-modified BC (CABC). Furthermore, the adsorption performance of biochars toward methylene blue (MB) was investigated. The results showed that BC exhibits relatively rough surfaces and contains more minerals (ash), whereas HBC has plentiful O-containing functional groups and fewer minerals. CA modification partially removed minerals from the surface of BC, which weakened the ion exchange, surface complexation, and n-π interaction, resulting in a lower adsorption ability toward MB. By contrast, CA produced more O-containing functional groups on the surface of HBC, which strengthened the hydrogen bonding and electrostatic interaction, thus increasing the adsorption capacity toward MB. The two-compartment model showed a good fit to the adsorption process of MB on CAHBC, and the isotherm data for MB adsorption by HBC and CAHBC are suitable for the Freundlich model. The highest adsorption amount of MB using CAHBC was 80.13 mg·g-1, which was 27.66% higher than that for CABC. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the carboxyl groups in the surface functional groups of CAHBC played a crucial role in the MB adsorption process. In addition, CAHBC showed a good performance for a wide range of pH values (4.0-10.0) and under the interference of coexisting ions, and also presented a recycling ability. Furthermore, the adsorption of MB on CAHBC biochar was a spontaneous, exothermic, degree-of-randomness-increasing process. Consequently, CA modification of HBC is a promising strategy and could be used for MB removal from aquatic environments.

Co-composting of green waste and biogas waste: physical, chemical parameters and quality of ripe compound

The impact of adding biogas waste (BW) to green waste (GW) composting to increase nitrogen supplementation and improve mature compost quality was investigated. Conducted over 90 days using static windrows, the experiment compared treatments with GW alone (T1) and GW supplemented with BW (T2 and T3). The results showed that the addition of BW increased temperatures, improved the C/N ratio, and expedited the stabilization process compared to T1. Furthermore, the addition of BW led to significant degradation of hemicellulose (up to 39.98%) and cellulose (up to 27.63%) compared to GW alone. Analysis of Fourier-transform infrared (FTIR) spectra revealed the presence of aromatic, phenolic, aliphatic, and polysaccharide structures in the compost, with BW supplementation enhancing these characteristics. Importantly, the germination index (GI) assessment indicated that the compounds produced were not toxic and instead exhibited stimulatory effects on seed germination. Overall, the findings suggest that supplementing GW composting with BW can enhance the quality and efficacy of the composting process, resulting in compost with desirable properties for agricultural use.

Adsorption Characteristics of Ball Milling-Modified Chinese Medicine Residue Biochar Toward Quercetin

Using traditional Chinese medicine residues as raw materials, different biochars (BC) were prepared through oxygen-limited pyrolysis at 300 °C, 500 °C, and 700 °C, and BC was ball-milled to produce ball-milled biochar (BMC). Using these adsorbents to adsorb the allelopathic autotoxic substance quercetin. The physical and chemical properties of various biochars derived from traditional Chinese medicine residues were characterized using the Brunauer-Emmett-Teller-N2 surface areas (BET), scanning electron microscopy (SEM), Fourier transform IR spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy (Raman). The study investigated the effects of the initial pH value, different humic acid concentrations, and multiple adsorption-desorption experiments on the removal of quercetin from the solution. The article discusses the adsorption mechanism of quercetin in solution by biochar from a traditional Chinese medicine residue, based on the results of adsorption kinetics and adsorption isotherm fitting. The findings indicate that increasing the pyrolysis temperature reduces the oxygen-containing functional groups of BC, enhances the aromaticity, and stabilizes the carbon structure. The pore structure of BMC becomes more complex after ball milling, which increases the number of oxygen-containing functional groups on the surface. Among the samples tested, BMC700 exhibits the best adsorption performance, with an adsorption capacity of 293.3 mg·g-1 at 318 K. The adsorption process of quercetin by BMC700 follows the pseudo-second-order kinetic model and the Freundlich adsorption isotherm model. The process is primarily a form of multimolecular layer adsorption. Its mechanism involves the pore-filling effect, hydrogen-bonding interaction, electrostatic interaction, and π-π coexistence, as well as the yoke effect. Additionally, they are highly recyclable and show promise in addressing continuous cropping issues.

