Insight into the effective electrocatalytic sulfide removal from aqueous solutions using surface oxidized stainless-steel anode and its desulfurization mechanism.

The electrochemical oxidation of hydrogen sulfide (H2S) has shown its potential for the real application of H2S emission control in wastewater treatment. In this study, a surface corrosion treatment of stainless steel (SS) was optimized by regulate Ni content in the oxide film on the SS AISI 304 surface for sulfide removal. The X-ray photoelectron spectroscopy and linear sweeping voltammetry results indicated a higher Ni content in the oxide film of surface-oxidized stainless steel (SOSS) attributed to a higher sulfide removal potential. Sulfide removal experiment results showed that SS-150 (with 150 s anodic pretreatment) anodes achieved the highest Ni content of 69% with the best sulfide removal efficiency, i.e., 97% within 48 h, which increased by 20% compared to the untreated SS. This study also demonstrated a strategy for in situ removal of deposited sulfur on the anodes by cathodic treatment at -0.38 V vs. RHE to alleviate the common issue of sulfur passivation. Density functional theory (DFT) calculation revealed that NiOOH was the major active species in SS-150 oxide film for a faster sulfide removal rate. The study developed a SS surface modification process for Ni content regulation that contributed to better sulfide removal efficiency.

Synthesis and characterization of TiO2/hydrochar matrix composites for enhanced ammonia degradation.

This study explores the limitations of TiO2 as a photocatalyst, focusing on its narrow bandwidth and high electron-hole complexation probabilities that restrict its applications. A novel one-pot synthesis method for TiO2/hydrochar matrix composites is presented, with variations achieved through control of hydrothermal temperature, time, and loading concentration. The efficacy of these composites in ammonia removal is investigated, revealing optimal performance for the composite denoted as 3Ti-160-7, synthesized with a titanium salt concentration of 0.3 mol L-1, a hydrothermal temperature of 160 °C, and a hydrothermal time of 7 hours. Comparative analyses with commercial TiO2 (P25) and hydrochar demonstrate superior performance of 3Ti-160-7, exhibiting significantly lower ammonia concentration and reduced NO and NO2 concentrations. This research underscores the cost-effectiveness and application potential of TiO2/hydrochar matrix composites, offering valuable insights for the enhancement of photocatalytic activity and broader applicability in addressing TiO2-related challenges.

Nickel-Catalyzed mesoporous biochar for enhanced adsorptive oxidation of aqueous Sulfide: An investigation of influencing factors and mechanisms.

Biochar (BC) is a low-cost and electroactive adsorbent for removing sulfide in aqueous media, which toxifies aquatic organisms and corrodes water treatment facilities. However, it lacks a pore structure for sulfide ion (S2-) mass transfer to active sites. Herein, it is shown that nickel-modified biochar (BC-Ni) adsorbed S2- 2.72-fold faster than BC alone and attained a 1244 ± 252 mg-sulfide/g maximum adsorption capacity due to markedly increased mesopores, while BC attained 583 ± 250 mg-sulfide/g. Factors influencing S2-sorption and theoretical sorption kinetics and isotherms models were evaluated. Structural and surface compositions of BC and BC-Ni were examined using state-of-the-art characterizations. The results suggest that S2- was adsorbed via pore diffusion, pore filling, and cation bridging and oxidized to elemental sulfur and sulfate with quinone and hydrogen peroxide generated from dehydrogenation of hydroquinone on the BC-Ni by metallic nickel in the carbon matrix. This study would spur biomass valorization and desulfurization.

Impacts of molybdate and ferric chloride on biohythane production through two-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue.

