Biomass as source for hydrochar and biochar production to recover phosphates from wastewater: A review on challenges, commercialization, and future perspectives

Characteristics and phytotoxicity of hydrochar-derived dissolved organic matter: Effects of feedstock type and hydrothermal temperature

The dissolved organic matter (DOM) with high mobility and reactivity plays a crucial role in soil. In this study, the characteristics and phytotoxicity of DOM released from the hydrochars prepared from different feedstocks (cow manure, corn stalk and Myriophyllum aquaticum) under three hydrothermal carbonization (HTC) temperatures (180, 200 and 220°C) were evaluated. The results showed that the hydrochars had high dissolved organic carbon content (20.15 to 37.65 mg/g) and its content showed a gradual reduction as HTC temperature increased. Three fluorescent components including mixed substance of fulvic acid-like and humic acid-like substances (C1, 30.92%-58.32%), UVA humic acid-like substance (C2, 25.27%-29.94%) and protein-like substance (C3, 11.74%-41.92%) were identified in hydrochar DOM by excitation emission matrix spectra coupled with parallel factor analysis. High HTC temperature increased the relative proportion of aromatic substances (C1+C2) and humification degree of hydrochar DOM from cow manure, while it presented adverse effects on the hydrochar DOM from corn stalk and Myriophyllum. aquaticum. The principal component analysis suggested that feedstock type and HTC temperature posed significant effects on the characteristics of hydrochar DOM. Additionally, seed germination test of all hydrochar DOM demonstrated that the root length was reduced by 8.88%-26.43% in contrast with control, and the germination index values were 73.57%-91.12%. These findings provided new insights into the potential environmental effects for hydrochar application in soil.

Hydrochar as a bio-based adsorbent for heavy metals removal: A review of production processes, adsorption mechanisms, kinetic models, regeneration and reusability

The spread of heavy metals throughout the ecosystem has extremely endangered human health, animals, plants, and natural resources. Hydrochar has emerged as a promising adsorbent for removal of heavy metals from water and wastewater. Hydrochar, obtained from hydrothermal carbonization of biomass, owns unique physical and chemical properties that are highly potent in capturing heavy metals via surface complexation, electrostatic interactions, and ion exchange mechanisms. This review focuses on removing heavy metals by hydrochar adsorbents from water bodies. The article discusses factors affecting the adsorption capacity of hydrochars, such as contact time, pH, initial metal concentration, temperature, and competing ions. Literature on optimization approaches such as surface modification, composite development, and hybrid systems are reviewed to enlighten mechanisms undertaking the efficiency of hydrochars in heavy metals removal from wastewater. The review also addresses challenges such as hydrochar regeneration and reusability, alongside potential issues related to its disposal and metal leaching. Integration with current water purification methods and the significance of ongoing research and initiatives promoting hydrochar-based technologies were also outlined. The article concludes that combining hydrochar with modern technologies such as nanotechnology and advanced oxidation techniques holds promise for improving heavy metal remediation. Overall, this comprehensive analysis provides valuable insights to guide future studies and foster the development of effective, affordable, and environmentally friendly heavy metal removal technologies to ensure the attainment of safer drinking water for communities worldwide.

Biochar-enhanced bioremediation of eutrophic waters impacted by algal blooms

The permanent problem of formation of algal blooms in water polluted with nitrogen and phosphorus is one of the formidable environmental problems. Biochar has the potential to solve the issues related to eutrophication due to its special structure and ability to absorb the nutrients. Biochar's exceptional nutrient absorption capacity allows it to absorb excess nutrients, causing the algae to use fewer nutrients. This review deals with effective performance of biochar in reducing the effects caused by algal blooms and improving the environmental conditions. Besides, an analysis of the issues involved addresses the origins and consequences of nitrogen and phosphorus pollution, and the formation of algal blooms is also reviewed. It then delves deeply into biochar, explaining its properties, production methods, and their uses in environmental contexts. The review emphasizes that biochar can be effective in dealing with many challenges associated with environments affected by algal blooms, specifically focusing on the positive effects of biochar and algae to examine their roles in controlling algae growth. Finally, the review emphasizes new achievements and innovative ideas to foster sustainable aquatic ecosystems. The discussions emphasize the central role of biochar in managing nutrient-rich waters and algal blooms.