A comprehensive review on the preparation of biochar from digestate sources and its application in environmental pollution remediation

The preparation of biochar from digestate is one of the effective ways to achieve the safe disposal and resource utilization of digestate. Nevertheless, up to now, a comprehensive review encompassing the factors influencing anaerobic digestate-derived biochar production and its applications is scarce in the literature. Therefore, to fill this gap, the present work first outlined the research hotspots of digestate in the last decade using bibliometric statistical analysis with the help of VOSviewer. Then, the characteristics of the different sources of digestate were summarized. Furthermore, the influencing factors of biochar preparation from digestate and the modification methods of digestate-derived biochar and associated mechanisms were analyzed. Notably, a comprehensive synthesis of anaerobic digestate-derived biochar applications is provided, encompassing enhanced anaerobic digestion, heavy metal remediation, aerobic composting, antibiotic/antibiotic resistance gene removal, and phosphorus recovery from digestate liquor. The economic and environmental impacts of digestate-derived biochar were also analyzed. Finally, the development prospect and challenges of using biochar from digestate to combat environmental pollution are foreseen. The aim is to not only address digestate management challenges at the source but also offer a novel path for the resourceful utilization of digestate.

Integrating g-C3N4 nanosheets with MOF-derived porous CoFe2O4 to form an S-scheme heterojunction for efficient pollutant degradation via the synergy of photocatalysis and peroxymonosulfate activation

When confronted with wastewater that is characterized by complex composition, stable molecular structure, and high concentration, relying solely on photocatalytic technology proves inadequate in achieving satisfactory degradation results. Therefore, the integration of other highly efficient degradation techniques has emerged as a viable approach to address this challenge. Herein, a novel strategy was employed whereby the exfoliated g-C3N4 nanosheets (CNs) with exceptional photocatalytic performance, were intimately combined with porous rod-shaped cobalt ferrite (CFO) through a co-calcination process to form the composite CFO/CNs, which exhibited remarkable efficacy in the degradation of various organic pollutants through the combination of photocatalysis and Fenton-like process synergistically, exemplified by the representative case of tetracycline hydrochloride (TCH, 200 mL, 50 mg/L). Specifically, under 1 mM of peroxymonosulfate (PMS) and illumination conditions, 50 mg of 1CFO/9CNs achieved a TCH removal ratio of ∼90% after 60 min of treatment. Furthermore, this work comprehensively investigated the influence of various factors, including catalyst and PMS dosages, solution pH, and the presence of anions and humate, on the degradation efficiency of pollutants. Besides, quenching experiments and EPR tests confirmed the establishment of an S-scheme heterojunction between CNs and CFO, which facilitated the effective spatial separation of photoexcited charge carriers and preserved the potent redox potential of photogenerated electrons and holes. This work offers a valuable reference for the integration of photocatalysis with the PMS-based Fenton-like process.

Thiamethoxam adsorption by ZnCl2 modified cow manure biochar: Mechanism and quantitative prediction

The overuse of thiamethoxam (THM) has threatened the survival of living organisms and it is necessary to find an environmentally friendly material to remove THM frequently detected in water. Biochar prepared from cow manure modified with ZnCl2 (Zn-CBC) was used to remove THM. Compared to the unmodified cow manure biochar (CBC), the removal ratio of THM by Zn-CBC was enhanced 35 times. In the mechanistic analysis, SEM and BET showed that Zn-CBC had a good pore structure and its specific surface area (166.502 m2 g-1) increased to 17 times that of CBC, indicating that Zn-CBC had good pore adsorption properties. The adsorption kinetic and isotherm implied that the main mechanism was chemisorption including π-π interaction and H-bonding. Furthermore, the stable graphitized structure of Zn-CBC allowed for efficient adsorption and reusability. In addition, this study constructed an intelligent prediction model using batch experiment data, and the high R2 (0.978) and low RMSE (0.057) implied that the model could accurately and quantitatively predict the adsorption efficiency. This paper provides a novel perspective to simultaneously remove the neonicotinoid insecticides and realize the resource utilization of cow manure.

