Seong-Rin Lim

Potentials of macroalgae as feedstocks for biorefinery

Macroalgae, so-called seaweeds, have recently attracted attention as a possible feedstock for biorefinery. Since macroalgae contain various carbohydrates (which are distinctively different from those of terrestrial biomasses), thorough assessments of macroalgae-based refinery are essential to determine whether applying terrestrial-based technologies to macroalgae or developing completely new technologies is feasible. This comprehensive review was performed to show the potentials of macroalgae as biorefinery feedstocks. Their basic background information was introduced: taxonomical classification, habitat environment, and carbon reserve capacity. Their global production status showed that macroalgae can be mass-cultivated with currently available farming technology. Their various carbohydrate compositions implied that new microorganisms are needed to effectively saccharify macroalgal biomass. Up-to-date macroalgae conversion technologies for biochemicals and biofuels showed that molecular bioengineering would contribute to the success of macroalgae-based biorefinery. It was concluded that more research is required for the utilization of macroalgae as a new promising biomass for low-carbon economy.

Heavy metals removal by EDTA-functionalized chitosan graphene oxide nanocomposites

Graphene-based two-dimensional materials have been explored in a variety of applications, including the treatment of heavy-metal-rich water/wastewater. Ethylenediaminetetraacetic acid (EDTA)-functionalized magnetic chitosan (CS) graphene oxide (GO) nanocomposites (EDTA-MCS/GO) were synthesized using a reduction precipitation method and applied to the removal of heavy metals, such as Pb2+, Cu2+, and As3+, from aqueous solutions. The synthesized nanocomposite was characterized by FT-IR, XRD, SEM, MPMS, zeta-potential and BET analyses. The influence of various operating parameters, such as pH, temperature, metal ion concentration, and contact time on the removal of the metal ions, was investigated. Owing to the large specific surface area, hydrophilic behavior, and functional moieties, the magnetic nanocomposite demonstrated excellent removal ability with a maximum adsorption capacity of 206.52, 207.26, and 42.75 mg g−1 for Pb2+, Cu2+, and As3+, respectively. The equilibrium data was evaluated by Langmuir and Freundlich isotherms, while the heavy metal adsorption reaction kinetics was analyzed by Lagergren pseudo-first-order and pseudo-second-order kinetic models. The nanocomposite was reused in four successive adsorption–desorption cycles, revealing a good regeneration capacity of the adsorbent.

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

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.

Quantitative Sustainability Assessment of Seaweed Biomass as Bioethanol Feedstock

Since terrestrial biomass-based ethanol has environmental and economic vulnerability, seaweed-based bioethanol is emerging as a new biofuel. To investigate the sustainability of seaweeds as bioethanol feedstock, this study quantitatively assesses the energy, freshwater, and fertilizer requirements; land-related carbon balance; and bioethanol productivity of seaweed biomass through comparison with terrestrial biomass. Also, the metal resource potential of seaweeds is assessed because valuable metals can be recovered from seaweed fermentation residue. Compared to corn grain and stover, seaweeds exhibit competitive energy requirements and ethanol productivity. Seaweed cultivation does not incur carbon debt derived from land use change and requires less freshwater than corn grain but more than switchgrass in cultivation and fermentation. Seaweed cultivation also does not require fertilizer application despite the high content of nitrogen and phosphorus. Seaweeds exhibit high resource potential for gold and silver. Therefore, seaweed biomass has high potential as a sustainable bioethanol feedstock.

Potential resource and toxicity impacts from metals in waste electronic devices

As a result of the continuous release of new electronic devices, existing electronic devices are quickly made obsolete and rapidly become electronic waste (e-waste). Because e-waste contains a variety of metals, information about those metals with the potential for substantial environmental impact should be provided to manufacturers, recyclers, and disposers to proactively reduce this impact. This study assesses the resource and toxicity (i.e., cancer, noncancer, and ecotoxicity) potentials of various heavy metals commonly found in e-waste from laptop computers, liquid-crystal display (LCD) monitors, LCD TVs, plasma TVs, color cathode ray tube (CRT) TVs, and cell phones and then evaluates such potentials using life cycle impact-based methods. Resource potentials derive primarily from Cu, Sb, Ag, and Pb. Toxicity potentials derive primarily from Pb, Ni, and Hg for cancer toxicity; from Pb, Hg, Zn, and As for noncancer toxicity; and from Cu, Pb, Hg, and Zn for ecotoxicity. Therefore, managing these heavy metals should be a high priority in the design, recycling, and disposal stages of electronic devices.

Effect of Surfactant Impregnation into Chitosan Hydrogel Beads Formed by Sodium Dodecyl Sulfate Gelation for the Removal of Congo Red

The effect of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) impregnation into chitosan hydrogel beads formed by sodium dodecyl sulfate (SDS) gelation (CSB) was investigated for the adsorption of Congo red (CR) from aqueous solutions. An impregnation of CTAB at 0.1 wt% into CSB increased adsorption from 97.46 mg/g to 113.24 mg/g, while 0.5 wt% TX100 impregnation into CSB registered a very small increase from 112.56 mg/g to 115.64 mg/g. CSB/CTAB exhibited similar adsorption at all pH levels (4-9), but CSB and CSB/TX100 showed lower adsorption at higher pH values. The Sips isotherm model was the best fit for all bead varieties, and the Sips maximum adsorption capacity value of CSB/CTAB (271.74 mg/g) was higher than that for CSB/TX100 (242.72 mg/g) or CSB without surfactant impregnation (174.83 mg/g). The experimental kinetic values of all varieties of beads for CR adsorption followed a pseudo-first-order rate model better than a pseudo-second-order rate model.

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

ABSTRACT 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.

Application of a combined three-stage system for reclamation of tunnel construction wastewater

A combined three-stage system, (1) coagulation (2) zeocarbon filtration and (3) membrane filtration, a combination of microfiltration (MF) and reverse osmosis (RO), was investigated for reclamation of tunnel construction wastewater having a salinity of 10.8–12.9‰ and a concentration of suspended solids (SS) in the range of 264–1084 mg/L. The initial stages – coagulation, zeocarbon filtration and MF – served as a precursor to RO membrane filtration to successfully reduce water contaminants to less than 0.2 nephelometric turbidity units (NTU) of turbidity, thereby minimizing the potential for fouling. The RO system subsequently removed over 99% of remaining pollutants including ionic substances, resulting in less than 0.02 NTU turbidity, less than 0.04 mg/L total nitrogen (TN) and less than 0.01 mg/L total phosphorus (TP). Also, addition of an RO system markedly reduced high salt concentrations (high chloride (Cl−) concentrations) in the wastewater, exceeding 99% salt elimination. Thus, reclaimed water from our combined system met and exceeded currently regulatory quality standards for wastewater reuse (turbidity ≤ 2.0 NTU; TN ≤ 10 mg/L; TP ≤ 0.5 mg/L; Cl− ≤ 250 mg/L).