Recent advances in environmental and agricultural applications of hydrochars: A review

Hydrochar is a carbonaceous material that is generated through the process of hydrothermal carbonization (HTC) from biomass, which has garnered considerable attention in recent years owing to its potential applications in a diverse range of fields, such as environmental remediation and agriculture. Hydrochar is produced from a diverse range of biomass waste materials and retains exceptional properties, including high carbon content, stability, and surface area, making it an optimal candidate for various enviro-agricultural applications. Moreover, it delves into the production process of hydrochar, with explicit emphasis on the optimization of certain properties during the production of hydrochar from bio-waste. Furthermore, the potential of hydrochar as an adsorbent and catalyst support for heavy metals and dyes was extensively explored, along with a soil remediation potential that can improve the physical, chemical and biological properties of soil. This comprehensive review aims to provide a thorough overview of hydrochar with a particular focus on its production, properties, and prospective applications. The significance of hydrochar is accentuated and the growing need for alternative sources of energy and materials that are environmentally sustainable is highlighted in this paper. Besides, the consequence of hydrochar on soil properties such as water-holding capacity, nutrient retention, and total soil porosity, as well as its influence on soil chemical properties such as cation exchange capacity, electrical conductivity, and surface functionality is scrutinized.

Conversion of locally available materials to biochar and activated carbon for drinking water treatment

For environmental sustainability and to achieve sustainable development goals (SDGs), drinking water treatment must be done at a reasonable cost with minimal environmental impact. Therefore, treating contaminated drinking water requires materials and approaches that are inexpensive, produced locally, and effortlessly. Hence, locally available materials and their derivatives, such as biochar (BC) and activated carbon (AC) were investigated thoroughly. Several researchers and their findings show that the application of locally accessible materials and their derivatives are capable of the adsorptive removal of organic and inorganic contaminants from drinking water. The application of locally available materials such as lignocellulosic materials/waste and its thermo-chemically derived products, including BC and AC were found effective in the treatment of contaminated drinking water. Thus, this review aims to thoroughly examine the latest developments in the use of locally accessible feedstocks for tailoring BC and AC, as well as their features and applications in the treatment of drinking water. We attempted to explain facts related to the potential mechanisms of BC and AC, such as complexation, co-precipitation, electrostatic interaction, and ion exchange to treat water, thereby achieving a risk-free remediation approach to polluted water. Additionally, this research offers guidance on creating efficient household treatment units based on the health risks associated with customized adsorbents and cost-benefit analyses. Lastly, this review work discusses the current obstacles for using locally accessible materials and their thermo-chemically produced by-products to purify drinking water, as well as the necessity for technological interventions.

Municipal sludge biochar skeletal sodium alginate beads for phosphate removal

A novel Fe/La decorative biochar filled in sodium alginate beads (SA-KBC-Fe/La) was prepared by a simple sol-gel method and applied to adsorb phosphate (P) efficiently from water in this study. The morphology, structure and chemical component of the hydrogel beads were characterized in detail. And the synthesized bead exhibited easy separation and high P uptake of 46.65 mg/g when the Fe: La was of 1: 2 at 298 K with initial P of 100 mg/L, which was much higher than SA gel bead. The adsorption showed that the optimal pH was 6, and the adsorption was met with pseudo-second-order kinetics and Langmuir isothermal models, indicating a chemical adsorption process. The adsorption capacity remained 82 % after 5 cycles of adsorption. The adsorption mechanism of P was mainly of ligand exchange and electrostatic attraction. Compared with other reported adsorbents, the modification of Fe/La could enhance the mechanical property of SA-KBC-Fe/La beads with increasing active sites. Additionally, the involved biochar could lead to excellent thermal stability and hierarchical porous structure of beads with larger specific surface area (54.22 m2/g). The study could provide new ideas for P removal and strategy for the final disposal of municipal sludge.

