Dong-Wan Cho

Carbon dioxide assisted sustainability enhancement of pyrolysis of waste biomass: A case study with spent coffee ground.

This work mainly presents the influence of CO2 as a reaction medium in the thermo-chemical process (pyrolysis) of waste biomass. Our experimental work mechanistically validated two key roles of CO2 in pyrolysis of biomass. For example, CO2 expedited the thermal cracking of volatile organic compounds (VOCs) evolved from the thermal degradation of spent coffee ground (SCG) and reacted with VOCs. This enhanced thermal cracking behavior and reaction triggered by CO2 directly led to the enhanced generation of CO (∼ 3000%) in the presence of CO2. As a result, this identified influence of CO2 also directly led to the substantial decrease (∼ 40-60%) of the condensable hydrocarbons (tar). Finally, the morphologic change of biochar was distinctive in the presence of CO2. Therefore, a series of the adsorption experiments with dye were conducted to preliminary explore the physico-chemical properties of biochar induced by CO2.

Adsorption Studies for the Removal of Nitrate Using Modified Lignite Granular Activated Carbon

The removal of nitrate on ZnCl2 modified lignite granular activated carbon (LGAC) was investigated. The LGAC was modified with varying chemical impregnation ratios (ZnCl2: LGAC) and activation temperatures. Modified LGAC (LGAC5), with a 2:1 chemical impregnation ratio and a 500°C activation temperature had the optimum adsorption capacity for , at a 200 mg/L initial concentration. The initial pH of the testing solutions significantly influenced the adsorption capacity of LGAC5. The contact time studies showed the effectiveness of LGAC5, up to 50 mg/L initial concentration with 30 min of equilibration time. Isotherm studies revealed the highest values of the Langmuir constant (b), confirming strong affinity of LGAC5 for ions. Thermodynamics studies verified the endothermic nature of the adsorption process with randomness at the solid/solution interface. Competitive ion testing demonstrated that interfering anions, such as Cl−, , significantly reduced adsorption on LGAC5.

The role of magnetite nanoparticles in the reduction of nitrate in groundwater by zero-valent iron

Magnetite nanoparticles were used as an additive material in a zero-valent iron (Fe0) reaction to reduce nitrate in groundwater and its effects on nitrate removal were investigated. The addition of nano-sized magnetite (NMT) to Fe0 reactor markedly increased nitrate reduction, with the rate proportionally increasing with NMT loading. Field emission scanning electron microscopy analysis revealed that NMT aggregates were evenly distributed and attached on the Fe0 surface due to their magnetic properties. The rate enhancement effect of NMT is presumed to arise from its role as a corrosion promoter for Fe0 corrosion as well as an electron mediator that facilitated electron transport from Fe0 to adsorbed nitrate. Nitrate reduction by Fe0 in the presence of NMT proceeded much faster in groundwater (GW) than in de-ionized water. The enhanced reduction of nitrate in GW was attributed to the adsorption or formation of surface complex by the cationic components in GW, i.e., Ca2+ and Mg2+, in the Fe0-H2O interface that promoted electrostatic attraction of nitrate to the reaction sites. Moreover, the addition of NMT imparted superior longevity to Fe0, enabling completion of four nitrate reduction cycles, which otherwise would have been inactivated during the first cycle without an addition of NMT. The results demonstrate the potential applicability of a Fe0/NMT system in the treatment of nitrate-contaminated GW.

The role of clay minerals in the reduction of nitrate in groundwater by zero-valent iron

Bench-scale batch experiments were performed to investigate the feasibility of using different types of clay minerals (bentonite, fullers earth, and biotite) with zero-valent iron for their potential utility in enhancing nitrate reduction and ammonium control. Kinetics experiments performed with deionized water (DW) and groundwater (GW) revealed nitrate reduction by Fe(0) proceeded at significantly faster rate in GW than in DW, and such a difference was attributed to the formation of green rust in GW. The amendment of the minerals at the dose of 25 g L(-1) in Fe(0) reaction in GW resulted in approximately 41%, 43%, and 33% more removal of nitrate in 64 h reaction for bentonite, fullers earth, and biotite, respectively, compared to Fe(0) alone reaction. The presumed role of the minerals in the rate enhancement was to provide sites for the formation of surface bound green rust. Bentonite and fullers earth also effectively removed ammonium produced from nitrate reduction by adsorption, with the removal efficiencies significantly increased with the increase in mineral dose above 5:1 Fe(0) to mineral mass ratio. Such a removal of ammonium was not observed for biotite, presumably due to its lack of swelling property. Equilibrium adsorption experiments indicated bentonite and fullers earth had maximum ammonium adsorption capacity of 5.6 and 2.1 mg g(-1), respectively.

