Influence of biochar on the removal of Microcystin-LR and Saxitoxin from aqueous solutions.

The present study assessed the effective use of biochar for the adsorption of two potent HAB toxins namely, Microcystin-LR (MCLR) and Saxitoxin (STX) through a combination of dosage, kinetic, equilibrium, initial pH, and competitive adsorption experiments. The adsorption results suggest that biochar has excellent capabilities for removing MCLR and STX, with STX reporting higher adsorption capacities (622.53-3507.46 µg/g). STX removal required a minimal dosage of 0.02 g/L, while MCLR removal needed 0.4 g/L for > 90%. Similarly, a shorter contact time was required for STX removal compared to MCLR for > 90% of toxin removed from water. Initial pH study revealed that for MCLR acidic conditions favored higher uptake while STX favored basic conditions. Kinetic studies revealed that the Elovich model to be most suitable for both toxins, while STX also showed suitable fittings for Pseudo-First Order and Pseudo-Second Order in individual toxin systems. Similarly, for the Elovich model the most suited kinetic model for both toxins in presence of each other. Isotherm studies confirmed the Langmuir-Freundlich model as the best fit for both toxins. These results suggest adsorption mechanisms including pore filling, hydrogen bonding, π-π interactions, hydrophobic interactions, electrostatic attraction, and dispersive interactions.

Assessing hydrothermal carbonization as sustainable home sewage management for rural counties: A case study from Appalachian Ohio.

Improper management of home sewage treatment systems (HSTS) presents major challenges in the developing world, and even in many parts of developed countries, which contribute to health, environmental, economic, and social problems. Hydrothermal treatment, a thermochemical conversion process that is particularly useful for wet wastes, can produce fertilizers from septic tank wastes while eliminating human pathogens. However, hydrothermal treatment requires high temperature and high pressure, which might need additional economical justification when targeted for rural communities. The aim of this study was to investigate the economic feasibility of a hydrothermal treatment facility that can treat septic waste generated in Athens County, Ohio, a rural Appalachian county in the U.S., where failing HSTS have been observed quite frequently. Two different cases were considered for economic analysis, where Case I assumed a decentralized facility and Case II assumed a centralized facility. Results showed that both cases are economically feasible, where Case I and II reached breakeven in years 4 and 6, respectively. Additionally, despite the greater capital investment requirement for Case I, there was also a greater return on investment (ROI) of 2.85 compared to 1.52 for Case II. A sensitivity analysis was examined to determine the effect of solid content in either the septic tank or the reactor's feed, selling price of the fertilizer, and septage pumping costs on the project feasibility. The sensitivity analysis showed that pumping cost is the most significant factor affecting the project feasibility, while the ROI varied about ±80% and ± 200% for Case I and II, respectively, due to only about ±18% change in pumping cost.

Liquid-Liquid Extraction of Furfural from Water by Hydrophobic Deep Eutectic Solvents: Improvement of Density Function Theory Modeling with Experimental Validations.

This study outlines the methodology to model hydrophobic deep eutectic solvent (HDES) interactions to obtain computational results that accurately represent experimental results of furfural removal from water. Computational prediction with high accuracy of HDES behavior could elucidate hydrogen bond interaction in HDES. COSMOtherm modeling and experimental evaluation demonstrated that both decanoic and dodecanoic acid-based HDES can remove furfural from water even at very low concentrations of 0.1 mol %. The modeling methodology considered salts as independent cations, which were paired with the hydrogen bond donor (HBD) species. These resulted in computational predictions of liquid-liquid equilibrium (LLE) between tetra n-alkyl ammonium bromide salt-based HDES with >95% accuracy of experimental results. The COSMOtherm modeling methodology strengthens the understanding of HDES by considering intermolecular forces that affect electron density (σ) of the HDES components to determine the LLE of the HDES-aqueous system. This results in a deep eutectic phase that has a positive sigma potential (potentials, µ(σ), up to 0.1 kcal/mol Å2) at charge densities associated with hydrogen bonding (±0.0084 e/Å2). Though n-alkyl ammonium salts ranging from tetramethyl- to tetraoctylammonium bromide were considered in the computational model, only pentyl- and longer alkyl chains displayed hydrophobic behavior with less than 1% salt loss to the aqueous phase. However, there was still significant water uptake in the eutectic phase (final phase composition containing greater than 60 mol and 12% by mass) for the hydrophobic DES.

Recovery of Macro and Micro-Nutrients by Hydrothermal Carbonization of Septage.

In this study, septic tank waste (i.e., septage) was hydrothermally carbonized (HTC) in order to recover macro and micronutrients, while tracking the fate of residual heavy metals. Three different HTC temperatures (i.e., 180, 220, and 260 °C) at autogenous pressures and two reaction times (i.e., 30 and 120 min) were applied on both solid and liquid septages. Hydrochar and HTC process liquids were characterized using ICP, CHNS, and UV-vis spectroscopy. Treatment at 260 °C for 120 min maximized ammonia recovery, producing a liquid with 1400 mg/L of ammonia. Overall, about 70% of available nitrogen ended up in the liquid phase as nitrate or ammonia. Solid hydrochars show potential for fertilizer use, with high phosphorus content of 100-130 kg/tonne. It was found that heavy metals mainly remained in the solid phase, although the concentrations of heavy metals are mostly lower than U.S. EPA regulation for biosolids with the exception of selenium.