Restricted reaction of layered double hydroxide nanoparticles with phosphate in a confined microsphere space

Over the past decades, considerable efforts have been made to find useful solutions for phosphate pollution control. The state transition of nanomaterials from freely dispersed to encapsulated provides a realizable route for their application in phosphate elimination. The separation convenience offered by encapsulation has been widely recognized, however, the unique binding mode of nanostructures and phosphate in the confined space remains unclear, limiting its further development. Here, carboxymethyl cellulose (CMC) microspheres were used as hosts to deploy layered double hydroxide (LDH) nanoparticles. On this basis, we described an attempt to explore the adsorption behavior of LDH and phosphate in the microsphere space. Compared to their freely dispersed analogues, LDH particles exhibited higher structural stability, wider pH adaptability, and better phosphate selectivity when spatially confined in the CMC microsphere. Nevertheless, the kinetic process was severely inhibited by three orders of magnitude. Besides, the saturated phosphate adsorption capacity was also reduced to 74.6 % of the freely dispersed system. A combinative characterization revealed that the highly electronegative CMC host not only causes electrostatic repulsion to phosphate, but also extracts the electron density of the metal center of LDH, weakening its ability to act as a Lewis acid site for phosphate binding. Meanwhile, the microsphere encapsulation also hinders the ion exchange function of interlayer anions and phosphate. This study offers an objective insight into the reaction of LDH and phosphate in the confined microsphere space, which may contribute to the advanced design of encapsulation strategies for nanoparticles.

Lab-scale engineered hydrochar production and techno-economic scaling-up analysis

Despite the extensive use of engineered hydrochar (EHC) for contaminants adsorption in water, little is known about the scaling-up of EHC production which has kept the technology at a low readiness level (TRL). Full-scale EHC production was simulated to help bridge this knowledge gap. A systematic analysis was performed where EHC was produced from rice straw using hydrothermal carbonization (HTC) at 200 °C with iron addition. A techno-economic evaluation model was employed to simulate the production process and to estimate energy requirements, configuration, and cost scenarios for the HTC process. The minimum selling price (MSP) analysis of the engineered hydrochar was found to be almost half compared to the market price for other similar sorbents ($ 76/t vs. $136/t) suggesting that EHC production is feasible for scaling up. Finally, as a trial, the resulting material was tested for its efficacy in the adsorption of an anionic organic contaminant (e.g., Congo Red, C32H22N6Na2O6S2) in water to identify its potential for water treatment. Experimental results showed that EHC adsorbed > 95% CR suggesting significant adsorption capability and feasibility for production scale-up.

Performance of novel Ca-biocomposites produced from banana peel and eggshell for highly efficient removal and recovery of phosphate from domestic wastewater