Biohythane production through one-stage anaerobic digestion of sulfate-rich hydrolyzed tofu processing residue has been hampered by high H2S production. Herein, two-stage anaerobic digestion was investigated with the addition of molybdate (MoO42-; 0.24-3.63 g/L) and ferric chloride (FeCl3; 0.025-5.4 g/L) to the dark fermentation stage (DF) to improve biohythane production. DF supplemented with 1.21 g/L MoO42- increased hydrogen yield by 14.6% over the control (68.39 ml/g-VSfed), while FeCl3 had no effect. Furthermore, the maximum methane yields of methanogenic fermentation were 524.8 and 521.6 ml/g-VSfed with 3.63 g/L MoO42- and 0.6 g/L FeCl3 compared to 466.07 ml/g-VSfed of the control. The maximum yields of biohythane and energy were 796.7 ml/g-VSfed and 21.8 MJ/kg-VSfed with 0.6 g/L FeCl3 when the sulfate removal efficiency was 66.7%, and H2S content was limited at 0.08%. Therefore, adding 0.6 g/L FeCl3 is the most beneficial in improving energy recovery and sulfate removal with low H2S content.

Endogenous calcium enriched hydrochar catalyst derived from water hyacinth for glucose isomerization.

Water hyacinth is a major aquatic plant in ecological restoration which propagates rapidly, whereas its biomass waste lacks value-added utilization routes. To address this problem, we put forth an innovative two-step carbonization strategy to convert water hyacinth to catalyst for isomerization of glucose to fructose. Through combining the hydrothermal carbonization and pyrolysis, catalyst morphology including its carbon substrate and calcium salts was successfully engineered. The prepared hydrochar-based catalyst presented an outstanding catalytic performance, the optimal of which could obtain 31% fructose yield with 89% selectivity at 120 °C for 45 min in water and maintain the reactivity for at least three runs. The catalytic reactivity was derived from the crystallization of endogenous alkaline earth calcium in water hyacinth, which was comparable to catalysts doped with expensive metals. Besides, the equipment and energy requirements for preparation were quite low-demanding (calcined only at 400 °C for 1 h). This study not only pioneers a sustainable way to upcycle aquatic biomass, but also invents a low-cost and efficient catalyst for biorefinery through the production of engineered carbon.

Combination of ultrasonic and acidic pretreatments for enhancing biohythane production from tofu processing residue via one-stage anaerobic digestion.

Tofu processing residues (TPR) have received more attention as a source of bioenergy. However, their low solubility has hindered biohythane generation. Consequently, the ultrasonic and H2SO4 pretreatments were combined and compared for the first time to improve the hydrolysis of organic matter and carbohydrate and increase free amino nitrogen generation from TPR. Besides, the impact of pretreatments on biohythane generation was investigated. Under the optimal conditions of 7.54% substrate level, 8% H2SO4 concentration, 80 °C and 50 min, the coincident ultrasonic-H2SO4 pretreatment enriched the contents of soluble chemical oxygen demand, reducing sugar, and free amino nitrogen to 49675 mg/L, 26 g/L, and 1721 mg/L, respectively, greater than individual pretreatments. Also, Biohythane yield increased by 4.24-13.61% over control (389.42 ± 23.7 ml/g-VSfed). Furthermore, hydrogen yield at 42.5 ± 2.08 and 28.1 ± 1.07 ml/g-VSfed and sulfate removal efficiency at 93 and 92% were significantly improved with ultrasonic-H2SO4 and H2SO4 pretreatments, respectively, indicating acidogenic and sulfidogenic activity enhancement.

Effects of hydrothermal pretreatment and bamboo hydrochar addition on anaerobic digestion of tofu residue for biogas production.

The effect of hydrothermal pretreatment (HTP) of tofu residue (TR) and co-digestion of TR with hydrochar (HC) and a liquid fraction (LF) of hydrothermal pretreatment on biogas production was studied. The highest biogas and methane yield observed with the pretreated TR at HTP temperature of 140 °C reached 288 and 207 L/Kg VS, 24 and 37% above than the raw TR (control), respectively, and the highest content of methane 72%. Adding 4 g/L of HC (produced at 200 °C) enhanced the methane and biogas yield by 18 and 19% compared to untreated TR, respectively. It was found that HTP at temperature 140 °C and additive HC-200 (4 g/L) was the most efficient for biogas production from tofu residue and significantly reduced the digestion time needed from 20 to 10-13 days to reach 95% of biogas yield, which may result in substantial economic benefits.