Efficiently catalytic degradation of tetracycline via persulfate activation with plant-based biochars: Insight into endogenous mineral self-template effect and pyrolysis catalysis

Endogenous mineral of plant such as potassium, calcium and iron may play a crucial role in boosting the physicochemical structure and catalytic activity of high temperature pyrolyzed plant-based biochar while it is often neglected owing to its relative less content. Herein, self-template pyrolyzed plant-based biochars were prepared from two different ash-contained agricultural wastes of peanut hull (PH, 3.2% ash) and cotton straw (CS, 0.8% ash), and aimed at investigating the relationship among the endogenous mineral fractions of plant-based biomass, physicochemical active structure and persulfate (PS) catalytic degradation activity for tetracycline (TC). The results of energy/spectral characterization showed that under the self-template effect and pyrolysis catalysis of endogenous minerals, PH biochar (PBC) possessed much more specific surface area, conjugated graphite domain, C=O and pyrrolic-N surface active functional sites than CS biochar (CBC), enhancing TC removal rate of PBC/PS to 88.37%, twice that of CBC/PS (44.16%). Meanwhile, reactive oxygen quenching and electrochemical experiments showed that electrons transfer and non-free radical pathways based on singlet oxygen contributed 92% of TC removal in PBC/PS system. Remarkably, by comparing the differences in structure and TC removal performance of pre-deashing and non-deashing prepared plant-based biochars, a possible mechanism for endogenous mineral components' self-template effect and pyrolysis catalysis role of plant-based biomass was proposed. This study provides a new insight for revealing the intrinsic mechanism of mineral elements enhancing the active surface structures and catalytic properties of plant-based biochars derived from distinct feedstocks.

Selective adsorption of tetracycline and copper(II) on ion-imprinted porous alginate microspheres: performance and potential mechanisms

A novel epichlorohydrin and thiourea grafted porous alginate adsorbent (UA-Ca/IIP) was synthesized using ion-imprinting and direct templating to remove copper ions (Cu(II)) and tetracycline (TC) in aqueous solution. UA-Ca/IIP demonstrated great selectivity for Cu(II) and TC among different coexisting anions (CO32-, PO43- and SO42-), cations (Ca2+, Mg2+ and NH4+), and antibiotics (oxytetracycline and sulfamethoxazole). The adsorption of TC and Cu(II) by UA-Ca/IIP was significantly affected by the pH of the solution, and the quantity of TC and Cu(II) adsorbed reached a maximum at pH 5. A pseudo-second-order model better fitted the kinetic data; the Langmuir model predicted the maximum adsorption quantities 3.527 mmol TC g-1 and 4.478 mmol Cu(II) g-1 at 298 K. Thermodynamic studies indicated that the TC and Cu(II) adsorption was more rapid at a higher temperature. Antagonistic and synergistic adsorption experiments showed that the adsorption capacity of TC would increase significantly with the increase of Cu(II) concentration. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that along with the influence of pH, electrostatic interaction and complexation were the main mechanisms of TC and Cu(II) adsorption. Regeneration experiments revealed that TC and Cu(II) were removed efficiently and that UA-Ca/IIP was recyclable over the long term. These results show that the modified porous alginate microsphere is a green and recyclable adsorbent, which has good selectivity and high adsorption performance for the removal of TC and Cu(II).

"Blockchain-Like" MIL-101(Cr)/Carbon Black Electrodes for Unprecedented Defluorination by Capacitive Deionization

Metal-organic frameworks (MOF) have attracted extensive attention due to their ultra-high specific surface area and tunable structure, the mechanism of direct utilization for capacitive deionization (CDI) defluorination remains undefined. Here, MIL-101(Cr) with ultra-high specific surface area, high water stability, and open metal sites (OMSs) is prepared by a hydrothermal method for defluorination of CDI. Carbon black is used as a "chain" to connect F-stored in the holes of MIL-101(Cr) (Cr-MOF)as "blocks" to enhance the conductivity and ion storage capacity of MIL-101(Cr)/carbon black electrodes (Cr-MOF electrodes). This simple construction method avoids the process complexity of in situ synthesis and performs better. These easily constructed "blockchain-like" Cr-MOF electrodes exhibit excellent defluorination capacity (39.84 mg_NaF g_electrodes ^-1 ), low energy consumption (1.2 kWh kg_NaF ^-1 ), and good stability. The coupling of the electrochemical redox reaction of Cr³⁺ /Cr⁴⁺ with confined water is investigated using in situ and ex situ analysis methods combined with density functional theory (DFT), resulting in an unprecedented defluorination mechanism for Cr-MOF electrodes. This study opens up new ideas for the application of MOF in CDI, clarifies the removal mechanism of MOF, and lays a foundation for further promoting the application of raw materials with poor conductivity in the field of CDI.