Using biowaste-based adsorbents to remove phosphorus (P) from wastewater offers significant benefits concerning eutrophication mitigation and addressing waste management challenges. In this work, Ca-biocomposites were prepared by pyrolysis (700 °C) of a mixture of banana peel (BP) and eggshell (ES). The mass ratio of BP to ES was varied in 2:1, 1:1, and 1:2 ratios. Among the tested mixtures, the BPES-1:2 sample exhibited excellent P removal performance, reaching a maximum P adsorption capacity (Qmax) of 214 ± 5 mg P/g. The adsorption process fitted well with the Avrami order kinetic model (R2 > 0.996) and the Liu isotherms model (R2 > 0.997). The excellent fit of the experimental data to the Avrami model suggests that chemisorption is the dominant interaction mechanism, leading to precipitation through the formation of calcium phosphates. Additionally, the Liu model anticipates that the energetic characteristics of the adsorbent's active sites cannot be identical. This is in agreement with the presence of Ca(OH)2 and CaCO3 in the adsorbent material, where the Ca(OH)2 active sites are preferred by the adsorbate molecules (PO43-) for occupation. Furthermore, thermodynamic analysis revealed that P adsorption is a spontaneous process of exothermic nature (ΔH° < 0). The calculated activation energy for the process (72.81 kJ/mol) suggests the P adsorption mechanism involves strong chemical bonding between the adsorbent and P species. In addition, precipitation of apatite (Ca5(PO4)3OH), a vital component in fertilizer production, was observed during the adsorption process. In tertiary treated wastewater applications, the BPES-1:2 biocomposite demonstrated a P removal efficiency of 90%. The solubility of P in a 2% formic acid solution was 100%, while the water-soluble P content was measured at 5.6%. These findings highlight the product's sustainable and environmentally beneficial nature by demonstrating its potential as a slow-release fertilizer, contributing to the application of the 3R slogan: Reduce, Reuse, Recycle. This value-added product is promising in supplying nutrients to plants over an extended period while minimizing the risk of nutrients leaching into the environment.

Effect of chemical aging on phosphate adsorption and ecotoxicological properties of magnesium-modified biochar

Using magnesium-biochar composites (Mg-BC) in adsorption allows for the efficient and economically relevant removal of phosphate (PO43-) from water and wastewater. Applying Mg-BC for pollutant removal requires evaluating the adsorption capacity of composites and their ecotoxicological properties. Investigating the composite aging during the application of these composites into the soil is also essential. In the present study, nonaged and aged (at 60 or 90 °C) Mg-BC composites were investigated in the context of pyrolysis temperature (500 or 700 °C). All analyzed biochars were examined by Fourier transform infrared spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and surface area. The content of polycyclic aromatic hydrocarbons (PAHs) (bioavailable Cfree and organic solvent-extractable Ctot), heavy metals (HMs), and environmentally persistent free radicals (EPFRs) were determined. Ecotoxicity was evaluated using tests with Folsomia candida and Allivibrio fischeri. The dependence of adsorption on pyrolysis temperature and composite aging time was observed. Changes in physicochemical properties occurring as a result of aging reduced the adsorption of PO43- on Mg-BC composites. It was found that nonaged Mg-BC700 was more effective (9.55 mg g -1) in the adsorption of PO43- than Mg-BC500 (5.75 mg g-1). The adsorption capacities of aged composites were from 21 to 61% lower than those of the nonaged composites. Due to aging, the content of Cfree PAHs increased by 3-5 times depending on the pyrolysis temperature. However, aging reduced the Ctot PAHs in all composites from 24 to 35% depending on the pyrolysis temperature. Ecotoxicological evaluation of Mg-BC composites showed increased toxicity after aging to both organisms. The use of aged BC potentially increases the contaminant content and toxicity of Mg-BC composites.

Pyrolytic and hydrothermal carbonization affect the transformation of phosphorus fractions in the biochar and hydrochar derived from organic materials: A meta-analysis study

Carbonized organic materials are widely used to achieve soil improvement and alleviate soil pollution. The carbonization process significantly changes the total phosphorus (P) content and the P form in the solid phase derived from organic materials, which in turn has a significant impact on the P fertilizer effect in soils. In the present study, a meta-analysis with 278 observational data was conducted to detect the impact of the carbonization process (including pyrolytic carbonization and hydrothermal carbonization) on the transformation of P fractions in biochar or hydrochar derived from different organic materials. The results showed that the carbonization process significantly increased the total P content of the solid phase by 67.9%, and that the rate of P recovery from raw materials stayed high with a mean value of 86.8%. Among them, the impact of sludge-derived char was smaller when compared to the manure-derived char and biomass-derived char. The increase of total P in the biochar (or hydrochar) produced at >500 °C (or >200 °C) was more notable than that at <500 °C (or <200 °C). Simultaneously, the carbonization process significantly decreased the proportion of available P pool in the solid phase by 51.7% on average and increased the proportion of stable P pool in the solid phase by 204%. Appropriate production temperature helps to adjust the proportion of stable P pool in the solid phase. This meta-analysis pointed out that the carbonized solid phase recovers most of the P in the feedstock and that it promotes a significant transformation of available P pool in the feedstock to stable P in the carbonized solid phase. These findings provide useful information for the rational use of carbonization technology, the development of corresponding field management strategies, and the potential value of carbonized solid phase utilization.

