•Model food waste was hydrothermal carbonized in DI, and 0.01N HCl, NaCl, and NaOH.•The adsorptive capacity of washed and unwashed hydrochars for atrazine was determined.•Calculated interaction ...energies show atrazine is more strongly adsorbed to surfaces without weakly associated alkyl groups.
Hydrothermal carbonization of simulated food waste was performed at 250°C for 20h using deionized water (DI) and 0.01N solutions of HCl, NaCl, and NaOH. The hydrochars produced were washed with acetone and the adsorptive capacity of the washed and unwashed hydrochars for atrazine were characterized. Using a generalized linear model, it was shown that the adsorptive capacity of the washed hydrochar was significantly higher than that of the unwashed hydrochars. The HCl processed unwashed hydrochar has a slightly higher adsorptive capacity compared to the DI processed hydrochar while both the NaOH processed washed and unwashed hydrochars were slightly lower than the corresponding DI processed hydrochars. 13C solid-state NMR results showed no discernible differences in surface functional groups among the washed hydrochars and among the unwashed hydrochars. A clear decrease in alkyl groups and an increase in aromatic/olefinic-C groups were observed after acetone washing. 1H liquid-phase NMR showed carbon alkyl chains were present in the acetone wash. Interaction energies calculated using dispersion corrected density functional theory show that atrazine is more strongly adsorbed to surfaces without weakly associated alkyl groups.
Hydrothermal carbonization (HTC) is a novel thermal conversion process that can be used to convert municipal waste streams into sterilized, value-added hydrochar. HTC has been mostly applied and ...studied on a limited number of feedstocks, ranging from pure substances to slightly more complex biomass such as wood, with an emphasis on nanostructure generation. There has been little work exploring the carbonization of complex waste streams or of utilizing HTC as a sustainable waste management technique. The objectives of this study were to evaluate the environmental implications associated with the carbonization of representative municipal waste streams (including gas and liquid products), to evaluate the physical, chemical, and thermal properties of the produced hydrochar, and to determine carbonization energetics associated with each waste stream. Results from batch carbonization experiments indicate 49–75% of the initially present carbon is retained within the char, while 20–37% and 2–11% of the carbon is transferred to the liquid- and gas-phases, respectively. The composition of the produced hydrochar suggests both dehydration and decarboxylation occur during carbonization, resulting in structures with high aromaticities. Process energetics suggest feedstock carbonization is exothermic.
•Carbonization of cellulose was conducted over time and at different temperatures.•The majority of cellulose conversion occurs between 0.5 and 4h.•Conversion is faster at higher ...temperatures.•Gas-phase hydrocarbon production increases with time.•Final solids recovered consist primarily of sp2 carbons and alkyl groups.
Studies have demonstrated that hydrothermal carbonization of biomass and waste streams results in the formation of beneficial materials/resources with minimal greenhouse gas production. Data necessary to understand how critical process conditions influence carbonization mechanisms, product formation, and associated environmental implications are currently lacking. The purpose of this work is to hydrothermally carbonize cellulose at different temperatures and to systematically sample over a 96-h period to determine how changes in reaction temperature influence product evolution. Understanding cellulose carbonization will provide insight to carbonization of cellulosic biomass and waste materials. Results from batch experiments indicate that the majority of cellulose conversion occurs between the first 0.5–4h, and faster conversion occurs at higher temperatures. Data collected over time suggest cellulose solubilization occurs prior to conversion. The composition of solids recovered after 96h is similar at all temperatures, consisting primarily of sp2 carbons (furanic and aromatic groups) and alkyl groups.
Functionalized graphene oxide (GO), derived from pure graphite via the modified Hummer method, was used to modify commercially available ceramic ultrafiltration membranes using the vacuum method. The ...modified ceramic membrane functionalized with GO (ceramicGO) was characterized using a variety of analysis techniques and exhibited higher hydrophilicity and increased negative charge compared with the pristine ceramic membrane. Although the pure water permeability of the ceramicGO membrane (14.4–58.6 L/m2 h/bar) was slightly lower than that of the pristine membrane (25.1–62.7 L/m2 h/bar), the removal efficiencies associated with hydrophobic attraction and charge effects were improved significantly after GO coating. Additionally, solute transport in the GO nanosheets of the ceramicGO membrane played a vital role in the retention of target compounds: natural organic matter (NOM; humic acid and tannic acid), pharmaceuticals (ibuprofen and sulfamethoxazole), and inorganic salts (NaCl, Na2SO4, CaCl2, and CaSO4). While the retention efficiencies of NOM, pharmaceuticals, and inorganic salts in the pristine membrane were 74.6%, 15.3%, and 2.9%, respectively, these increased to 93.5%, 51.0%, and 31.4% for the ceramicGO membrane. Consequently, the improved removal mechanisms of the membrane modified with functionalized GO nanosheets can provide efficient retention for water treatment under suboptimal environmental conditions of pH and ionic strength.