Hydrothermal Liquefaction of Loblolly Pine: Effects of Various Wastes on Produced Biocrude.

In this study, feedstock interaction of cow manure and digested sewage sludge on hydrothermal liquefaction (HTL) of loblolly pine (LP) was evaluated. Noncatalytic HTL experiments were performed at reaction temperatures of 250, 275, and 300 °C at a constant reaction time of 30 min. Cyclohexane and acetone were used for biocrude extraction separately. The study focuses on the characteristics of the produced biocrude, and thus, physicochemical properties of biocrudes were examined by gas chromatography-mass spectrometry, Fourier-transform infrared spectroscopy, density, and viscosity measurements, in addition to comparing mass and energy yields. On a LP basis, the biocrude yield reached as high as 30 and 17% for acetone and cyclohexane extraction, respectively, at the highest reaction temperature. Elemental carbon and energy contents increased with increasing HTL temperature for all cases. Alkalinity of the HTL process liquid (aqueous phase) increases from the HTL of sludge, and thus, it favored the formation of nonpolar compounds in biocrude. On the other hand, acidity of the reaction medium increases with the HTL of manure and pine, and thus, phenolic compounds in biocrude were increasing. Cyclohexane was more effective for sludge/LP biocrude extraction, whereas acetone was effective for manure/LP. Density of cyclohexane extracted sludge/LP biocrudes at 300 °C was less than 1000 kg m-3, whereas acetone-extracted biocrudes had densities greater than 1000 kg m-3. For all the biocrudes, viscosity was reduced considerably for the mixtures when compared to biocrudes from LP alone.

Pyrolysis of hydrochar from digestate: Effect of hydrothermal carbonization and pyrolysis temperatures on pyrochar formation.

Digestate from anaerobic digestion of biomass often contains more than 90% of water, which is economically unfavorable for pyrolysis. Hydrothermal carbonization (HTC) has potential to treat very wet biomass, however, the hydrochar may be acidic, contains polycyclic aromatic hydrocarbons (PAH) and toxic organic substances (e.g., phenolic compounds), and has very low Brunauer-Emmett-Teller (BET) surface area. In this study, pyrolysis of digestate derived hydrochar is performed at various pyrolysis and HTC temperatures. Solid chars were characterized for elemental analysis, pH, PAH, BET, pore size and volume, and phenolic substances, while HTC process liquids were characterized for pH, organic acids, furfural derivatives, and phenolic substances. Physicochemical characteristics of pyro-HTC char were compared with corresponding pyrochar and hydrochar. Pyro-HTC chars produced at higher HTC (i.e., 260°C) and pyrolysis temperatures (i.e., 800°C) showed highest BET surface area (63.5m(2)g(-1)), no PAH, relatively mild basic pH (9.34), and no phenolic compounds.

Characterization of products from hydrothermal carbonization of orange pomace including anaerobic digestibility of process liquor.

In this study, the effect of the temperature and reaction time on hydrothermal carbonization (HTC) of orange pomace was investigated. In addition, a set of anaerobic batch tests were performed to determine the resulting biogas and methane potential of the spent liquor. Hydrochar yields followed a decreasing trend with the increasing temperature, whereas reaction time had no considerably effect on the yield. The evolution of the H/C and O/C atomic ratios from the raw material to the hydrochars suggested that dehydration reactions prevail during HTC. The hydrochars tended to become enriched in Ca, Mg and P minerals by increasing HTC temperature. The heavy metal contents in hydrochars were found below limits and no PAH compound was detected. Anaerobic digestion tests showed that the aqueous phase from HTC can be used as feedstocks for biogas production.

Production, characterization, and biogas application of magnetic hydrochar from cellulose.

Hydrothermal carbonization (HTC) produces carbon-rich nano-micro size particles. In this study, magnetic hydrochar (MHC) was prepared from model compound cellulose by simply adding ferrites during HTC. The effects of ferrites on HTC were evaluated by characterizing solid MHC and corresponding process liquid. Additionally, magnetic stability of MHC was tested by magnetic susceptibility method. Finally, MHC was used as support media for anaerobic films in anaerobic digestion (AD). Ash-free mass yield was around 50% less in MHC than hydrochar produced without ferrites at any certain HTC reaction condition, where organic part of MHC is mainly carbon. In fact, amorphous hydrochar was growing on the surface of inorganic ferrites. MHC maintained magnetic susceptibility regardless of reaction time at reaction temperature 250°C. Pronounced inhibitory effects of magnetic hydrochar occurred during start-up of AD but diminished with prolong AD times. Visible biofilms were observed on the MHC by laser scanning microscope after AD.

Hydrothermal carbonization (HTC) of wheat straw: influence of feedwater pH prepared by acetic acid and potassium hydroxide.

