Treatment of distiller grain with wet-process phosphoric acid leads to biochar for the sustained release of nutrients and adsorption of Cr(VI)

A Comprehensive Review of Lab-Scale Studies on Removing Hexavalent Chromium from Aqueous Solutions by Using Unmodified and Modified Waste Biomass as Adsorbents

Anthropogenic activities and increasing human population has led to one of the major global problems of heavy metal contamination in ecosystems and to the generation of a huge amount of waste material biomass. Hexavalent chromium [Cr(VI)] is the major contaminant introduced by various industrial effluents and activities into the ecosystem. Cr(VI) is a known mutagen and carcinogen with numerous detrimental effects on the health of humans, plants, and animals, jeopardizing the balance of ecosystems. Therefore, the remediation of such a hazardous toxic metal pollutant from the environment is necessary. Various physical and chemical methods are available for the sequestration of toxic metals. However, adsorption is recognized as a more efficient technology for Cr(VI) remediation. Adsorption by utilizing waste material biomass as adsorbents is a sustainable approach in remediating hazardous pollutants, thus serving the dual purpose of remediating Cr(VI) and exploiting waste material biomass in an eco- friendly manner. Agricultural biomass, industrial residues, forest residues, and food waste are the primary waste material biomass that could be employed, with different strategies, for the efficient sequestration of toxic Cr(VI). This review focuses on the use of diverse waste biomass, such as industrial and agricultural by-products, for the effective remediation of Cr(VI) from aqueous solutions. The review also focuses on the operational conditions that improve Cr(VI) remediation, describes the efficacy of various biomass materials and modifications, and assesses the general sustainability of these approaches to reducing Cr(VI) pollution.

A new approach to explore and assess the sustainable remediation of chromium-contaminated wastewater by biochar based on 3E model

As a cost-effective material, biochar, known as 'black gold', has been widely used for environmental applications (EA), including chromium-contaminated wastewater remediation. However, limited reports focused on the multiple impacts of biochar, including energy consumption (EC) and environmental risk (ER). Hence, to recommend biochar as a green material for sustainable development, the three critical units were explored and quantitatively assessed based on an adapted 3E model (EA-EC-ER). The tested biochar was produced by limited-oxygen pyrolysis at 400-700 °C by using three typical biomasses (Ulva prolifera, phoenix tree, and municipal sludge), and the optimal operational modulus of the 3E model was identified using six key indicators. The findings revealed a significant positive correlation between EC and biochar yield (p < 0.05). The biochar produced by phoenix tree consumed more energy due to having higher content of unstable carbon fractions. Further, high-temperature and low-temperature biochar demonstrated different chromium removal mechanisms. Notably, the biochar produced at low temperature (400 °C) achieved better EA due to having high removal capacity and stability. Regarding ER, pyrolysis temperature of 500 °C could effectively stabilize the ecological risk in all biochar and the biochar produced by Ulva prolifera depicted the greatest reduction (37-fold). However, the increase in pyrolysis temperature would lead to an increase in global warming potential by nearly 22 times. Finally, the 3E model disclosed that the biochar produced by Ulva prolifera at 500 °C with low EC, high EA, and low ER had the most positive recommendation index (+78%). Importantly, a rapid assessment methodology was established by extracting parameters from the correlation. Based on this methodology, about eight percent of biochar can be the highest recommended from more than 100 collected peer-related data. Overall, the obtained findings highlighted that the multiple impacts of biochar should be considered to efficiently advance global sustainable development goals.

The application of P-modified biochar in wastewater remediation: A state-of-the-art review

Phosphorus modified biochar (P-BC) is an effective adsorbent for wastewater remediation, which has attracted widespread attention due to its low cost, vast source, unique surface structure, and abundant functional groups. However, there is currently no comprehensive analysis and review of P-BC in wastewater remediation. In this study, a detailed introduction is given to the synthesis method of P-BC, as well as the effects of pyrolysis temperature and residence time on physical and chemical properties and adsorption performance of the material. Meanwhile, a comprehensive investigation and evaluation were conducted on the different biomass types and phosphorus sources used to synthesize P-BC. This article also systematically compared the adsorption efficiency differences between P-BC and raw biochar, and summarized the adsorption mechanism of P-BC in removing pollutants from wastewater. In addition, the effects of P-BC composite with other materials (element co-doping, polysaccharide stabilizers, microbial loading, etc.) on physical and chemical properties and pollutant adsorption capacity of the materials were investigated. Some emerging applications of P-BC were also introduced, including supercapacitors, CO2 adsorbents, carbon sequestration, soil heavy metal remediation, and soil fertility improvement. Finally, some valuable suggestions and prospects were proposed for the future research direction of P-BC to achieve the goal of multiple utilization.