Effects of Hydrothermal Pretreatment and Hydrochar Addition on the Performance of Pig Carcass Anaerobic Digestion.

Proper disposal and utilization of dead pig carcasses are problems of public concern. The combination of hydrothermal pretreatment (HTP) and anaerobic digestion is a promising method to treat these wastes, provided that digestion inhibition is reduced. For this reason, the aim of this work was to investigate the optimal HTP temperature (140-180°C) for biogas production during anaerobic digestion of dead pigs in batch systems. In addition, the effects of hydrochar addition (6 g/L) on anaerobic digestion of pork products after HTP in continuous stirred tank reactors (CSTR) were determined. According to the results, 90% of lipids and 10% of proteins present in the pork were decomposed by HTP. In addition, the highest chemical oxygen demand (COD) concentration in liquid products (LP) reached 192.6 g/L, and it was obtained after 170°C HTP. The biogas potential from the solid residue (SR) and LP was up to 478 mL/g-VS and 398 mL/g-COD, respectively. A temperature of 170°C was suitable for pork HTP, which promoted the practical biogas yield because of the synergistic effect between proteins and lipids. Ammonia inhibition was reduced by the addition of hydrochar to the CSTR during co-digestion of SR and LP, maximum ammonia concentration tolerated by methanogens increased from 2.68 to 3.38 g/L. This improved total biogas yield and degradation rate of substrates, reaching values of 28.62 and 36.06%, respectively. The acetate content in volatile fatty acids (VFA) may be used as an index that reflects the degree of methanogenesis of the system. The results of the present work may also provide guidance for the digestion of feedstock with high protein and lipid content.

Glucose isomerization catalyzed by swollen cellulose derived aluminum-hydrochar.

Since efficient isomerization of glucose to fructose is vital for valorizing cellulose fraction of biomass to value-added chemicals, an approach of engineering aluminum-hydrochar catalyst by impregnating aluminum on swollen cellulose derived hydrochar has been studied. The results showed that Al-hydrochar calcinated at 300°C achieved fructose yield of 26.3% in acetone/H2O reaction medium. It was found that the amorphous Al structures with nano-size on the surface of the carbon microspheres were the major contributor of the catalytic activity on glucose to fructose isomerization, while the formation of Al crystal had an inhibition effect on glucose isomerization. The deactivation study of Al-hydrochar catalysts showed the exfoliation of colloidal carbon containing aluminum active catalytic sites. This finding provides a novel strategy for efficient isomerization of glucose by Al-hydrochar prepared through hydrothermal carbonization and mild calcination activation process.

Bamboo derived hydrochar microspheres fabricated by acid-assisted hydrothermal carbonization.

In this study, bamboo residues derived functional hydrochar microspheres have been fabricated by different acids-assisted hydrothermal carbonization including hydrochloric aicd, sulfuric acid or nitric acid.The energy-dispersive X-ray fluorescence spectroscopy and Fourier Transform Infrared spectroscopy analyses showed that sulfur- and nitrogen-containing functional groups were grafted on the surface of hydrochar microspheres, respectively. Elemental analysis indicates that the addition of acids has a significant influence on the hydrothermal reaction pathway and promotes the hydrolysis process. When the hydrothermal carbonization temperature is 220 °C, hydrochloric acid and nitric acid can effectively overcome the agglomeration of hydrochar microspheres and form single micron carbon sphere. Irregularly shaped hydrochar particles groups were formed during sulfuric acid-assisted hydrothermal treatment. The results indicate the viability of acid assisted hydrothermal carbonization to produce the functional hydrochar microsphere using bamboo residues.