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•GO adsorptive properties were characterized by AFM, XRD, XPS, ZP, and DLS.•The sonication of GO significantly improved the removal of target compounds.•The main binding mechanisms ...were hydrophobic and π–π EDA interactions.
The adsorptive properties of graphene oxide (GO) were characterized, and the binding energies of diclofenac (DCF) and sulfamethoxazole (SMX) on GO adsorption were predicted using molecular modeling. The adsorption behaviors of DCF and SMX were investigated in terms of GO dosage, contact time, and pH. Additionally, the effects of sonication on GO adsorption were examined. GO adsorption involves “oxygen-containing functional groups” (OCFGs) such as COOH, which exhibit negative charges over a wide range of pH values (pH 3–11). DCF (−18.8kcalmol−1) had a more favorable binding energy on the GO surface than SMX (−15.9kcalmol−1). Both DCF and SMX were removed from solution (adsorbed to GO), up to 35% and 12%, respectively, within 6h, and an increase in GO dosage enhanced the removal of DCF. Electrostatic repulsion occurred between dissociated DCF/SMX and the more negatively charged GO at basic pH (>pKa). The sonication of GO significantly improved the removal of DCF (75%) and SMX (30%) due to dispersion of exfoliated GO particles and the reduction of OCFGs on the GO surface. Both DCF and SMX in the adsorption isotherm were explained well by the Freundlich model. The results of this study can be used to maximize the adsorption capacities of micropollutants using GO in water treatment processes.
•Life cycle assessment of the HTC process was conducted using EASETECH.•HTC products and hydrochar combustion influence system environmental impact.•Emission savings from electricity generated from ...hydrochar combustion are significant.•Liquid streams need to be appropriately managed to reduce environmental impact.•Sorting of food wastes from the waste stream reduces the load to the environment.
Although there are numerous studies suggesting hydrothermal carbonization is an environmentally advantageous process for transformation of wastes to value-added products, a systems level evaluation of the environmental impacts associated with hydrothermal carbonization and subsequent hydrochar combustion has not been conducted. The specific objectives of this work are to use a life cycle assessment approach to evaluate the environmental impacts associated with the HTC of food wastes and the subsequent combustion of the generated solid product (hydrochar) for energy production, and to understand how parameters and/or components associated with food waste carbonization and subsequent hydrochar combustion influence system environmental impact. Results from this analysis indicate that HTC process water emissions and hydrochar combustion most significantly influence system environmental impact, with a net negative GWP impact resulting for all evaluated substituted energy-sources except biomass. These results illustrate the importance of electricity production from hydrochar particularly when it is used to offset coal-based energy sources. HTC process water emissions result in a net impact to the environment, indicating a need for developing appropriate management strategies. Results from this analysis also highlight a need for additional exploration of liquid and gas-phase composition, a better understanding of how changes in carbonization conditions (e.g., reaction time and temperature) influence metal and nutrient fate, and the exploration of liquid-phase treatment.
•Hydrothermal carbonization (HTC) is a novel thermal conversion process.•HTC converts food wastes into value-added resources.•Carbonization integrates majority of carbon into solid-phase and results ...in a hydrochar with high energy density.•Packaging materials imparts greatest influence on solids energy content.•HTC is energetically favorable.
Hydrothermal carbonization (HTC) is a thermal conversion technique that converts food wastes and associated packaging materials to a valuable, energy-rich resource. Food waste collected from local restaurants was carbonized over time at different temperatures (225, 250 and 275°C) and solids concentrations to determine how process conditions influence carbonization product properties and composition. Experiments were also conducted to determine the influence of packaging material on food waste carbonization. Results indicate the majority of initial carbon remains integrated within the solid-phase at the solids concentrations and reaction temperatures evaluated. Initial solids concentration influences carbon distribution because of increased compound solubilization, while changes in reaction temperature imparted little change on carbon distribution. The presence of packaging materials significantly influences the energy content of the recovered solids. As the proportion of packaging materials increase, the energy content of recovered solids decreases because of the low energetic retention associated with the packaging materials. HTC results in net positive energy balances at all conditions, except at a 5% (dry wt.) solids concentration. Carbonization of food waste and associated packaging materials also results in net positive balances, but energy needs for solids post-processing are significant. Advantages associated with carbonization are not fully realized when only evaluating process energetics. A more detailed life cycle assessment is needed for a more complete comparison of processes.