Adsorption effect and mechanism of Cd(II) by different phosphorus-enriched biochars

The resource utilization of agricultural and forestry waste, especially the high-value transformation of low-grade phosphate rock and derivatives, is an important way to achieve sustainable development. This study focuses on the impregnation and co-pyrolysis of rice straw (RS) with fused calcium magnesium phosphate (FMP), FMP modified with citric acid (CA-FMP), and calcium dihydrogen phosphate (MCP) to produce three phosphorous-enriched biochars (PBC). The Cd(II) removal efficiency of biochars before and after phosphorus modification was investigated, along with the adsorption mechanism and contribution of biochars modified with different phosphorus sources to Cd(II) adsorption. The result indicated that CA-FMP and MCP could be more uniformly loaded onto biochar, effectively increasing the specific surface area (SSA) and total pore volume. The adsorption of Cd(II) onto PBC followed a mono-layer chemisorption process accompanied by intraparticle diffusion. The adsorption of Cd(II) by PBC involved ion exchange, mineral precipitation, complexation with oxygen-containing functional groups (OFGs), cation-π interaction, electrostatic interaction, and physical adsorption. Ion exchange was identified as the primary adsorption mechanism for Cd(II) by BC and FBC (51.53% and 53.15% respectively), while mineral precipitation played a major role in the adsorption of Cd(II) by CBC and MBC (51.10% and 47.98% respectively). Moreover, CBC and MBC significantly enhanced the adsorption capacity of Cd(II), with maximum adsorption amounts of 128.1 and 111.5 mg g-1 respectively.

Surge of native rare taxa in tailings soil induced by peat bacterial invasion

The pivotal role of the native bacterial community in maintaining soil health, particularly in degraded tailings environments, is often overlooked. This study utilized peat, rich in microorganisms, to investigate its impact on soil function and native bacteria response in copper tailings-soil. Through 16S rRNA gene sequencing, changes in nutrient cycling, organic matter decomposition, and microbial activity were assessed post one-year peat remediation. Results from FEAST and cluster analysis revealed that peat-derived species disproportionately influenced tailings microbial community remediation, supported by the microbial invasion theory. Tailings responded positively to these species, with optimal function achieved at 5 % peat dosage. Peat biomarkers (Actinobacteriota, Bacteroida, Chloroflexi, and Firmicutes) played key roles in heavy metal removal and nutrition fixation. The Random Forest model and co-occurrence network highlighted contributions from native rare species (Dependentiae and Latescibacterota) activated by peat addition. These insights underscore the resilience of rare taxa and provide a foundation for soil health restoration in tailings areas. By emphasizing the importance of peat as a potential exogenous solution for activating indigenous microbial functions, these findings offer valuable insights for developing effective and sustainable remediation strategies in mining-affected regions.

Cr(VI) and doxorubicin adsorptive capture by a novel bionanocomposite of Ti-MOF@TiO2 incorporated with watermelon biochar and chitosan hydrogel

Biodegradable polymers, biochars and metal organic frameworks (MOFs) have manifested as top prospects for elimination of harmful pollutants. In the current study, Ti-MOF was synthesized and decorated with TiO2 nanoparticles, then embedded into watermelon peel biochar and functionalized with chitosan hydrogel to produce Ti-MOF@TiO2@WMPB@CTH. Various instruments were employed to assure the effective production of the bionanocomposite. The HR-TEM and SEM studies referred to excellent surface porosity and homogeneity of Ti-MOF@TiO2@WMPB@CTH bionanocomposite, with 51.02-74.23 nm. Based on the BET analysis, the mesoporous structure has a significant surface area of 366.04 m2 g-1 and a considerable total pore volume of 11.38 × 10-2 cm3 g-1, with a mean pore size of 12.434 nm. Removal of doxorubicin (DOX) and hexavalent chromium (Cr(VI)) was examined under various experimentations. Pseudo-second order kinetic models in addition to Langmuir isotherm offered the best fitting. Thermodynamic experiments of the two contaminants demonstrated spontaneous and endothermic interactions. After five subsequent adsorption and desorption cycles, Ti-MOF@TiO2@WMPB@CTH bionanocomposite demonstrated an exceptional recyclability for the elimination of DOX and Cr(VI) ions, reaching 97.96 % and 95.28 %, respectively. Finally, the newly designed Ti-MOF@TiO2@WMPB@CTH bionanocomposite demonstrated a high removing efficiency of Cr(VI) ions and DOX from samples of real water.