Comprehensive review on lignocellulosic biomass derived biochar production, characterization, utilization and applications

Biochar is an ample source of organic carbon prepared by the thermal breakdown of biomass. Lignocellulosic biomass is a promising precursor for biochar production, and has several applications in various industries. In addition, biochar can be applied for environmental revitalization by reducing the negative impacts through intrinsic mechanisms. In addition to its environmentally friendly nature, biochar has several recyclable and inexpensive benefits. Nourishing and detoxification of the environment can be undertaken using biochar by different investigators on account of its excellent contaminant removal capacity. Studies have shown that biochar can be improved by activation to remove toxic pollutants. In general, biochar is produced by closed-loop systems; however, decentralized methods have been proven to be more efficient for increasing resource efficiency in view of circular bio-economy and lignocellulosic waste management. In the last decade, several studies have been conducted to reveal the unexplored potential and to understand the knowledge gaps in different biochar-based applications. However, there is still a crucial need for research to acquire sufficient data regarding biochar modification and management, the utilization of lignocellulosic biomass, and achieving a sustainable paradigm. The present review has been articulated to provide a summary of information on different aspects of biochar, such as production, characterization, modification for improvisation, issues, and remediation have been addressed.

Efficient low-concentration phosphate removal from sub-healthy surface water by adsorbent prepared based on functional complementary strategy

The remediation of low-concentration phosphorus polluted surface water (LP-SW) is one of most challenging environmental issues worldwide. Adsorption is more suitable for LP-SW remediation due to its low cost and operability. Based on the strategy of functional complementation among industrial solid wastes (ISWs), ISW-based phosphate absorbent material (PAM) was prepared from coal ash (CA, binder), rich‑calcium (Ca) carbide slag (CS, active component) and iron salt (functional reagent) by optimizing materials ratios and roasting conditions. PAM prepared under optimal conditions (Fe/CC-2opt) had good phosphate adsorption efficiency. Notably, Fe/CC-2opt not only ensured that the effluent met Environmental Quality Standards for Surface Water (pH = 6.0-9.0), but also facilitated the formation of brushite instead of hydroxyapatite due to FeSO4 addition. Compared with hydroxyapatite, brushite had greater potential application value as fertilizer due to its solubility and high P/Ca ratio. The possible mechanisms of phosphate adsorption by PAM included surface precipitation, surface complexation, electrostatic adsorption and release of Ca2+/OH-. Preparation cost of PAM was 80 US$/ton, and treatment cost was 0.07 US$/g P. Regeneration efficiency of PAM was still above 80 % after five cycles. The design idea and result of this study provide theoretical basis and technical support for the preparation of PAM with low cost, commercial production and great adsorption capacity.

Phosphorus Removal from Dirty Farmyard Water by Activated Anaerobic-Digestion-Derived Biochar

The management of anaerobic digestate is important to realize the value of the waste and enhance the whole system sustainability of anaerobic digestion. In this study, the phosphorus treatment of dirty irrigation water by biochar samples derived from digestate of anaerobic digestion were investigated. The biochars were further activated by steam activation with different duration time and KOH activation with different introducing ratios; the textural properties of biochars were optimized after activation from the aspect of biochar characterization. Notably, AD-N2 demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g-1. Besides the effect of biochar dosage on phosphorus removal, adsorption kinetics and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R2 = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH0 = 17.93 kJ mol-1) and spontaneous (ΔS = 96.24 J mol-1 K-1). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.

