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Plant waste (PW) is a common and abundant renewable biomass resource whose total amount is constantly increasing and accounts for up to 50% of municipal solid waste. This study aims to develop a valorization method for PW. A two-stage treatment method combining mechanical ball milling (BM) and microwave hydrothermal treatment (MHT) was investigated. BM can effectively destroy the crystallization of cellulose and reduce the particle size to increase the specific surface area and improve the MHT efficiency. The BM-MHT process could improve the 5-hydroxymethylfurfural (HMF), which is significantly higher than physical methods like grinding, ultrasonic and liquid nitrogen treatment. The BM conditions were further optimized by using a Box-Behnken Design with response surface methodology. The model showed that the highest HMF yield could reach 1.8% at 150 °C in MHT process after BM. An economic analysis indicated that BM-MHT offers a green treatment method with great economic benefits. It provides a novel valorization strategy for organic waste like PW. [Display omitted] • Ball milling can effectively depolymerize plant waste. • Ball milling combined with microwave hydrothermal treatment can valorize plant waste. • The highest yield of 5-hydroxymethylfurfural from plant waste was 1.81%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Apart from prevalent species, unique fungi (Chaetomium) dominated aerated landfill. • Fungal community structure was correlated to ammonia content in the landfill refuse. • Fungi contributed to the main nitrification (62.71 ∼ 100 %) in the absence of ammonia. • Fungi showed a stronger preference for organic nitrogen as nitrification substrate. • Fungi utilized nitrite for nitrate production with a rate 4.65 mg L−1 d−1 in SALR F. The application of in-situ aeration technology in landfills has been reported to promote fungal growth, but the community diversity and function of fungi in the aerated landfill system remain unknown. This study firstly investigated an in-situ aerated remediation landfill site to characterize the fungal community diversity in refuse. And to further reveal the fungal involvement in the nitrogen cycling system, laboratory-scale simulated aerated landfill reactors were then constructed. The results in the aerated landfill site showed a significant correlation between fungal community structure and ammonia nitrogen content in the refuse. Dominant fungi in the fungal community included commonly found environmental fungi such as Fusarium , Aspergillus , Gibberella , as well as unique fungi in the aerated system like Chaetomium. In the laboratory-scale aerated landfill simulation experiments, the fungal system was constructed using bacterial inhibitor, and nitrogen balance analysis confirmed the significant role of fungal nitrification in the nitrogen cycling process. When ammonia nitrogen was not readily available, fungi converted organic nitrogen to nitrate, serving as the main nitrification mechanism in the system, with a contribution rate ranging from 62.71 % to 100 % of total nitrification. However, when ammonia nitrogen was present in the system, autotrophic nitrification became the main mechanism, and the contribution of fungal nitrification to total nitrification was only 15.96 %. Additionally, fungi were capable of directly utilizing nitrite for nitrate production with a rate of 4.65 mg L−1 d−1. This research article contributes to the understanding of the importance of fungi in the aerated landfill systems, filling a gap in knowledge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acid hydrothermal solution was recycled to prepare biomass-derived hydrochar. • Hydrothermal solution recycling enhanced hydrothermal humification of hydrochar. • The hydrothermal humic acid yield of 71.2 wt% from hydrochar was achieved. • Polymerized chemicals in hydrochar could humify to fulvic-like substances. Acid hydrothermal treatment of biowaste is a beneficial approach for producing hydrochar with high hydrothermal humic acid (HHA) selectivity, along with a by-product hydrothermal solution containing saccharides, furans, and aromatic compounds. Conversely, alkaline hydrothermal conditions are suitable for humification to form HHA. This study explored the recycling of hydrothermal solution as a solvent for hydrochar production, aiming to reduce salt content in wastewater and the need for acid/alkali inputs. The acidity of the recycled hydrothermal solution significantly influenced the quality of the prepared hydrochar in terms of alkaline hydrothermal humification. Insufficient solution acidity resulted in a decrease in hydrochar-derived HHA yield (65.0 wt% to 20.2 wt%). Maintaining sufficient acidity (pH 0) in the recycled hydrothermal solution not only improved the hydrochar yield (29.6 wt% to 33.1 wt%) via polymerization or condensation reactions but also maintained ab high level of hydrochar-derived HHA yield (68.2 wt% to 71.2 wt%). This can be attributed to adequate hydrolysis of biowaste and polymerization of soluble chemicals into the hydrochar. Furthermore, the total yields of hydrochar-derived and solution-derived humic substances were higher compared to values obtained without hydrothermal solution recycling. This study presents an innovative hydrothermal process for HHA production, offering cost savings and environmental benefits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen addition could significantly improve the hydrothermal humic acid yield. • Oxygen addition could reduce the energy input required for hydrothermal humification. • Excessive oxygen can cause the degradation of humic acid. • Hydrothermal humic acid with oxygen treatment showed high potential in practical applications. The utilization of biomass as a raw material and production of hydrothermal humic acid (HHA) through hydrothermal method using hydrochar as an intermediate product is a sustainable approach for the preparation of humic acid. In this study, hydrochar was prepared through acid hydrothermal treatment of corn straw and then oxygen was introduced to alkaline hydrothermal treatment of hydrochar to improve the yield of humic acid. It was discovered that an oxygen pressure of 5 bar could significantly enhance the yield of HHA from 41.9 wt% to 49.2 wt% at a hydrothermal temperature of 180 °C, while oxygen pressures of 10 bar and 20 bar led to a decrease in HHA yield (41.5 wt% to 28.2 wt%). Oxygen addition could also reduce the energy input and the economic cost required for hydrothermal reactions. Further study revealed that the increase in HHA yield was the oxidation of aliphatic carbon in the solid residue derived from hydrochar by oxygen, which became part of the HHA and resulted in weaker fluorescence intensity of the HHA. However, excessive oxygen could increase the oxygen-containing functional groups of the HHA while also causing further cleavage of macromolecular components with high carbon numbers, generating smaller molecules that partially dissolve in the liquid phase. The HHA synthesized at an oxygen pressure of 5 bar showed good performance in promoting Chinese cabbage seedlings growth and was superior to the HHA synthesized in the absence of oxygen in terms of cadmium adsorption. This study proved an improved hydrothermal humification method and provided technical support for industrial applications. [ABSTRACT FROM AUTHOR]