Modification of biochar by phosphoric acid via wet pyrolysis and using it for adsorption of methylene blue

Algae biochar (ABC), coconut shell biochar (CSBC), and coconut coat biochar (CCBC) were prepared by wet pyrolysis in a phosphoric acid solvent under normal pressure. Materials were characterized for their micromorphology, specific surface area, and surface functional groups by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption spectrum technique and Fourier transform infrared diffraction (FT-IR). The evaluation of the liquid-phase adsorption performance using methylene blue (MB) as a pigment model, and the effects of temperature, pH, adsorbent dosage, and pollutant concentration of the MB adsorption onto modified biochars were fully investigated. The adsorption mechanism was proposed based on the adsorption kinetics curve and adsorption isotherm. The synthetic biochar showed great adsorption properties toward cationic dyes rather than anionic dyes. Specifically, the adsorption abilities for algal biochar, coconut shell biochar, and coconut coat biochar were determined to be 97.5%, 95.4% and 21.2%, respectively. The isothermal adsorption of MB by the three kinds of biochar conformed to the Langmuir equation, and the adsorption process fitted to the quasi-second-order kinetic equation, which suggested that ABC and CSBC effectively adsorbed MB dye molecules through hydrogen bonding, π-π stacking, and electrostatic interactions.

Potassium assisted pyrolysis of Chinese Baijiu distillers' grains to prepare biochar as controlled-release K fertilizer

A novel K-loaded biochar as controlled-release K fertilizer was prepared through K assisted pyrolysis of distillers' grains (DGs, typical solid-byproducts of Chinese Baijiu) under different atmospheres (N₂ and CO₂) and temperatures (400 and 800 °C). The fabricated DGs-based biochar exhibited high K loading (200.20-232.33 mg/g), and the release kinetics and column leaching experiments suggested that K-loaded biochar exhibited excellent controlled release performance in a long term. Compared with other biochar, the K-loaded biochar prepared at CO₂ and 400 °C has lower cumulative release ratio of 82.35 %, and could retain the durative K release at ~0.5 % for 25 d. The release kinetics suggested that the K release behavior was dominated by dissolution, electrostatic attraction, adsorption, confinement effect, and chemical interaction. Furthermore, pot experiments revealed that K-loaded biochar could promote the growth of Komatsuna, in which the fresh weight and chlorophyll relative content of Komatsuna cultivated with biochar prepared at CO₂ and 400 °C reached 0.146 g and 41.95 after 25 d growth, respectively. The above results suggested that the K-loaded biochar exhibited excellent utilization potential as a controlled-release K fertilizer, facilitating the sustainable development and resource valorization of Baijiu industry.

Transformation of phosphorus species during phosphoric acid-assisted pyrolysis of lignocellulose

Phosphoric acid-assisted pyrolysis (PAAP) is a pyrolysis technique with potential for the engineered and environmental application. Nevertheless, the volatilisation, immobilisation, and dissolution of phosphorus (P) species have been neglected during PAAP of lignocellulose. Therefore, we compared the transformation of P species with direct-pyrolysis and PAAP system, using multiple techniques including gas chromatography tandem mass spectrometry (GCMS) and ³¹P nuclear magnetic resonance (NMR). It was also investigated that the properties of pyrogenic and modified carbons obtained from lignocellulose pyrolysis at 200-650 °C. As the temperature increased, volatile P species evolved into gas-phase during PAAP, inhibiting the formation of the macromolecular volatile components. Compared with pyrogenic carbons, modified carbons with more aromatic structures experienced a higher degree of dehydration and cyclisation via catalytic crosslinking reaction. PAAP system facilitated more generation of persistent free radical (PFR) below 500 °C and the attenuation of PFR signals was observed at 500-650 °C, which may be associated with the sequestration and elimination of P species between carbon matrix. Notably, three configurations of C₃PO, CPO, and COP were the major combinations of P and C elements on modified carbons. Increased gaseous P and decreased soluble P were observed with elevated temperatures in PAAP system. The species proportion of immobilised P clearly demonstrated the transformation of partial P species from inorganic to organic through pyrolysis. The immobilised P could serve as a potential sustained-release source participating in P biogeochemical cycles. These findings are fundamental for the technical design of lignocellulose pyrolysis.

Closing the Nutrient Loop-The New Approaches to Recovering Biomass Minerals during the Biorefinery Processes

The recovery of plant mineral nutrients from the bio-based value chains is essential for a sustainable, circular bioeconomy, wherein resources are (re)used sustainably. The widest used approach is to recover plant nutrients on the last stage of biomass utilization processes-e.g., from ash, wastewater, or anaerobic digestate. The best approach is to recover mineral nutrients from the initial stages of biomass biorefinery, especially during biomass pre-treatments. Our paper aims to evaluate the nutrient recovery solutions from a trans-sectorial perspective, including biomass processing and the agricultural use of recovered nutrients. Several solutions integrated with the biomass pre-treatment stage, such as leaching/bioleaching, recovery from pre-treatment neoteric solvents, ionic liquids (ILs), and deep eutectic solvents (DESs) or integrated with hydrothermal treatments are discussed. Reducing mineral contents on silicon, phosphorus, and nitrogen biomass before the core biorefinery processes improves processability and yield and reduces corrosion and fouling effects. The recovered minerals are used as bio-based fertilizers or as silica-based plant biostimulants, with economic and environmental benefits.