Potassium permanganate modification of hydrochar enhances sorption of Pb(II), Cu(II), and Cd(II)

Hydrochars formed by hydrothermal carbonization of hickory wood, bamboo, and wheat straw at 200 °C were modified by potassium permanganate (KMnO4) for the sorption of Pb(II), Cd(II), and Cu(II). The wheat straw hydrochar (WSHyC) modified with 0.2 M KMnO4 resulted in the most promising adsorbent (WSHyC-0.2KMnO4). Characterization of WSHyC and WSHyC-0.2KMnO4 revealed that the modified hydrochar features large specific surface area, rich of surface oxygenic functional groups (OCFG), and a significant amount of MnOx micro-particles. Batch adsorption experiments indicated that the adsorption rate by WSHyC-0.2KMnO4 was faster than for WSHyC, attaining equilibrium after around 5 h. The optimum adsorption capacity (Langmuir) of Pb(II), Cd(II), and Cu(II) by WSHyC-0.2KMnO4 was 189.24, 29.06 and 32.68 mg/g, respectively, 12 ∼ 17 times greater than by WSHyC. The significantly enhanced heavy metal adsorption can be attributable to the increased OCFG and MnOx microparticles on the surface, thereby promoting ion exchange, electrostatic interactions, and complexation mechanisms.

Comparative characterisation and phytotoxicity assessment of biochar and hydrochar derived from municipal wastewater microalgae biomass

Microalgae, originating from a tertiary treatment of municipal wastewater, is considered a sustainable feedstock for producing biochar and hydrochar, offering great potential for agricultural use due to nutrient content and carbon storage ability. However, there are risks related to contamination and these need to be carefully assessed to ensure safe use of material from wastewater microalgae. Therefore, this study compared the properties and phototoxicity of biochar and hydrochar produced via pyrolysis and hydrothermal carbonisation (HTC) of microalgae under different temperatures and residence times. While biochar promoted germination and seedling growth by up to 11.0% and 70.0%, respectively, raw hydrochar showed strong phytotoxicity, due to the high content of volatile matter. Two post-treatments, dichloromethane (DCM) washing and further pyrolysis, proved to be effective methods for mitigating phytotoxicity of hydrochar. Additionally, biochar had 35.8-38.6% fixed carbon, resulting in higher carbon sequestration potential compared to hydrochar.

Biochar production from microalgae: a new sustainable approach to wastewater treatment based on a circular economy

The generation of wastewater due to human activities are the main responsible for environmental problems. These problems are caused by the large amount of organic and inorganic pollutants related to the presence of pesticides, metals, pathogens, drugs and dyes. The photosynthetic treatment of effluents emerges as a sustainable and low-cost alternative for developing wastewater treatment systems based on a circular economy. Chemical compounds present in wastewater can be recovered and reused as a source of nutrients in microalgae cultivation to produce value-added bioproducts. The microalgal biomass produced in the cultivation with effluents has the potential to produce biochar. Biochar is carbon-rich charcoal that can be obtained by converting microalgae biomass through thermal decomposition of organic raw material under limited oxygen supply conditions. Pyrolysis, torrefaction, and hydrothermal carbonization are processes used for biochar synthesis. The application of microalgal biochar as an adsorbent material to remove several compounds present in effluents is an effective and fast treatment. This effectiveness is usually related to the unique physicochemical characteristics of the biochar, such as the presence of functional groups, ion exchange capacity, thermal stability, and high surface area, volume, and pore area. In addition, biochar can be reused in the adsorption process or applied in agriculture for soil correction. In this context, this review article describes the production, characterization, and use of microalgae biochar through a sustainable approach to wastewater treatment, emphasizing its potential in the circular economy. In addition, the article approaches the potential of microalgal biochar as an adsorbent material and its reuse after the adsorption of contaminants, as well as highlights the challenges and future perspectives on this topic.