The effect of granular ferric hydroxide amendment on the reduction of nitrate in groundwater by zero-valent iron

The feasibility of using granular ferric hydroxide (GFH) with zero-valent iron (Fe(0)) for its potential utility in enhancing nitrate reduction was investigated. The addition of 10gL(-1) GFH to 25gL(-1) Fe(0) significantly enhanced nitrate removal, resulting in 93% removal of 52.2mg-NL(-1) in 36-h as compared to 23% removal with Fe(0) alone. Surface analyses of the reacted Fe(0)/GFH revealed the presence of magnetite on the Fe(0) surface, which probably served as an electron mediator for nitrate reduction. Addition of GFH to Fe(0) also resulted in lower solution pH compared to Fe(0). The rate enhancing effect of GFH on nitrate reduction was attributed to the combined effects of magnetite formation and pH buffering by GFH. GFH amendment (100gL(-1)) significantly increased reduction capacity and longevity of Fe(0) to complete several nitrate reduction cycles before inactivation, giving a total nitrate removal of 205mg-NL(-1), while unamended Fe(0) gave only 20mg-NL(-1) before inactivation during the first reduction cycle. The overall result demonstrated the potential utility of Fe(0)/GFH system that may be developed into a viable technology for removal of nitrate from groundwater.

Reduction of Bromate by Cobalt-Impregnated Biochar Fabricated via Pyrolysis of Lignin Using CO2 as a Reaction Medium

In this study, pyrolysis of lignin impregnated with cobalt (Co) was conducted to fabricate a Co-biochar (i.e., Co/lignin biochar) for use as a catalyst for bromate (BrO3-) reduction. Carbon dioxide (CO2) was employed as a reaction medium in the pyrolysis to induce desired effects associated with CO2; (1) the enhanced thermal cracking of volatile organic compounds (VOCs) evolved from the thermal degradation of biomass, and (2) the direct reaction between CO2 and VOCs, which resulted in the enhanced generation of syngas (i.e., H2 and CO). This study placed main emphases on three parts: (1) the role of impregnated Co in pyrolysis of lignin in the presence of CO2, (2) the characterization of Co/lignin biochar, and (3) evaluation of catalytic capability of Co-lignin biochar in BrO3- reduction. The findings from the pyrolysis experiments strongly evidenced that the desired CO2 effects were strengthened due to catalytic effect of impregnated Co in lignin. For example, the enhanced generation of syngas from pyrolysis of Coimpregnated lignin in CO2 was more significant than the case without Co impregnation. Moreover, pyrolysis of Coimpregnated lignin in CO2 led to production of biochar of which surface area (599 m2 g-1) is nearly 100 times greater than the biochar produced in N2 (6.6 m2 g-1). Co/lignin biochar produced in CO2 also showed a great performance in catalyzing BrO3- reduction as compared to the biochar produced in N2.

Preparation of Calcined Zirconia-Carbon Composite from Metal Organic Frameworks and Its Application to Adsorption of Crystal Violet and Salicylic Acid

Zirconia-carbon (ZC) composites were prepared via calcination of Zr-based metal organic frameworks, UiO-66 and amino-functionalized UiO-66, under N2 atmosphere. The prepared composites were characterized using a series of instrumental analyses. The surface area of the ZC composites increased with the increase of calcination temperature, with the formation of a graphite oxide phase observed at 900 °C. The composites were used for adsorptive removal of a dye (crystal violet, CV) and a pharmaceutical and personal care product (salicylic acid, SA). The increase of the calcination temperature resulted in enhanced adsorption capability of the composites toward CV. The composite calcined at 900 °C exhibited a maximum uptake of 243 mg·g−1, which was much greater than that by a commercial activated carbon. The composite was also effective in SA adsorption (102 mg·g−1), and N-functionalization of the composite further enhanced its adsorption capability (109 mg·g−1). CV adsorption was weakly influenced by solution pH, but was more dependent on the surface area and pore volume of the ZC composite. Meanwhile, SA adsorption showed strong pH dependence, which implies an active role of electrostatic interactions in the adsorption process. Base-base repulsion and hydrogen bonding are also suggested to influence the adsorption of CV and SA, especially for the N-functionalized composite.