Peroxymonosulfate activation by nitrogen-doped herb residue biochar for the degradation of tetracycline

Biochar is an environmentally friendly material with potential applications in water purification. In this study, herb residue nitrogen-doped biochar (N-BC) was fabricated and used to activate peroxymonosulfate (PMS). Characterization and density-functional theory (DFT) studies were conducted to explore the influence of nitrogen doping. Radical scavenging activity and electron paramagnetic resonance (EPR) spectroscopy revealed that non-radical singlet oxygen (¹O₂) is the main reactive oxidative species. Additionally, pyridinic-N was shown to play a pivotal role in the ¹O₂-dominated pathway. Three possible degradation pathways were proposed based on the identified degradation intermediates. Batch experiments confirmed that N-BC showed excellent catalytic performance and reusability. The best condition for tetracycline (TC) degradation efficiency (>99%) in 60 min was obtained when the dosage of N-BC was 1 g/L and the concentration of PMS was 5 mM. Furthermore, N-BC showed approximately 65.5% degradation efficiency within 4 cycles. Furthermore, the toxicity of degradation intermediates was examined using ECOSAR and T.E.S.T procedures. This study brings forth a feasible strategy to synthesize biochar. Furthermore, the proposed approach will facilitate the use of biochar in water purification.

Effect of water-washing pretreatment on the enhancement of tetracycline adsorption by biogas residue biochar

Biochar preparation was a feasible strategy for realizing the reduction, harmlessness, and resource utilization of biogas residue (BR) simultaneously. How to enhance the adsorption performance of biogas residue biochar through simple, friendly, and effective way still needs to be investigated. In this study, water-washing pretreatment of BR was adopted before biochar preparation (BRBC-W), and pristine biochar (BRBC) was also produced to serve as control. The adsorption behavior and possible adsorption mechanisms of tetracycline (TC) onto biochars were comprehensively studied. The results showed that water-washing pretreatment could increase the surface area and mesoporous volume of biochar from 358.63 to 391.98 cm³∙g^-1, and 0.459 to 0.488 cm³∙g^-1, respectively. More graphitic structure was observed in BRBC-W. In addition, the surface morphology, element content, minerals composition, and surface functional groups also changed in biochar after water-washing pretreatment. The pseudo-second-order and Redlich-Peterson models better descried the adsorption behavior of TC on BCRBC-W. The maximum adsorption capacity of BRBC and BRBC-W for TC based on Langmuir isotherm was 224.93 and 306.94 mg·g^-1, respectively. The adsorption affinity of BRBC-W toward TC was greater than that of BRBC. BRBC and BRBC-W can effectively remove TC in water within a wide pH range and under the interference of co-existing ions. The adsorption mechanism of TC onto BRBC and BRBC-W included ore filling, π-π interaction, and hydrogen bonding. The enhancement of TC on BRBC-W by water-washing pretreatment was attributable to the strengthening of pore diffusion and π-π interaction. Therefore, water-washing pretreatment effectively enhanced the adsorption performance of BRB, and BRBC-W was an effective eco-friendly adsorbent for the removal of TC from aquatic environment.

Insights into leachate reduction in landfill with different ventilation Rates: Balance of Water, waste physicochemical Properties, and microbial community