Functional biochar fabricated from red mud and walnut shell for phosphorus wastewater treatment: Role of minerals

A novel functional biochar (BC) was prepared from industrial waste red mud (RM) and low-cost walnut shell by one facile-step pyrolysis method to adsorb phosphorus (P) in wastewater. The preparation conditions for RM-BC were optimized using Response Surface Methodology. The adsorption characteristics of P were investigated in batch mode experiments, while a variety of techniques were used to characterize RM-BC composites. The impact of key minerals (hematite, quartz, and calcite) in RM on the P removal efficiency of the RM-BC composite was studied. The results showed that RM-BC composite produced at 320 °C for 58 min, with a 1:1 mass ratio of walnut shell and RM, had a maximum P sorption capacity of 15.48 mg g^-1, which was more than double that of the raw BC. The removal of P from water was found to be facilitated significantly by hematite, which forms Fe-O-P bonds, undergoes surface precipitation, and exchanges ligands. This research provides evidence for the effectiveness of RM-BC in treating P in water, laying the foundation for future scaling-up trials.

A cradle to cradle approach towards remediation of uranium from water using carbonized arecanut husk fiber

Sustainable materials for remediation of pollutants from water is the need of the hour. In this study two carbonaceous adsorbents prepared through hydrothermal carbonisation and pyrolysis from arecanut husk fiber, an agricultural waste material were used for the adsorption of uranium from water. Batch adsorption data as interpreted using the Langmuir model showed adsorption capacities of 250 mg g^-1 and 200 mg g^-1 respectively at pH 6 for the hydrochar (AHFC) and the pyrochar (AHFT) exceeding that reported for most of the unmodified biochars. The adsorption followed pseudo-second order kinetics and was exothermic in nature. The high selectivity and excellent removal efficiencies on application to environmental ground water samples and good regeneration capacity make these sorbents promising eco-friendly materials for uranium remediation from water.

Strategies to enhance enzymatic hydrolysis of lignocellulosic biomass for biorefinery applications: A review

Global interest in lignocellulosic biorefineries has increased in the recent past due to technological advancements in sustainable and cost-effective production of numerous commodity and speciality chemicals and fuels from renewable lignocellulosic biomass (LCB). As a result, the market value of biorefinery products has also increased over the time, with an estimated worth of USD 867.7 billion by 2025. However, biorefinery operations, especially enzymatic hydrolysis, suffer from many challenges that limits the cost-effectiveness of conversion of LCB. Therefore, it is essential to understand and address these challenges in future biorefineries. The paper focuses on recent trends and challenges in enzymatic hydrolysis of LCB during lignocellulosic biorefinery operation for greener synthesis of energy, fuels, chemicals and other high-value products. Insights into the gaps in knowledge and technological challenges have also been addressed together with focus on future research needs and perspectives of enzymatic hydrolysis of LCB for biorefinery applications.

Current challenges of hydrothermal treated wastewater (HTWW) for environmental applications and their perspectives: A review

Hydrothermal treatment (HT) is an emerged thermochemical approach for the utilization of biomass. In the last decade, intense research has been conducted on bio-oil and hydrochar, during which extensive amount of hydrothermal treated wastewater (HTWW) is produced, containing large amount of organic compounds along with several toxic chemicals. The composition of HTWW is highly dependent on the process conditions and organic composition of biomass, which determines its further utilization. The current study provides a comprehensive overview of recent advancements in HTWW utilization and its properties which can be changed by varying different parameters like temperature, residence time, solid concentration, mass ratio and catalyst including types of biomasses. HTWW characterization, parameters, reaction mechanism and its application were also summarized. By considering the challenges of HTWW, some suggestions and proposed methodology to overcome the bottleneck are provided.