Microwave hydrothermal liquefaction (MHTL) was introduced to transform watermelon peel to 5-hydroxymethylfurfural (HMF), a top value added chemical from biomass. The key MHTL process parameters of holding temperature, holding time, and liquid-to-solid ratio were optimized by a Box-Behnken design and response surface methodology. The highest HMF yield (3.8%) was obtained with a holding temperature of 135 °C, holding time of 6 min, and liquid-to-solid ratio of 12:1, respectively. The economic evaluation showed that 1.52 kg of HMF could be obtained from 1 t of fresh watermelon peel under the optimum MHTL conditions. It indicates a feasible and environmental friendly waste valorization method. • Watermelon peel was first applied to the production of HMF by using MHTL. • A highest HMF yield of 3.8% under the optimal MHTL conditions was observed. • Economic value of HMF obtained from fresh watermelon peel exceeds 1520$/t. • Compared with other processes, the MHTL is more energy saving. [ABSTRACT FROM AUTHOR]

Abstract Green waste (GW), rich in cellulose and hemicellulose, is a valuable resource. Developing alternative sustainable technologies to utilize GW is attracting increasing attention. In this study, microwave hydrothermal carbonization (MHTC) process parameters including holding temperature, holding time, and liquid-to-solid ratio were optimized by a response surface design to tailor the properties of hydrochar. The hydrochar characteristic was mainly evaluated by the calorific value. The results showed that the highest hydrochar calorific value (∼23.01 MJ kg−1) could be observed at a holding temperature of 190 °C, a holding time of 1 h and liquid-to-solid ratio of 8:1. Correspondingly, the hydrochar yield ranged from 50.40% to 76.80%. The economic evaluation of hydrochar was also done in this work. These results show that the GW-derived hydrochar warrants further investigations as a fuel source and as an adsorbent material. Graphical abstract Image 1 Highlights • Green waste was mainly transformed to hydrochar by microwave hydrothermal technology. • Hydrochar is a good fuel with high calorific value and considerable yield. • Microwave hydrothermal carbonization conditions were optimized. [ABSTRACT FROM AUTHOR]