Ventilation is an efficient approach employed for accelerating stabilization and reducing aftercare of landfill, but its effect on leachate reduction is still elusive. To fill this knowledge gap, five lab-scale landfill reactors with different ventilation rates were established in this study. Suitable ventilation (e.g. 0.25-0.5 L·min^-1·kg^-1 dry solid of waste (DS)) was beneficial to promoting the stabilization of landfill, which effectively accelerated the degradation of organic matter and reduced water content of landfilled waste. Based on the mass balance of water, the dominant input water was initial water of landfilled waste (more than 94 %), which was partially converted to leachate and evaporated water. Ventilation enhanced the intensity of biochemical reactions heat to increase evaporated water content from 0 to 0.29 t/t DS while reducing the leachate generation significantly from 0.69 to 0.49 t/t DS with the increase of ventilation rate. Besides, the hydrophilic substances, such as humic acid-like substances, in landfilled waste increased, and the surface of the landfilled waste converted from smooth to rough. The reduction of the bound water content has a significant correlation with the degradation of organic matter content (p less than 0.05), which reduced the water-holding capacity of waste. Actinobacteriota and Firmicutes were the key bacterial phyla in the degradation of organic matter to promote bio-heat and evaporation of water, thus reducing leachate production under suitable ventilation conditions. Carbohydrates and amino acids were the main energy metabolism sources of bacteria during the landfill process. This study deepens our understanding of the leachate reduction mechanism in the micro-aerobic landfill.

The Potential of Spent Coffee Grounds @ MOFs Composite Catalyst in Efficient Activation of PMS to Remove the Tetracycline Hydrochloride from an Aqueous Solution

The efficient removal of Tetracycline Hydrochloride (TC) from wastewater, which is a difficult process, has attracted increasing attention. Aiming to synchronously achieve the goal of natural waste utilization and PMS activation, we have combined the MOFs material with waste coffee grounds (CG). The catalytic activity of the CG@ZIF-67 composite in the TC removal process was thoroughly evaluated, demonstrating that the TC removal rate could reach 96.3% within 30 min at CG@ZIF-67 composite dosage of 100 mg/L, PMS concertation of 1.0 mM, unadjusted pH 6.2, and contact temperate of 293.15 K. The ¹O₂ and ·SO₄^- in the CG@ZIF-67/PMS/TC system would play the crucial role in the TC degradation process, with ¹O₂ acting as the primary ROS. The oxygen-containing functional groups and graphite N on the surface of CG@ZIF-67 composite would play a major role in efficiently activating PMS and correspondingly degrading TC. In addition, the CG@ZIF-67/PMS/TC system could withstand a wide pH range (3-11). The application of CG in preparing MOF-based composites will provide a new method of removing emerging pollutants from an aqueous solution.

New method for morphological identification and simultaneous quantification of multiple tetracyclines by a white fluorescent probe

The threat of tetracycline antibiotics to the environment and human health is attracting widespread attention. The development of morphological analysis and quantitative techniques of multiple tetracyclines is of great significance for the evaluation of biochemical toxicity, wide-spectrum antibacterial property and degradation cycle between different tetracyclines. In this study, the white fluorescent Eu/Tb@CDs was synthesized and applied successfully to the identification and detection of the most widely used tetracycline antibiotics (tetracycline (TC), oxytetracycline (OC), chlortetracycline (CC) and doxycycline (DC)) with detection limits all below 1 nM. For the actual water samples with coexistence of the above 4 tetracyclines, their simultaneous morphology identification and accurate quantitative detection can also be realized through simple spectrometric measurement. In addition, the selective and competitive experiments have been carried out on the pollutants widely present in water, and the results have also confirmed that other pollutants could not interfere with the detection of the above 4 tetracyclines. It is undeniable that this work will conveniently and visually reveal the existence information and geographical distribution characteristics of different tetracycline antibiotics in the environment and their action mechanism on organisms.

Enhanced adsorption capacity of tetracycline on porous graphitic biochar with an ultra-large surface area†

Excessive tetracycline in the water environment may lead to the harming of human and ecosystem health. Removing tetracycline antibiotics from aqueous solution is currently a most urgent issue. Porous graphitic biochar with an ultra-large surface area was successfully prepared by a one-step method. The effects of activation temperature, activation time, and activator dosage on the structural changes of biochar were investigated by scanning electron microscopy, Brunauer–Emmett–Teller, X-ray powder diffraction, and Raman spectroscopy. The effect of the structure change, adsorption time, temperature, initial pH, and co-existing ions on the tetracycline removal efficiency was also investigated. The results show that temperature had the most potent effect on the specific surface area, pore structure, and extent of graphitization. The ultra-large surface area and pore structure of biochar are critical to the removal of tetracycline. The q_e of porous graphitic biochar could reach 1122.2 mg g⁻¹ at room temperature. The calculations of density functional theory indicate that π–π stacking interaction and p–π stacking interaction can enhance the tetracycline adsorption on the ultra-large surface area of graphitic biochar.

