Min Jang

Reduced graphene oxide and Ag wrapped TiO2 photocatalyst for enhanced visible light photocatalysis

A well-organised reduced graphene oxide (RGO) and silver (Ag) wrapped TiO2 nano-hybrid was successfully achieved through a facile and easy route. The inherent characteristics of the synthesized RGO-Ag/TiO2 were revealed through crystalline phase, morphology, chemical composition, Raman scattering, UV-visible absorption, and photoluminescence analyses. The adopted synthesis route significantly controlled the uniform formation of silver nanoparticles and contributed for the absorption of light in the visible spectrum through localized surface plasmon resonance effects. The wrapped RGO nanosheets triggered the electron mobility and promoted visible light shift towards red spectrum. The accomplishment of synergised effect of RGO and Ag well degraded Bisphenol A under visible light irradiation with a removal efficiency of 61.9%.

Environmental behavior of engineered nanomaterials in porous media: a review

A pronounced increase in the use of nanotechnology has resulted in nanomaterials being released into the environment. Environmental exposure to the most common engineered nanomaterials (ENMs), such as carbon-based and metal-based nanomaterials, can occur directly via intentional injection for remediation purposes, release during the use of nanomaterial-containing consumer goods, or indirectly via different routes. Recent reviews have outlined potential risks assessments, toxicity, and life cycle analyses regarding ENM emission. In this review, inevitable release of ENMs and their environmental behaviors in aqueous porous media are discussed with an emphasis on influencing factors, including the physicochemical properties of ENMs, solution chemistry, soil hydraulic properties, and soil matrices. Major findings of laboratory column studies and numerical approaches for the transport of ENMs are addressed, and studies on the interaction between ENMs and heavy metal ions in aqueous soil environments are examined. Future research is also presented with specific research directions and outlooks.

Combined hydrous ferric oxide and quaternary ammonium surfactant tailoring of granular activated carbon for concurrent arsenate and perchlorate removal

Activated carbon was tailored with both iron and quaternary ammonium surfactants so as to concurrently remove both arsenate and perchlorate from groundwater. The iron (hydr)oxide preferentially removed the arsenate oxyanion but not perchlorate; while the quaternary ammonium preferentially removed the perchlorate oxyanion, but not the arsenate. The co-sorption of two anionic oxyanions via distinct mechanisms has yielded intriguing phenomena. Rapid small-scale column tests (RSSCTs) with these dually prepared media employed synthetic waters that were concurrently spiked with arsenate and perchlorate; and these trial results showed that the quaternary ammonium surfactants enhanced arsenate removal bed life by 25-50% when compared to activated carbon media that had been preloaded merely with iron (hydr)oxide; and the surfactant also enhanced the diffusion rate of arsenate per the Donnan effect. The authors also employed natural groundwater from Rutland, MA which contained 60 microg/L As and traces of silica, and sulfate; and the authors spiked this with 40 microg/L perchlorate. When processing this water, activated carbon that had been tailored with iron and cationic surfactant could treat 12,500 bed volumes before 10 microg/L arsenic breakthrough, and 4500 bed volumes before 6 microg/L perchlorate breakthrough. Although the quaternary ammonium surfactants exhibited only a slight capacity for removing arsenate, these surfactants did facilitate a more favorably positively charged avenue for the arsenate to diffuse through the media to the iron sorption site (i.e. via the Donnan effect).

Removal of humic and tannic acids by adsorption–coagulation combined systems with activated biochar

Despite recent interest in transforming biomass into bio-oil and syngas, there is inadequate information on the compatibility of byproducts (e.g., biochar) with agriculture and water purification infrastructures. A pyrolysis at 300°C yields efficient production of biochar, and its physicochemical properties can be improved by chemical activation, resulting in a suitable adsorbent for the removal of natural organic matter (NOM), including hydrophobic and hydrophilic substances, such as humic acids (HA) and tannic acids (TA), respectively. In this study, the adsorption affinities of different HA and TA combinations in NOM solutions were evaluated, and higher adsorption affinity of TA onto activated biochar (AB) produced in the laboratory was observed due to its superior chemisorption tendencies and size-exclusion effects compared with that of HA, whereas hydrophobic interactions between adsorbent and adsorbate were deficient. Assessment of the AB role in an adsorption-coagulation hybrid system as nuclei for coagulation in the presence of aluminum sulfate (alum) showed a synergistic effect in a HA-dominated NOM solution. An AB-alum hybrid system with a high proportion of HA in the NOM solution may be applicable as an end-of-pipe solution.