Fabrication of engineered biochar from paper mill sludge and its application into removal of arsenic and cadmium in acidic water

An engineered biochar was fabricated via paper mill sludge pyrolysis under CO2 atmosphere, and its adsorption capability for As(V) and Cd(II) in aqueous solution was evaluated in a batch mode. The characterization results revealed that the biochar had the structure of complex aggregates containing solid minerals (FeO, Fe3O4 and CaCO3) and graphitic carbon. Adsorption studies were carried out covering various parameters including pH effect, contact time, initial concentrations, competitive ions, and desorption. The adsorption of As(V) and Cd(II) reached apparent equilibrium at 180min, and followed the pseudo-second-order kinetics. The highest equilibrium uptakes of As(V) and Cd(II) were 22.8 and 41.6mgg-1, respectively. The adsorption isotherms were better described by Redlich-Peterson model. The decrease in As(V) adsorption was apparent with the increase in PO43- concentration, and a similar inhibition effect was observed for Cd(II) adsorption with Ni(II) ion. The feasibility of regeneration was demonstrated through desorption by NaOH or HCl.

Enhanced Reduction of Nitrate in Groundwater by Zero-valent Iron with Activated Red Mud

ABSTRACT The objective of this study was to examine the feasibility of using red mud for enhancing the nitrate removal in groundwater by zero-valent iron (Fe(0)). Batch experiments were performed with both untreated and acid-treated red mud in conjunction with Fe(0) system to treat an actual groundwater sample containing 2.52 mM nitrate. Addition of untreated red mud into aqueous solution containing Fe(0) abruptly raised pH value to highly alkaline (11–12.5), leading to inhibition of nitrate reduction. On the other hand, the addition of acid-treated red mud significantly increased nitrate removal, resulting in 164% increase in the 1st-order rate constant (kobs) as compared to Fe(0) alone system when the red mud was dosed at 5 g/L to the solution containing 50 g/L Fe(0). Nitrate removal increased with increasing dose of acid-treated red mud, showing nearly 100% increase in removal efficiency when the dose was increased from 0 to 0.5 g in 20 mL solutions containing 0.2 g Fe(0). The enhancing effect of activated red mud was assumed to be the result from scavenging of the reaction precipitate, thereby minimizing passivation of Fe(0) surfaces, and formation of additional reactive sites (e.g. green rust) for nitrate reduction. The reactions of both untreated and acid-treated red mud in the absence of Fe(0) showed little removal of nitrate, indicating red mud alone lacks reduction or sorption capability for nitrate. Results from this study demonstrated that the potential utility of Fe(0)/activated red mud system may be developed into a viable technology for the removal of nitrate from groundwater.

Adsorption of Pb(II) and Ni(II) from aqueous solution by nanosized graphite carbon-impregnated calcium alginate bead

A composite adsorbent was prepared by immobilizing nanosized graphite carbon, obtained from an electrochemical process, in calcium alginate beads to remove Pb(II) and Ni(II) from aqueous solution. Potential of the adsorbent was evaluated by comparing adsorption kinetics and capacity of the nanosized graphite carbon-impregnated calcium alginate beads (NGCAB) with those of the pure calcium alginate beads (AB) in batch experimental reactors. Kinetic studies indicated that both ions onto AB and NGCAB reached adsorption equilibria at 16 and 12 h, respectively, and the experimental kinetic data were well described by a pseudo-second-order regression model. Relatively rapid uptake of both ions occurred within the first 2 h, followed by slower sorption process which was well explained by the intraparticle diffusion model of Weber and Morris. The maximum equilibrium uptake of Pb(II) and Ni(II) by NGCAB with the initial concentration range of 903 and 1023 mg/L were approximately 460.9 and 93.3 mg/g, respectively. Adsorption isotherm of Pb(II) onto AB was well fitted by Langmuir isotherm model, while that of NGCAB showed a good prediction using the Freundlich isotherm model. The Freundlich isotherm model was more suitable to describe Ni(II) adsorption by both adsorbents. The overall results demonstrated a potential applicability of NGCAB for Pb(II) and Ni(II) removal from aqueous solutions.