1. A ultra-large surface area of porous graphitic biochar was successfully using corn starch and ZnCl₂ by a one-step method. 2. The adsorption capacity of tetracycline on the biochar could get 1122.2 mg g⁻¹ at room temperature.

Chemical modification of biochars as a method to improve its surface properties and efficiency in removing xenobiotics from aqueous media

Biochar (BC) is a carbonaceous material produced by pyrolysis of biomass, applied in various areas such as water purification, fuel production, soil amendment, etc. Many types of BC are characterized by insufficient textural parameters or poor surface chemistry, and hence by low adsorption capacity. This makes innovative chemical methods increasing BC ability to remove xenobiotics from aquatic environments highly needed. Many of them have already been described in the literature. This review presents them in detail and evaluates their effectiveness in improving textural parameters, surface chemistry, and adsorption capacity of BC.

Screening of new adsorbents to remove algal organic matter from aqueous solutions: kinetic analyses and reduction of disinfection by-products formation

The algal organic matter (AOM) is a problem in water treatment. Although the adsorption process is extensively applied to drinking water treatment, little information is known about the potential of new adsorbents to remove AOM. Herein, this work evaluated the removal of AOM and its main compounds (dissolved organic carbon (DOC), carbohydrate, and protein) by new adsorbents-mesoporous silica (SBA-16), graphene oxide material from citric acid (CA), and sugar (SU), and a composite of CA immobilized on sand (GSC). In general, the removal efficiencies followed the order of SBA-16 > CA > SU or GSC for DOC, carbohydrate, and protein. At environmental condition (5 mg DOC·L^-1 and pH 8), high removals were reported for SBA-16 (88.8% DOC, 80.0% carbohydrate, and 99.6% protein) and CA (70.0% DOC, 66.7% carbohydrate, and 89.7% protein), while moderate removals were found for SU (60.5% DOC, 47.9% carbohydrate, and 66.5% protein) and GSC (67.4% DOC, 60.8% carbohydrate, and 57.4% protein). Based on these results, further analyses were done with SBA-16 and CA. Both adsorbents' efficiencies decayed with the pH increment of the test water. Disinfection by-products reductions found using SBA-16 - trihalomethanes (58.2 to 94.7%) and chloral hydrate (48.7 to 78.8%) - were higher than the ones using CA-trihalomethanes (45.2 to 82.4%) and chloral hydrate (40.1 to 70.8%). This study showed the potential of applying these adsorbents for AOM removal, and further investigations are suggested to increase the adsorption capacity of these adsorbents.

Potential Application of Discarded Natural Coal Gangue for the Removal of Tetracycline Hydrochloride (TC) from an Aqueous Solution

The generation and accumulation of discarded coal gangue (CG) have severe environmental impacts. CG can adsorb other pollutants in the aquatic environment. However, previous studies have not assessed whether CG can adsorb the emerging contaminant tetracycline hydrochloride (TC). Here, discarded CG taken from a mine was pretreated by crushing, cleaning, and sieving and subsequently applied to the adsorption of TC. The adsorption studies were carried out by batch equilibrium adsorption experiments. Our findings indicated that the adsorption behavior could be accurately described using the quasi-first order kinetic and Langmuir adsorption isotherm models, indicating that monolayer adsorption was the main mechanism mediating the interaction between CG and TC. The adsorption process was classified as a thermodynamic endothermic and spontaneous reaction, which was controlled by chemical and physical adsorption, including electrostatic interaction and cation exchange. The pH of the solution had a great influence on the TC adsorption capacity of GC, with higher adsorption occurring in acidic environments compared to alkaline environments. This was attributed to the changes in CG Zeta potential and TC pKa at different pH conditions. Collectively, our findings demonstrated the potential applicability of discarded CG for the adsorption of TC and provided insights into the adsorption mechanisms.