In this study, influence of feedwater pH (2-12) was studied for hydrothermal carbonization (HTC) of wheat straw at 200 and 260°C. Acetic acid and KOH were used as acidic and basic medium, respectively. Hydrochars were characterized by elemental and fiber analyses, SEM, surface area, pore volume and size, and ATR-FTIR, while HTC process liquids were analyzed by HPLC and GC. Both hydrochar and HTC process liquid qualities vary with feedwater pH. At acidic pH, cellulose and elemental carbon increase in hydrochar, while hemicellulose and pseudo-lignin decrease. Hydrochars produced at pH 2 feedwater has 2.7 times larger surface area than that produced at pH 12. It also has the largest pore volume (1.1 × 10(-1) ml g(-1)) and pore size (20.2 nm). Organic acids were increasing, while sugars were decreasing in case of basic feedwater, however, phenolic compounds were present only at 260°C and their concentrations were increasing in basic feedwater.

Behavior of selected hydrolyzed and dehydrated products during hydrothermal carbonization of biomass.

In this study, effects of reaction temperature and reaction time on both solid hydrochar and HTC process liquid products were studied for hydrothermal carbonization (HTC) of cellulose, wheat straw, and poplar. A novel slurry sampling system was designed and used with an 18.6L Parr reactor for 0-480 min in 200, 230, and 260 °C. Sugars (sucrose, glucose, and fructose), HMF, and furfural were found maximum in lower HTC temperature and time. However, they degrade following first order degradation kinetics. Activation energies of total sugars (glucose, fructose, sucrose, and xylose), furfural, and HMF for straw and poplar were 95-127, 130-135, and 74-90 kJ mol(-1), respectively and individuals were lower for HTC of cellulose than others. Organic acids (acetic acid, formic acid, and lactic acid) and phenolic compounds (phenol, catechol, and guaiacol) were increasing with higher HTC severity.

Evaluation of integrated anaerobic digestion and hydrothermal carbonization for bioenergy production.

Lignocellulosic biomass is one of the most abundant yet underutilized renewable energy resources. Both anaerobic digestion (AD) and hydrothermal carbonization (HTC) are promising technologies for bioenergy production from biomass in terms of biogas and HTC biochar, respectively. In this study, the combination of AD and HTC is proposed to increase overall bioenergy production. Wheat straw was anaerobically digested in a novel upflow anaerobic solid state reactor (UASS) in both mesophilic (37 °C) and thermophilic (55 °C) conditions. Wet digested from thermophilic AD was hydrothermally carbonized at 230 °C for 6 hr for HTC biochar production. At thermophilic temperature, the UASS system yields an average of 165 LCH4/kgVS (VS: volatile solids) and 121 L CH4/kgVS at mesophilic AD over the continuous operation of 200 days. Meanwhile, 43.4 g of HTC biochar with 29.6 MJ/kgdry_biochar was obtained from HTC of 1 kg digestate (dry basis) from mesophilic AD. The combination of AD and HTC, in this particular set of experiment yield 13.2 MJ of energy per 1 kg of dry wheat straw, which is at least 20% higher than HTC alone and 60.2% higher than AD only.

Hydrothermal carbonization (HTC): near infrared spectroscopy and partial least-squares regression for determination of selective components in HTC solid and liquid products derived from maize silage.

Near-infrared (NIR) spectroscopy was evaluated as a rapid method of predicting fiber components (hemicellulose, cellulose, lignin, and ash) and selective compounds of hydrochar and corresponding process liquor produced by hydrothermal carbonization (HTC) of maize silage. Several HTC reaction times and temperatures were applied and NIR spectra of both HTC solids and liquids were obtained and correlated with concentration determined from van-Soest fiber analysis, IC, and UHPLC. Partial least-squares regression was applied to calculate models for the prediction of selective substances. The model developed with the spectra had the best performance in 3-7 factors with a correlation coefficient, which varied between 0.9275-0.9880 and 0.9364-0.9957 for compounds in solid and liquid, respectively. Calculated root mean square errors of prediction (RMSEP) were 0.42-5.06mg/kg. The preliminary results indicate that NIR, a widely applied technique, might be applied to determine chemical compounds in HTC solid and liquid.

Reaction kinetics of hydrothermal carbonization of loblolly pine.

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed.

Pretreatment of rice hulls by ionic liquid dissolution.

As a highly available waste product, rice hulls could be a starting block in replacing liquid fossil fuels. However, their silica covering can make further use difficult. This preliminary study investigates effects of dissolving rice hulls in the ionic liquids 1-ethyl-3-methylimidazolium acetate (EMIM Ac), 1-hexyl-3-methylimidazolium chloride, (HMIM Cl), and 1-allyl-3-methylimidazolium chloride (AMIM Cl), and what lignocellulosic components can be precipitated from the used ionic liquid with water and ethanol. EMIM Ac dissolution at 110 °C for 8 h was found to completely remove lignin from rice hulls, while ethanol was capable of precipitating lignin out of the used EMIM Ac. With 8h dissolution at 110 °C using HMIM Cl, approximately 20% of the cellulose in the rice hull sample can be precipitated out using water as co-solvent, while more than 60% of the hemicellulose can be precipitated with ethanol.