Eco-Design of a Wastewater Treatment System Based on Process Integration

Because almost all industrial plants have wastewater treatment systems, eco-design of the systems is an effective way to reduce environmental impacts and economic costs of industry sectors. The eco-design using biobjective optimization has, however, a limitation due to the subjective weighting on the two objectives. The objective of this study is to eco-design existing wastewater treatment systems based on process integration by converting biobjective to single objective problems. For the mathematical optimization model, an objective function is formulated by monetizing environmental impacts to external costs and summing the external and economic costs. Mass balances and constraints are formulated to reflect the superstructure model and real situations. Two case studies are performed to verify the developed model. The eco-design outcomes are compared to their respective economic cost- and environmental impact-minimized designs. This comparison shows that the developed model optimizes the trade-offs between the biobjectives. This study can be applied to reduce environmental impacts and economic costs of other process systems

Supermagnetically Tuned Halloysite Nanotubes Functionalized with Aminosilane for Covalent Laccase Immobilization

Halloysite nanotubes (HNTs) were tuned with supermagnetic Fe₃O₄ (M-HNTs) and functionalized with γ-aminopropyltriethoxysilane (APTES) (A-M-HNTs). Gluteraldehyde (GTA) was linked to A-M-HNTs (A-M-HNTs-GTA) and explored for covalent laccase immobilization. The structural characterization of M-HNTs, A-M-HNTs, and A-M-HNTs-GTA-immobilized laccase (A-M-HNTs-GTA-<i>Lac</i>) was determined by X-ray photoelectron spectroscopy, field-emission high-resolution transmission electron microscopy, a magnetic property measurement system, and thermogavimetric analyses. A-M-HNTs-GTA-<i>Lac</i> gave 90.20% activity recovery and a loading capability of 84.26 mg/g, with highly improved temperature and storage stabilities. Repeated usage of A-M-HNTs-GTA-<i>Lac</i> revealed a remarkably consistent relative activity of 80.49% until the ninth cycle. The A-M-HNTs-GTA-<i>Lac</i> gave consistent redox-mediated sulfamethoxazole (SMX) degradation up to the eighth cycle. In the presence of guaiacol, A-M-HNTs-GTA-<i>Lac</i> gave elevated SMX degradation compared with 2,2′-azinobis­(3-ethylbenzthiazoline-6-sulfonic acid) and syrinialdehyde. Therefore, the A-M-HNTs can serve as supermagnetic amino-functionalized nanoreactors for biomacromolecule immobilization. The obtained A-M-HNTs-GTA-<i>Lac</i> is an environmentally friendly biocatalyst for effective degradation of micropollutants, such as SMX, and can be easily retrieved from an aqueous solution by a magnet after decontamination of pollutants in water and wastewater

Effect of technology convergence for tablet PC on potential environmental impacts from heavy metals

<p>The technology convergence integrating multiple devices into a single one is now a distinct trend in electronic industry. This trend can lead to a decrease in the use of rare and toxic heavy metals due to resource sharing, or an increase due to the application of new and auxiliary technology. This study investigates the effect of technology convergence for tablet PC on hazardous waste, resource depletion, and toxicity potentials from heavy metals in electronic devices, considering how many single devices (i.e., netbook computer, electronic dictionary, mp3 player, digital camera, cell phone, and vehicle GPS system) can be displaced by a tablet PC depending on users. The hazardous waste potential from heavy metals is examined with existing U.S. federal and California state regulations, and the resource depletion and toxicity potentials from heavy metals are evaluated based on life cycle impact assessments. The potentials of a specific tablet PC are compared to the total of those of displaced single products. Overall, the tablet PC has lower hazardous waste, resource depletion, and toxicity potentials from heavy metals. However, in case the tablet PC displaces only two or three single devices, it requires more gold, molybdenum, and vanadium. Therefore, technology convergence should take into account materials consumption and user behavior to develop more sustainable products.</p

Comparative assessment of solar photovoltaic panels based on metal-derived hazardous waste, resource depletion, and toxicity potentials

<p>Solar photovoltaic (PV) cells are used to resolve energy security and climate change problems. Although PV panels have long physical lifetimes, they would be eventually replaced by new ones with higher energy efficiency and then changed to waste. Depending on the types of PV cells, waste PV panels have different environmental impact potentials due to different contents of substances. This study assesses and compares hazardous waste, resource depletion, and toxicity potentials from metals in three types of PV modules (i.e., polycrystalline silicon (Si), amorphous Si, and CIGS (copper/indium/gallium/di-selenite) PVs) on per-watt electricity generation basis. Hazardous waste potentials are examined by using metal leachability tests, and resource depletion and toxicity potentials are evaluated by using life cycle impact assessment methods. The polycrystalline Si and CIGS PVs have hazardous waste potentials due to lead (Pb) and cadmium/selenium, respectively, whereas the amorphous Si PV does not. The polycrystalline Si PV has the highest resource depletion potential due primarily to silver; the CIGS PV has the next highest due primarily to selenium; and the amorphous Si PV had the lowest, which is derived primarily from tin and copper. For toxicity potentials, overall the amorphous Si PV had lower potentials, derived primarily from barium/copper/nickel/zinc, than the polycrystalline Si and CIGS PVs of which the toxicity potentials were primarily form copper/lead/nickel/silver and copper/mercury/molybdenum/nickel/silver, respectively. Therefore, waste polycrystalline Si and CIGS PV panels should be recycled and managed with priority, and PV technology development needs to be directed to amorphous Si PV from the material perspective.</p

Two-Dimensional Ti₃C₂T_<i>x</i> MXene Nanosheets for Efficient Copper Removal from Water

The performance of two-dimensional (2D) Ti₃C₂T_<i>x</i> MXene nanosheets in the adsorption and copper removal from aqueous media was investigated. Delaminated (DL)-Ti₃C₂T_<i>x</i> exhibited excellent Cu removal ability, because of their large specific surface area, hydrophilicity, and unique surface functional properties. Scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analyses were performed to analyze the structural changes in Ti₃C₂T_<i>x</i> MXene and its interaction with Cu ions. Oxygenated moieties in the layered structure of MXene facilitated reductive adsorption of Cu²⁺ forming Cu₂O and CuO species. DL-Ti₃C₂T_<i>x</i> exhibited a higher and faster Cu uptake, compared to multilayer (ML)-Ti₃C₂T_<i>x</i>. The maximum experimental adsorption capacity (<i>Q</i>_exp,max) was 78.45 mg g^–1, and 80% of the total content of metal ions was adsorbed within 1 min. A pseudo-second-order kinetic model and the Freundlich adsorption isotherm accurately describe the equilibrium time and maximum Cu uptake onto the adsorbent material, respectively. Thermodynamic analysis revealed that the adsorption process was endothermic. The adsorption capacity (<i>Q</i>_e) of DL-Ti₃C₂T_<i>x</i> was 2.7 times higher than that of a commercially available activated carbon. The present results illustrate the promising potential of 2D MXene nanosheets for the removal of toxic metals from water