[Display omitted] • The humification behavior of lignocellulosic components was investigated. • Lignin with its rich aromatic structures had the highest humic acid contribution. • Interactions of lignocellulosic components improved the humic acid production. • Three possible pathways for hydrothermal humic acid formation were suggested. The humification behavior of lignocellulosic components (i.e. , cellulose, hemicellulose and lignin) under acid-alkali two-step hydrothermal treatment was investigated with particular interest of revealing the contribution of single components as well as their interaction to hydrothermal humic acid (HHA). Lignin with its rich aromatic structures, had the highest HHA contribution (51.8 ± 1.0 wt%), while cellulose and hemicellulose only contributed 8.8 ± 1.6 wt% and 20.1 ± 4.4 wt% HHA yields, respectively. The conversion pathway of these components toward humification indicated that the hydrochar (HC) rather than the hydrothermal solution (HS) had higher humification capability under alkaline hydrothermal conditions because the hydrochar-derived HHA yields of 40.8 ± 2.0 wt% (cellulose), 66.2 ± 6.4 wt% (hemicellulose) and 55.4 ± 6.1 wt% (lignin) were achieved. In addition, co-hydrothermal treatment of cellulose, hemicellulose and lignin under this process improved the HHA production ascribing to the increased HC yield (23.1–53.1 %). The chemical characteristics of HHA products from lignocellulosic components (cellulose, hemicellulose, lignin) and their combinations were similar to the acknowledged natural humic acids. The hydrothermal humification of biowaste mainly passes through a top-down pathway (i.e. , HHA forms from the oxidation of large fragments of hydrochar) as well as two bottom-up pathways (i.e. , the soluble chemicals conduct the polymerization reaction for HHA production and react with the fragments from HC to synthesize the HHA). This study filled the lack of knowledge in the field of biowaste humification. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coal-like hydrochar had great potential for humic acid production, up to 65 wt%. • The contribution of each component in hydrochar to humic acid was revealed. • Humic substances enhanced hydrothermal humification of hydrochar residue. • Humins formed in acid hydrothermal condition had high humic acid selectivity. • Four pathways of alkaline hydrothermal humification of hydrochar were confirmed. Acid hydrothermal treatment of biowaste is favorable for producing hydrochar and corresponding hydrothermal solution containing saccharides, furans and aromatic compounds, while the alkaline hydrothermal condition is beneficial for their humification to form hydrothermal humic acid (HHA). Herein, the humification potential of hydrochar, hydrothermal solution, and their mixture under alkaline hydrothermal conditions was compared to further reveal their contribution to HHA. The result showed the main source of HHA was hydrochar, occupying 70 wt% of total HHA yield from their mixture while hydrothermal solution only contributed 17 wt%. Moreover, the HHA that existed in hydrochar (denoted as HHA acid) was 32 wt% while the hydrochar-derived HHA obtained after alkaline hydrothermal treatment (denoted as HHA alk) increased to 65 wt%, close to that from commercial coal or lignite. The hydrochar was further separated into four components, i.e. hydrothermal fulvic acid (HFA), stable HHA acid (S-HHA acid) non-stable HHA acid (N -HHA acid) and remaining substance (RS), aiming to reveal the major pathway of the incremental HHA production under alkaline hydrothermal condition. Reactions of RS + HFA, RS + N -HHA acid and self-synthesizing of RS all contributed to the incremental HHA alk yield with the major contribution (75C%) from the first combination (RS + HFA). The pathways of alkaline hydrothermal humification of hydrochar were revealed after analyzing the molecular level structure of HHA alk by UPLC-MS. This in-depth analysis fills the knowledge gap in the mechanism of hydrothermal humification of biowaste. [ABSTRACT FROM AUTHOR]

Humic substance is vital for soil fertility and has wide applications such as soil remediation agents, organic fertilizer and adsorbents. The results of pH effect on artificial humic acids (AHAs) production demonstrated that acid hydrothermal conditions are favorable for biomass waste dissolution and formation of AHA precursors such as saccharides, furans, organic acids and phenols; whereas alkaline hydrothermal conditions are suitable for AHAs production from these precursors. Enhanced humification from biomass waste with a combined acid - alkaline hydrothermal process was proposed. The solid product known as hydrochar was reduced to only 5 wt% after this process indicating the significant improvement of dissolution and transformation. The AHAs concentration of 28.28 ± 0.98 wt% obtained from corn stalk was the highest yield so far, 10 times higher than ever reported. The carbon flow analysis indicated that the selectivity of AHA-C was 43.2% of the initial carbon in corn stalk. Our study provides a new way of mass production of AHAs in short period, which has great potential for industry application. • Two stages hydrothermal process shows great potential in humic acid production. • Highest humic acid yield of 28.74 wt% was achieved with corn stalk. • The solid residue was notably reduced to only 5 wt% after the hydrothermal process. • Acidic hydrothermal pretreatment promotes humic acid precursors formation. [ABSTRACT FROM AUTHOR]