Green synthesis of aluminum-hydrochar for the selective isomerization of glucose to fructose.

Hydrochar microspheres supported Al catalysts with hierarchically porous structure (Al/HPHMs) for glucose to fructose isomerization were fabricated. Superior catalytic selectivity (93.3%) and fructose yield (32.6%) were achieved in aqueous under 160 °C for 20 min. Hierarchically porous structure was formed after KHCO3 and K2CO3 activation and the roles of KHCO3 and K2CO3 in controlling the Al phase and tailoring morphology of hydrochar supported Al were evaluated. The major active sites were characterized as Al hydroxides including ß-Al(OH)3, γ-Al(OH)3, γ-AlO(OH), Al-C-O linkages. Active sites by KHCO3 activation with high contents of Al-C-O and Al(OH)3 have better selectivity. Oxygen-containing functional groups including aluminum­oxygen groups on the hydrochar microspheres have contributed to the formation of hydrogen bond and π-π interactions between glucose and Al species. Green process synthesized aluminum-hydrochars have potential for their application as a variety of stable, recyclable, and efficient catalysts for lignocellulosic biorefining.

Quantitative visualization of subcellular lignocellulose revealing the mechanism of alkali pretreatment to promote methane production of rice straw.

BACKGROUND: As a renewable carbon source, biomass energy not only helps in resolving the management problems of lignocellulosic wastes, but also helps to alleviate the global climate change by controlling environmental pollution raised by their generation on a large scale. However, the bottleneck problem of extensive production of biofuels lies in the filamentous crystal structure of cellulose and the embedded connection with lignin in biomass that leads to poor accessibility, weak degradation and digestion by microorganisms. Some pretreatment methods have shown significant improvement of methane yield and production rate, but the promotion mechanism has not been thoroughly studied. Revealing the temporal and spatial effects of pretreatment on lignocellulose will greatly help deepen our understanding of the optimization mechanism of pretreatment, and promote efficient utilization of lignocellulosic biomass. Here, we propose an approach for qualitative, quantitative, and location analysis of subcellular lignocellulosic changes induced by alkali treatment based on label-free Raman microspectroscopy combined with chemometrics. RESULTS: Firstly, the variations of rice straw induced by alkali treatment were characterized by the Raman spectra, and the Raman fingerprint characteristics for classification of rice straw were captured. Then, a label-free Raman chemical imaging strategy was executed to obtain subcellular distribution of the lignocellulose, in the strategy a serious interference of plant tissues' fluorescence background was effectively removed. Finally, the effects of alkali pretreatment on the subcellular spatial distribution of lignocellulose in different types of cells were discovered. CONCLUSIONS: The results demonstrated the mechanism of alkali treatment that promotes methane production in rice straw through anaerobic digestion by means of a systemic study of the evidence from the macroscopic measurement and Raman microscopic quantitative and localization two-angle views. Raman chemical imaging combined with chemometrics could nondestructively realize qualitative, quantitative, and location analysis of the lignocellulose of rice straw at a subcellular level in a label-free way, which was beneficial to optimize pretreatment for the improvement of biomass conversion efficiency and promote extensive utilization of biofuel.

Anaerobic co-digestion of fish processing waste with a liquid fraction of hydrothermal carbonization of bamboo residue.

The effect of different mixing ratios of fish processing waste (FPW) with a liquid fraction (LF) of hydrothermal carbonization (HTC) of bamboo residues on biogas and methane yield was investigated. The different mixing ratios (FPW + LF) and HTC temperature (200-280 °C) had significant effects on biogas and methane production. The anaerobic co-digestion of the various mixing ratio of FPW and LF of bamboo residues did not enhance the methane yield compared to the AD of FPW alone. However, a mixture of 75FPW + 25LF(2 2 0) presented a comparable methane production (133 mL/g VS) to that achieved with 100FPW (142 mL/g VS), which represents an increase of only 6.4%. The ratio of 75FPW + 25LF(2 2 0) increased the biogas yield by 81% compared to the control group of 100LF(2 2 0). The mixing ratio of 75 FPW + 25LF(2 2 0) did not require clean water input to dilute FPW for biogas production and can be a practical waste management method.