Recent Advances in Carbon-Based Materials for Adsorptive and Photocatalytic Antibiotic Removal

Antibiotics have been a primary environmental concern due to their widespread dispersion, harmful bioaccumulation, and resistance to mineralization. Unfortunately, typical processes in wastewater treatment plants are insufficient for complete antibiotic removal, and their derivatives in effluent can pose a threat to human health and aquatic communities. Adsorption and photocatalysis are proven to be the most commonly used and promising tertiary treatment methods. Carbon-based materials, especially those based on graphene, carbon nanotube, biochar, and hierarchical porous carbon, have attracted much attention in antibiotic removal as green adsorbents and photocatalysts because of their availability, unique pore structures, and superior physicochemical properties. This review provides an overview of the characteristics of the four most commonly used carbonaceous materials and their applications in antibiotic removal via adsorption and photodegradation, and the preparation of carbonaceous materials and remediation properties regarding target contaminants are clarified. Meanwhile, the fundamental adsorption and photodegradation mechanisms and influencing factors are summarized. Finally, existing problems and future research needs are put forward. This work is expected to inspire subsequent research in carbon-based adsorbent and photocatalyst design, particularly for antibiotics removal.

Role of multistage inoculation on the co-composting of food waste and biogas residue

Effect of diverse Lactobacillus amylophilus, Geobacillus thermoleovorans, and Bacillus subtilis inoculation patterns on the co-composting performance of food waste and biogas residue was explored. Experimental results revealed that, compared to the single-stage inoculation and non-inoculation groups, the multistage inoculation pattern prolonged the thermophilic period during composting, consequently improving organic matter decomposition and humification [with a high germination index (120.9%)]. In addition, it could promote the development of humic substances [with a high humus index (4.3) and biological index (1.4)] and lower emissions of carbon dioxide (CO₂), methane (CH₄), and ammonia (NH₃). Additionally, it could improve the microbial variety and the amounts of functional bacteria (i.e., Chloroflexi) in compost, which might be advantageous for the decomposition of refractory organic materials and plant growth. Therefore, the multistage inoculation pattern is recommended for organic waste composting in terms of its gas emissions, compost quality and efficacy benefits.

Improved Adsorption of Tetracycline in Water by a Modified Caulis spatholobi Residue Biochar

A potassium modified biochar (KBC) using Caulis spatholobi residue as the raw material was prepared by adopting a two-step method of pyrolysis followed by high-temperature potassium hydroxide activation, and its properties were characterized. Activation using potassium hydroxide under high temperature induced the loss of CaCO₃ and partial C on biochar, which created a high specific surface area (1336.31 m²/g) together with a developed pore structure. pH displayed a slight influence on tetracycline adsorption, which signified the slight influence of the existence of tetracycline and the charge potential of biochar. Besides, pore filling, hydrogen bonding and π-π EDA stacking interactions possibly resulted in tetracycline adsorption on biochar. Tetracycline adsorption was fast in the original period, followed by a slower rate of adsorption until equilibrium was reached. Adsorption kinetics of tetracycline could be described using secondary and Elovich kinetic models. Adsorption isotherms for tetracycline were well fitted to the Langmuir isotherm model, and the maximum adsorption capacity of KBC was 830.78 mg/g at 318 K. According to a study of the thermodynamics, the adsorption of tetracycline on KBC was an endothermic reaction process. Corresponding results in the present study demonstrated that high-temperature potassium hydroxide activation enabled biochar to effectively eliminate tetracycline from water and wastewater.

Biodrying of biogas residue through a thermophilic bacterial agent inoculation: Insights into dewatering contribution and microbial mechanism

Biogas residue (BR) is difficult to transport and compost due to its high moisture content. The purpose of this study was to elucidate the dewatering and microbial mechanisms underlying the inoculation of a thermophilic bacterial agent (TBA) onto BR with a high moisture content (i.e., 90.4%). TBA accounted for 78.7% of the water loss rate in BR, dramatically higher than the effects of aeration, external heat, or indigenous microorganisms (i.e., 1.8%, 0.1%, and 19.4%, respectively). Furthermore, TBA inoculation resulted in a stable product [with a low moisture content (9.4%) and a high seed germination index (107.3%)]. Finally, TBA increased microbial diversity and the abundance of functional bacteria (Proteobacteria and Bacteroidota), which might be beneficial for refractory organic compound decomposition and plant growth. Thus, biodrying BR via inoculation with a TBA is recommended economically.