5-Hydroxymethylfurfural (HMF) and levulinic acid (LA) are regarded as value-added platform chemicals that can be derived from biomass waste. However, humins are inevitably produced during valorization processes, reducing the product yields. Previous studies indicated that microwave heating combined with acidic seawater as a reaction medium promotes HMF formation. The present work therefore investigated the relationship between the production of HMF and LA in the liquid phase and that of insoluble humins (that is, hydrochar) under microwave heating in acidic seawater. The selectivities for HMF and LA were found to decrease as the reaction time was increased, as a result of hydrochar formation, and both dehydration and decarboxylation evidently dominated the production of hydrochar in succession. HMF evidently played the most important role in hydrochar formation, and was consumed approximately seven times more rapidly than either fructose or LA. The hydrochar formation mechanism reported herein may be applicable to other similar hydrothermal processes. Unlabelled Image • Hydrochar formation has two steps via dehydration and decarboxylation. • The chemical equation of fructose, HMF, LA and hydrochar was built. • HMF consumption is 7 times than that of fructose and LA for hydrochar synthesis. • The structure of initial hydrochar involving fructose and HMF was inferred. [ABSTRACT FROM AUTHOR]

5-Hydroxymethylfurfural (HMF) as value-added platform chemical can be derived from biomass. This study used microwave hydrothermal liquefaction (MHTL) to obtain HMF from sugarcane bagasse in acidic seawater conditions. The key processing parameters including temperature, reaction time, and liquid-to-solid ratio (L/S) were evaluated and optimized. The highest HMF yield of 8.1 wt% was obtained at 149 °C with a reaction time of 4 min and a L/S value of 12:1, respectively. This yield is considerable and even higher than the yield derived from sugarcane molasses under similar microwave conditions in the absence of seawater. Hence, acidic seawater was found to promote the hydrolysis of sugarcane bagasse to give HMF precursor (i.e. fructose and glucose), while simultaneously inhibiting the conversion of HMF to levulinic acid under MHTL conditions, possibly explaining the high HMF yield. This method presents a new and sustainable means of transforming waste biomass to valuable substances using seawater or brine wastewater. •A highest HMF yield of 8.1 wt% under optimal MHTL condition was observed. • Acidic seawater can effectively improve the conversion of bagasse into HMF. • Seawater promote the bagasse conversion and inhibit the production of levulinic acid. • HMF degradation rate in hydrochloric acid is 4 times than that of in acidic seawater. [ABSTRACT FROM AUTHOR]

• MHTC could effectively improve the dehydration reaction comparing with the HTC. • MHTC could enhance the energy properties of hydrochar more effectively. • MHTC increased the hydrochar specific surface areas than HTC at 190 °C. • MHTC process has advantage of lower energy consumption. Green waste (GW), a typical biomass waste, was used to produce hydrochar using microwave hydrothermal carbonization (MHTC). The results indicate that MHTC promotes the dehydration of GW to a greater extent than traditional oven or oil bath heating under the same hydrothermal conditions. The hydrochar obtained from the MHTC process showed an energy densification factor of 1.27 and a fuel ratio of 0.19, both of which exceeded those produced by traditional hydrothermal processes. Thermogravimetric data also demonstrated that hydrochar obtained using MHTC had better incineration properties. Moreover, the material possessed a high specific surface area and a more porous structure, resulting in improved adsorption properties. The result of value and potential evaluation demonstrated that the MHTC process also displays the lower energy consumption of operation. Hydrochar generated from GW is a potential environmentally friendly functional material, and MHTC appears to be a suitable means of producing this substance. [ABSTRACT FROM AUTHOR]

The present study describes the conversion of zinc into a sulfide-containing plating sludge via a microwave hydrothermal sulfidation (MHS) process for use in heavy metal remediation by flotation. The research herein focused on circumventing the operational issues of traditional hydrothermal sulfidation (THS) at high temperature and high pressure. The following optimized process conditions of temperature 153°C, reaction time 63 min, liquid-to-solid ratio 16:1 and S2− concentration 49% were obtained using a single-factor test and the Box–Behnken design test, to yield a maximum sulfidation ratio of 92.90%. Moreover, the economic analysis shows the superiority of the MHS process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pt@C significantly improve the electron transfer efficiency and caproate production. • Pt@C increase the relative abundance of chain elongators (Clostridium kluyveri) • Pt@C promote microbial metabolic activity and enzyme expression. Carboxylate chain elongation can create value-added bioproducts from the organic waste. The effects of Pt@C on chain elongation and associated mechanisms were investigated in simulated sequencing batch reactors. 5.0 g/L of Pt@C greatly increased the synthesis of caproate, with an average yield of 21.5 g COD/L, which was 207.4% higher than the trial without Pt@C. Integrated metagenomic and metaproteomic analyses were used to reveal the mechanism of Pt@C-enhanced chain elongation. Pt@C enriched chain elongators by increasing the relative abundance of dominant species by 115.5%. The expression of functional genes related to chain elongation was promoted in the Pt@C trial. This study also demonstrates that Pt@C may promote overall chain elongation metabolism by enhancing CO 2 uptake of Clostridium kluyveri. The study provides insights into the fundamental mechanisms of how chain elongation can perform CO 2 metabolism and how it can be enhanced by Pt@C to upgrade bioproducts from organic waste streams. [ABSTRACT FROM AUTHOR]