Corn stover valorization by one-step formic acid fractionation and formylation for 5-hydroxymethylfurfural and high guaiacyl lignin production.

One-step fractionation with concentrated formic acid at elevated temperatures with short retention time was investigated for corn stover valorization. Crude pulp (CP) with high purity of cellulose and FA-lignin (FAL) with high guaiacyl content were fractionated through one-step mild pretreatment. Formylation reaction on both CP and FAL fractions occurred during the pretreatment and improved the hydrophobicity and thermal stability of CPs and FALs. The presence of formyl group on CPs significantly inhibited the enzymatic hydrolysis efficiency for sugar production, however, the formylated cellulose showed super high reactivity and selectivity for HMF production through catalysis by maleic acid and aluminum chloride in acetonitrile-water co-solvent system. In addition, the fractionated FAL fraction exhibited a loose structure which is prominent for its further catalytic conversion into chemicals and energy.

Effect of bamboo hydrochar on anaerobic digestion of fish processing waste for biogas production.

The effect of hydrothermal carbonization (HTC) temperature and bamboo hydrochar (BHC) addition on biogas production in anaerobic digestion of fish processing waste (FPW) was studied. HTC temperature (200-280 °C) had significant effects on methane yield and content, but the BHC had little effects. The maximum biogas yield observed with HTC at 200 °C and a BHC adding ratio of 1:2 (dry mass ratio of FPW to BHC) reached 292 L/kg volatile solids (VS), which were 64% higher than the control group with only FPW, with the maximum methane yield of 219 L/kg-VS and highest net methane energy yield of 3410 kJ/kg-VS. The obtained results can be used to design an efficient anaerobic digestion process for treating and effectively utilizing fish processing waste.

Evaluation of engineered hydrochar from KMnO4 treated bamboo residues: Physicochemical properties, hygroscopic dynamics, and morphology.

In this study, a novel approach was developed to prepare engineered hydrochar from KMnO4 treated bamboo residues through hydrothermal carbonization. The hydrochar yields were within a specified range of 61.8-67.8% at 180 °C and 39.8-45.0% at 260 °C, respectively. The higher temperature led to the higher C content, lower H/C and O/C ratio, whereas the ash content increased with increasing KMnO4 concentration, causing the increase of solid yield as well as the decrease of C content. Pseudo-second kinetic model was optimal to describe bamboo hydrochar's hygroscopic dynamic, and the engineered hydrochar produced at 260 °C and 1.0 wt% concentration obtained the better hydrophobicity of 0.82%. SEM-EDS and XRD analysis confirmed the existence of manganese carbonate on the surface of engineered hydrochar, from which we inferred the chemical complexation between KMnO4 and hydrochar.

Nondestructive and rapid determination of lignocellulose components of biofuel pellet using online hyperspectral imaging system.

BACKGROUND: In the pursuit of sources of energy, biofuel pellet is emerging as a promising resource because of its easy storage and transport, and lower pollution to the environment. The composition of biomass has important implication for energy conversion processing strategies. Current standard chemical methods for biomass composition are laborious, time-consuming, and unsuitable for high-throughput analysis. Therefore, a reliable and efficient method is needed for determining lignocellulose composition in biomass and so to accelerate biomass utilization. Here, near-infrared hyperspectral imaging (900-1700 nm) together with chemometrics was used to determine the lignocellulose components in different types of biofuel pellets. Partial least-squares regression and principal component multiple linear regression models based on whole wavelengths and optimal wavelengths were employed and compared for predicting lignocellulose composition. RESULTS: Out of 216 wavelengths, 20, 10 and 17 were selected by the successive projections algorithm for cellulose, hemicellulose and lignin, respectively. Three simple and satisfactory prediction models were constructed, with coefficients of determination of 0.92, 0.84 and 0.71 for cellulose, hemicellulose and lignin, respectively. The relative parameter distributions were quantitatively visualized through prediction maps by transferring the optimal models to all pixels on the hyperspectral image. CONCLUSIONS: Hence, the overall results indicated that hyperspectral imaging combined with chemometrics offers a non-destructive and low-cost method for determining biomass lignocellulose components, which would help in developing a simple multispectral imaging instrument for biofuel pellets online measurement and improving the production management.