Impact of catalytic hydrothermal treatment and Ca/Al-modified hydrochar on lability, sorption, and speciation of phosphorus in swine manure: Microscopic and spectroscopic investigations

The effects of catalytic hydrothermal (HT) pretreatment on animal manure followed by the addition of hydrochar on the nutrients recovery have not yet been investigated using a combination of chemical, microscopic, and spectroscopic techniques. Therefore, a catalytic HT process was employed to pretreat swine manure without additives (manure-HT) and with H₂O₂ addition (manure-HT- H₂O₂) to improve the conversion efficiency of labile or organic phosphorus (P) to inorganic phase. Then, a Ca-Al layered double hydroxide hydrochar (Ca/Al LDH@HC) derived from corn cob biomass was synthesized and applied to enhance P sorption. Scanning electron microscopy (SEM), and three-dimensional excitation emission matrix (3D-EEM), X-ray photoelectron spectroscopy (XPS), P k-edge X-ray absorption near edge structure (XANES), were used to elucidate the mechanisms of P release and capture. The H₂O₂ assisted HT treatment significantly enhanced the release of inorganic P (251.4 mg/L) as compared to the untreated manure (57.2 mg/L). The 3D-EEM analysis indicated that the labile or organic P was transformed and solubilized efficiently along with the deconstruction of manure components after the H₂O₂ assisted HT pretreatment. Application of Ca/Al LDH@HC improved the removal efficiency of P from the derived P-rich HT liquid. This sorption process was conformed to the pseudo-second-order model, suggesting that chemisorption was the primary mechanism. The results of SEM and P k-edge XANES exhibited that Ca, as the dominated metal component, could act as a reaction site for the formation of phosphate precipitation. These results provide critical findings about recovering P from manure waste, which is useful for biowastes management and nutrients utilization, and mitigating unintended P loss and potential environmental risks.

Application fields of kitchen waste biochar and its prospects as catalytic material: A review

In China, a large amount of kitchen waste (KW) is generated each year, and the resource utilisation of the KW has become a problem. KW has a high carbon content and can be used as a raw material for biochar. Kitchen waste biochar (KWB) can be used to prepare adsorption materials, soil amendments, energy materials, carbon quantum dots, and electrode materials. However, few studies have used KWB as a raw material for catalytic materials. The application of sulfur (S) and nitrogen (N) doped biochar in the field of catalysis has proved effective and feasible. KWB contained a certain mass percentage of N and S elements, which has good application potential for use in the field of catalysis by KWB. In the process of preparing KWB by KW, keeping S and N as much as possible and converting them into pyridine N and thiophene S benefit the application of catalysis. This review provides a reference for the future application of KWB in China.

The Adsorption of Corn Stalk Biochar for Pb and Cd: Preparation, Characterization, and Batch Adsorption Study

Biochar adsorption emerges as a convenient and cheap treatment technology to cope with the metal pollution in wastewater. In this study, a biochar made from corn stalks was prepared and its adsorption characteristics for two heavy metals, Pb and Cd, were investigated by materials characterization and batch experiments. Biochar pyrolyzed from waste corn stalks at 400–600 °C, where biochar prepared at 600 °C (BC600) was used to perform following experiments. In materials characterization, the SEM images were initially used to reveal an obvious porous structure feature of corn stalk biochar, followed by XPS and FT-IR analyses unraveling the effects of functional groups in adsorption, especially for phenol and carboxyl groups. These functional groups provided vital adsorption sites. In batch experiment, batch experiments were conducted under different factors such as pH, temperature, and background ionic strength. The increase of pH and temperature can improve the adsorption capacity, whereas the ionic strength showed negative effects. The adsorption processes of both metals can be interpreted by fitting pseudo-first order model, as indicated in kinetic experiments, and the adsorption isotherm can be well described by the Langmuir model. Overall, this study revealed the characteristics of corn stalk biochar and deciphered the potential adsorption mechanisms.