Application of Box-Behnken design with response surface methodology for modeling and optimizing ultrasonic oxidation of arsenite with H2O2

AbstractA combined ultrasound (US)/H2O2 process was used to oxidize arsenite to arsenate, yielding a synergistic effect value of 1.26. This showed that the combined process could be an effective method of oxidizing arsenite, instead of using either ultrasonic or H2O2 oxidation processes. This combined process was successfully modeled and optimized using a Box-Behnken design with response surface methodology (RSM). The effects of the US power density, the initial concentration of arsenite, and the H2O2 concentration on the sonochemical oxidation efficiency of arsenite were investigated. Analysis of variance indicated that the proposed quadratic model successfully interpreted the experimental data with coefficients of determination of R2 = 0.95 and adjusted R2 = 0.91. Through this model, we can predict and control the oxidation efficiency under different conditions. Furthermore, the optimal conditions for the oxidation of arsenite were found to be a US power density of 233.26 W L−1, an initial arsenite concentration of 0.5 mg L−1, and an H2O2 concentration of 74.29 mg L−1. The predicted oxidation efficiency obtained from the RSM under the optimal conditions was 88.95%. A confirmation test of the optimal conditions verified the validity of the model, yielding an oxidation efficiency of 90.1%.

Enhanced removal of dichloroacetonitrile from drinking water by the combination of solar-photocatalysis and ozonation

In this study, the photocatalytic ozonation process using either UV lamps with a wavelength close to a solar wavelength (UVsolar) or natural solar light was established to study the effects of the major operating parameters on the removal of a toxic disinfection by-product (DBP), dichloroacetonitrile (DCAN), from drinking water. Based on the test results of a bench system, the UVsolar/TiO2/O3 process had the highest DCAN-removal rate among the advanced oxidation processes (AOPs). The optimal TiO2 and ozone doses were 1gL(-1) and 1.13gL(-1)h(-1), respectively, while room temperature (20°C) produced the highest rate constant in the kinetic tests. The kinetic rate constants linearly increased when the UVsolar intensity increased in the range 4.6-25Wm(-2); however, it increased less at intensities higher than 25Wm(-2). The test results of the outdoor system showed that the solar/TiO2/O3 process provided complete removal of DCAN that was two times faster and had about 4.6 times higher energy efficiency than with solar/TiO2. As a green oxidation technique, solar photocatalytic ozonation could be a good alternative for treating recalcitrant and toxic organic pollutants, because it has high oxidation potential and low energy consumption compared to conventional AOPs.

A continuous pilot-scale system using coal-mine drainage sludge to treat acid mine drainage contaminated with high concentrations of Pb, Zn, and other heavy metals

A series of pilot-scale tests were conducted with a continuous system composed of a stirring tank reactor, settling tank, and sand filter. In order to treat acidic drainage from a Pb-Zn mine containing high levels of heavy metals, the potential use of coal-mine drainage sludge (CMDS) was examined. The pilot-scale tests showed that CMDS could effectively neutralize the acidic drainage due to its high alkalinity production. A previous study revealed that calcite and goethite contained in CMDS contributed to dissolutive coprecipitation and complexation with heavy metals. The continuous system not only has high removal efficiencies (97.2-99.8%), but also large total rate constants (K(total), 0.21-10.18h(-1)) for all heavy metals. More specifically, the pilot system has a much higher Zn(II) loading rate (45.3gm(-3)day(-1)) than other reference systems, such as aerobic wetland coupled with algal mats and anoxic limestone drains. The optimum conditions were found to be a CMDS loading of 280gL(-1) and a flow rate of 8Lday(-1), and the necessary quantity of CMDS was 91.3gL(-1)day(-1), as the replacement cycle of CMDS was determined to be 70 days.