Effect of hydrothermal and Ca(OH)2 pretreatments on anaerobic digestion of sugarcane bagasse for biogas production.

The effect of hydrothermal (HTP) and Ca(OH)2 pretreatments on the biogas produced by the anaerobic digestion of sugarcane bagasse (SCB) was studied. HTP, Ca(OH)2 and combination pretreatment had significant effects on hemicellulose and lignin degradation during pretreatment and methane yield through digestion. The highest biogas production observed in combination pretreatment HTP 180 + 8.5% of SCB reached 318 mL/g Volatile Solids (VS), which were 47% higher than the untreated SCB, with the highest methane content 69% and highest lignin degradation 44%. The functional groups and the structural changes in the pretreated SCB have also been analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) analysis. Kinetic analysis of methane production potential from SCB was determined to compare ultimate methane yields and kinetic constants. The results of this research contribute useful information to improve the efficiency of anaerobic digestion of SCB by pretreatment.

Effect of hydrochar on anaerobic digestion of dead pig carcass after hydrothermal pretreatment.

Incineration and burial are the current practices for pig carcasses disposal but are not environmentally friendly. Anaerobic digestion can be a better alternative if the process inhibition by carcass digestion can be ameliorated. This study successfully mitigated the inhibition in anaerobic digestion of carcasses by hydrochar addition and by co-digestion with RS and HRS. Biogas production from SP of the pretreated hydrothermal carcasses was enhanced by 60.7 to 90.8% through hydrochar addition. The highest biogas production of 450 mL/g-VS was obtained at 4 g-hydrochar/L addition. The methane content was also increased from 57.5% to up to 69.8%. Each gram of hydrochar removed 25 mg of ammonium and 50 mg of VFA. Hydrochar addition promoted the conversion of VFA to biogas by strengthening the intensity of functional groups and the immobilization of microbial biomass. Co-digestion of SP with RS or HRS also increased the biogas production, and the optimal production of 428 mL/g VS was obtained at 70% SP and 30% RS. The co-digestion of carcass SP with RS and the addition of hydrochar can be a promising solution for improving biogas production from a pig carcass, and can be potentially developed as a sustainable waste management method.

Effects of inoculum to substrate ratio and co-digestion with bagasse on biogas production of fish waste.

To overcome the biogas inhibition in anaerobic digestion of fish waste (FW), effects of inoculum to substrate ratio (I/S, based on VS) and co-digestion with bagasse on biogas production of FW were studied in batch reactors. I/S value was from 0.95 to 2.55, bagasse content in co-digestion (based on VS) was 25%, 50% and 75%. The highest biogas yield (433.4 mL/gVS) with 73.34% methane content was obtained at an I/S value of 2.19 in mono-digestion of FW; the biogas production was inhibited and the methane content was below 70% when I/S was below 1.5. Co-digestion of FW and bagasse could improve the stability and biogas potential, also reducing the time required to obtain 70% of the total biogas production, although the total biogas yield and methane content decreased with the increase in bagasse content in co-digestion. Biogas yield of 409.5 mL/gVS was obtained in co-digestion of 75% FW and 25% bagasse; simultaneously 78.46% of the total biogas production was achieved after 10 days of digestion.