Recent studies have shown the presence of endocrine disrupting compounds (EDCs) in seawater and brackish water, which could potentially complicate various seawater desalination treatment processes. ...In this study, the adsorption of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) by single walled carbon nanotubes (SWCNTs) was investigated. Solutions of artificial seawater, brackish water, and a combination of these two waters were prepared, in accordance with previously published composition data. Overall, the removal efficiency for EE2 (95–98%) was higher than BPA (75–80%), possibly because of its higher log KOW value. The adsorptive capacity of the SWCNTs remained relatively constant for the artificial source waters used in this study, suggesting that the changes in the composition of the water did not affect the overall adsorption of the EDCs. Adjusting the pH of the solutions from 3.5 to 11 showed a 22–26% decrease in the adsorption of BPA, whereas no notable changes were found in the adsorption of EE2. Changes in the ionic strength of the solutions by increasing the concentrations of Na+ and Ca2+ did not significantly affect the adsorption of BPA or EE2. The concentration of dissolved organic carbon (DOC), represented in this study by humic acid, had noticeable effects on the adsorption of BPA and EE2. As the concentration of DOC increased, the removal of BPA and EE2 decreased by 5–15%, which could possibly be explained by competitive adsorption between the EDCs and humic acid. With increasing concentrations of SWCNTs, adsorption of DOC occurred with removal efficiencies of up to 95%. Hydrophobic interactions and π–π electron donor–acceptor (EDA) interactions among the EDCs, the DOC, and the SWCNTs have been hypothesized as the potential adsorption mechanisms for BPA and EE2.
► We study the adsorption of BPA and EE2 from seawater and brackish water onto SWCNTs. ► The adsorptive capacity of the SWCNTs was consistently higher for EE2 than for BPA. ► The influential parameters on the adsorption of EDCs onto SWCNTs were pH and calcium.
•Influence of changes in initial process water on carbonization were evaluated.•Changes in initial water pH and organic content influenced carbonization kinetics.•High concentrations of CaCl2 ...influenced carbonization mechanisms.•Initial process water pH and organics imparted little influence on carbonization.
Hydrothermal carbonization (HTC) is a thermal conversion process that has been shown to be environmentally and energetically advantageous for the conversion of wet feedstocks. Supplemental moisture, usually in the form of pure water, is added during carbonization to achieve feedstock submersion. To improve process sustainability, it is important to consider alternative supplemental moisture sources. Liquid waste streams may be ideal alternative liquid source candidates. Experiments were conducted to systematically evaluate how changes in pH, ionic strength, and organic carbon content of the initial process water influences cellulose carbonization. Results from the experiments conducted evaluating the influence of process water quality on carbonization indicate that changes in initial water quality do influence time-dependent carbonization product composition and yields. These results also suggest that using municipal and industrial wastewaters, with the exception of streams with high CaCl2 concentrations, may impart little influence on final carbonization products/yields.
The aggregation kinetics of nC60 and higher-order fullerene (HOF) clusters, i.e., nC70, nC76, and nC84, was systematically studied under a wide range of mono- (NaCl) and divalent (CaCl2) electrolytes ...and using time-resolved dynamic light scattering. Suwanee River Humic Acid (SRHA) was also used to determine the effect of natural macromolecules on nHOF aggregation. An increase in electrolyte concentration resulted in electrical double-layer compression of the negatively charged fullerene clusters, and the nC60s and nHOFs alike displayed classical Derjaguin–Landau–Verwey–Overbeek (DLVO) type interaction. The critical coagulation concentration (CCC) displayed a strong negative correlation with the carbon number in fullerenes and was estimated as 220, 150, 100, and 70 mM NaCl and 10, 12, 6, and 7.5 mM CaCl2 for nC60, nC70, nC76, and nC84, respectively. The aggregation mechanism (i.e., van der Waals interaction domination) was enumerated via molecular dynamics simulation and modified DLVO model. The presence of SRHA (2.5 mg TOC/L) profoundly influenced the aggregation behavior by stabilizing all fullerene clusters, even at a 100 mM NaCl concentration. The results from this study can be utilized to predict aggregation kinetics of nHOF clusters other than the ones studied here. The scaling factor for van der Waals interaction can also be used to model nHOF cluster interaction.