Kinetic and thermodynamic studies of the adsorption of heavy metals on to a new adsorbent: coal mine drainage sludge

In this study, we investigated the application of sludge waste obtained from a coal mine drainage treatment facility that treats acid mine drainage (designated as AMD) from metal‐mine water. The coal mine drainage sludge (designated as CMDS), which contained 70% goethite and 30% calcite, was utilized as a sorption material for Cu(II) and Zn(II) removal from an aqueous solution of metallic mine drainage. The equilibriums and kinetics were investigated during a series of batch adsorption experiments. The Langmuir model was used to fit the equilibrium data, resulting in the best fits. The removal efficiencies were controlled by solution pH, temperature, initial concentration of heavy metal, sorbent amount and contact time. The pseudo‐second‐order kinetic model was used to fit the kinetic data, providing a good correlation with the experimental data. The results of a thermodynamic study showed that the activation energies (EA) were 3.75 and 1.75 kJ mol−1 for the adsorption of Cu(II) and Zn(II) on to CMDS at pH 5.5. These values of activation energy could correspond to physisorption. The positive values obtained for both the standard enthalpy change, Δ0, and the standard entropy change, ΔS0, suggest that the adsorption of Cu(II) and Zn(II) on to the CMDS was an endothermic reaction and that randomness increased at the solid–liquid interface during the adsorption of Cu(II) and Zn(II) on to the CMDS. The adsorption process also followed a pseudo‐second‐order kinetic model.

Sustainable Development in the Mining Sector and Its Evaluation Using Fuzzy AHP (Analytic Hierarchy Process) Approach

ABSTRACT Mining activities have not only provided positive impacts on eco-social development but also caused many adverse ones on social and environmental conditions. Measurement of sustainable development for this specific economic sector requires specific considerations and implements in a sustainable development concept. This paper provides essential information regarding sustainable development issues, sustainable development evaluation and the wide range of effective applications of the two multi-criteria approaches, analytic hierarchy process (AHP) and fuzzy AHP. The aims of this paper are to discuss the urgent tasks of sustainable development problems in the mining sector, and to suggest a potential and practical approach of fuzzy AHP in the evaluation of sustainable development for mining sector. Moreover, this paper discusses the strong possibility of fuzzy AHP approaches for designing a sustainability system in the mining sector and handling uncertainty in deriving the priorities of components in a mining sustainability system. Once sustainable development hierarchy, including criteria and their behavior indicators specific for the mining sector, is established, fuzzy theory and the concept of fuzzy AHP can be utilized in evaluation of priority for each component. The result could provide a useful foundation for further sustainability evaluation researches for the mining sector.

Rapid removal of fine particles from mine water using sequential processes of coagulation and flocculation

The processes of coagulation and flocculation using high molecular weight long‐chain polymers were applied to treat mine water having fine flocs of which about 93% of the total mass was less than 3.02 µm, representing the size distribution of fine particles. Six different combinations of acryl‐type anionic flocculants and polyamine‐type cationic coagulants were selected to conduct kinetic tests on turbidity removal in mine water. Optimization studies on the types and concentrations of the coagulant and flocculant showed that the highest rate of turbidity removal was obtained with 10 mg L−1 FL‐2949 (coagulant) and 12 mg L−1 A333E (flocculant), which was about 14.4 and 866.7 times higher than that obtained with A333E alone and that obtained through natural precipitation by gravity, respectively. With this optimized condition, the turbidity of mine water was reduced to 0 NTU within 20 min. Zeta potential measurements were conducted to elucidate the removal mechanism of the fine particles, and they revealed that there was a strong linear relationship between the removal rate of each pair of coagulant and flocculant application and the zeta potential differences that were obtained by subtracting the zeta potential of flocculant‐treated mine water from the zeta potential of coagulant‐treated mine water. Accordingly, through an optimization process, coagulation–flocculation by use of polymers could be advantageous to mine water treatment, because the process rapidly removes fine particles in mine water and only requires a small‐scale plant for set‐up purposes owing to the short retention time in the process.