[Display omitted] • MHT is an environmentally-friendly food waste valorizing method. • The highest HMF yield from food waste could amount to 4.61 wt%. • Resource productivity for food waste valorization by MHT was the highest. 5-Hydroxymethylfurfural (HMF) is a platform compound with a high added value derived from biomass. In this study, microwave hydrothermal treatment (MHT) was used to produce HMF from food waste (FW). By optimizing the holding temperature (230 °C) and the holding time (15 min), an HMF yield of 4.61 wt% was obtained, the highest value yet achieved. The main HMF precursors exhibited different phenomena: the fructose content decreased as the holding temperature and holding time increased, while the glucose content first increased then decreased. It was proved that the potential profit of HMF production from FW by MHT was 10,674 USD/tonne, and the resource productivity was 60 to 1000 times that of other valorization methods. MHT is a feasible strategy for valorizing FW by producing the high added value product, HMF. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biomass waste-derived biochar with a novel nanoflake self-assembly is presented. • Both heavy metals and organic pollutants can be treated efficiently by the biochar. • A synergistically physical/chemical adsorption behaviors is elucidated. • Biochar has a potential application for treating cross contamination in industry. With the presence of emerging organic pollutants (EOPs) in aqueous systems, the heavy metals (HMs)-transfer mechanism has been given considerable attention again. Here, a facile molten-salt method is used to successfully convert banana waste into nanoflake-assembled biochar (BC350) for the first time. It is a type of macro-mesoporous biochar with a pore size composed of ~ 3.8 nm and ~ 50 nm, and its maximum adsorption capacities are 459 mg g−1 for Pb2+ and 148 mg g−1 for tetracycline (TC), which outperforms the reported adsorbents ranging from several times to dozens of times. The pore-filling effect, electrostatic interaction, coordination affinities and π-π stacking as synergistically physical/chemical adsorption behaviors of BC350 on Pb2+/TC that has been comprehensively elucidated relying on adsorption kinetics and isotherms, and key effect parameter investigation. The competitive adsorption effect becomes insignificantly in the adsorption efficiency of BC350 on Pb2+/TC cross contamination at a control condition. Moreover, BC350 also exhibits outstanding adsorption efficiency (>95%) on Pb2+/TC in five industrial wastewater samples. This study contributes to a plausible mechanism in biochar adsorption removal of metal/organics cross contamination and its potential application explored in industrial wastewater treatment. [ABSTRACT FROM AUTHOR]

Due to increasing industrialization, soils are increasingly contaminated by polycyclic aromatics such as pyrene and need gentle treatment to keep the soil functioning. This study applied a double dielectric barrier discharge (DDBD) plasma reactor and composting reactor to remediate pyrene-contaminated soil. The effect of peak-to-peak applied voltages on the remediation efficiency of pyrene was investigated. The experimental results illustrate that pyrene remediation efficiency increased from 43% to 85% when the peak-to-peak applied voltage was increased from 28.0 to 35.8 kV. When using the combined method of DDBD and composting, 90–99% of pyrene could be removed, while a reduction of 76.5% was achieved using only composting, indicating the superiority of the combined system. Moreover, the authors could demonstrate that DDBD plasma treatment improves humification in the post-composting process as humic acid (HA) concentrations increased to 7.7 mg/g with an applied voltage of 35.8 kV; when composting was used as the sole treatment method, only 3.4 mg/g HA were produced. The microbial activity in the DDBD plasma-treated soil peaked on the 5th day and had a 2nd rise afterwards. The authors demonstrate that the combined technology of DDBD plasma and composting is a promising method for soil remediation with persistent organic pollutants. This treatment approach improves pollutant degradation efficiency and facilitates further humification, potentially restoring the function of contaminated soil. This approach could be considered a cost-effective and green strategy for soil remediation with persistent organic pollutants. [Display omitted] • Bioremediation of Pyrene contaminated soil under influence of NTP. • Composting combined with DDBD plasma pretreatment showed higher pyrene removal efficiency than composting alone. • Higher voltage of DDBD plasma reactor enhanced pyrene remediation. • Combined process was also superior in humification and microbial activity. [ABSTRACT FROM AUTHOR]