An environmental impact assessment of quantum dot photovoltaics (QDPV) from raw material acquisition through use

Some emerging technologies are expected to be pivotal for solving many of the environmental challenges faced today, especially those related to energy. However, many of these technologies may incur significant environmental impacts over their life cycle, while having environmental benefits during their use. This paper presents results of a Life Cycle Assessment (LCA) of a proposed type of nanophotovoltaic, quantum dot photovoltaic (QDPV) module. The LCA is confined to the stages of raw materials acquisition, manufacturing, and use. The impacts of QDPV are compared with other types of PV modules and energy sources - both renewable and nonrenewable. To provide a comprehensive comparative assessment, QDPV modules were compared with mature as well as emerging PV types for which data are available. Comparative assessment with other types of energy sources includes coal, oil, lignite, natural gas, diesel, nuclear, wind, and hydropower.QDPV modules may have the potential to overcome two current barriers of solar technology: low efficiencies and high manufacturing costs. If higher efficiencies are realized, QDPV modules could pave the way to large scale implementation of solar energy, helping nations move toward greater energy independence. On the other hand, candidate materials as quantum dots for solar cell applications are mostly compound semiconductors such as cadmium selenide, cadmium telluride, and lead sulfide which may be toxic and for which renewable options are limited. Toxic effects of these materials may be exacerbated by their nanoscale features.The LCA was carried out using the software SimaPro, and the Ecoinvent Life Cycle Inventory (LCI) database supplemented with available literature and patent information. Our results indicate that while QDPV modules have shorter Energy PayBack Time (EPBT), lower Global Warming Potential (GWP), SO_x and NO_x emissions than other types of PV modules, they have higher heavy metal emissions, underscoring the need for investigation of emerging technologies, especially nano-based ones, from a life cycle perspective. QDPV modules are better in all impact categories assessed than carbon-based energy sources but they have longer EPBT than wind and hydropower and higher GWP.     

Uptake of arsenic by alkaline soils near alkaline coal fly ash disposal facilities

The attenuation of arsenic in groundwater near alkaline coal fly ash disposal facilities was evaluated by determining the uptake of arsenic from ash leachates by surrounding alkaline soils. Ten different alkaline soils near a retired coal fly ash impoundment were used in this study with pH ranging from 7.6 to 9.0, while representative coal fly ash samples from two different locations in the coal fly ash impoundment were used to produce two alkaline ash leachates with pH 7.4 and 8.2. The arsenic found in the ash leachates was present as arsenate [As(V)]. Adsorption isotherm experiments were carried out to determine the adsorption parameters required for predicting the uptake of arsenic from the ash leachates. For all soils and leachates, the adsorption of arsenic followed the Langmuir and Freundlich equations, indicative of the favorable adsorption of arsenic from leachates onto all soils. The uptake of arsenic was evaluated as a function of ash leachate characteristics and the soil components. The uptake of arsenic from alkaline ash leachates, which occurred mainly as calcium hydrogen arsenate, increased with increasing clay fraction of soil and with increasing soil organic matter of the alkaline soils. Appreciable uptake of arsenic from alkaline ash leachates with different pH and arsenic concentration was observed for the alkaline soils, thus attenuating the contamination of groundwater downstream of the retired coal fly ash impoundment.     

Spatial Variability of Different Fractions of Particulate Matter within an Urban Environment and between Urban and Rural Sites

ABSTRACT

The spatial variability of different fractions of particulate matter (PM) was investigated in the city of Basel, Switzerland, based on measurements performed throughout 1997 with a mobile monitoring station at six sites and permanently recorded measurements from a fixed site. Additionally, PM₁₀ measurements from the following year, which were concurrently recorded at two urban and two rural sites, were compared.

Generally, the spatial variability of PM₄, PM₁₀, and total suspended particulates (TSP) within this Swiss urban environment (area = 36 km²) was rather limited. With the exception of one site in a street canyon next to a traffic light, traffic density had only a weak tendency to increase the levels of PM. Mean PM₁₀ concentration at six sites with different traffic densities was in the range of less than ±10% of the mean urban PM₁₀ level. However, comparing the mean PM levels on workdays to that on weekends indicated that the impact of human activities, including traffic, on ambient PM levels may be considerable.

Differences in the daily PM₁₀ concentrations between urban and more elevated rural sites were strongly influenced by the stability of the atmosphere. In summer, when no persistent surface inversions exist, differences between urban and rural sites were rather small. It can therefore be concluded that spatial variability of annual mean PM concentration between urban and rural sites in the Basel area may more likely be caused by varying altitude than by distance to the city center.     

Reduction of dioxins and furanes by spray dryer absorption from incinerator flue gas

Reduction of gas phase polychlorinated dibenzodioxins and dibenzofuranes by spray dryer absorption from incinerator flue gas has been investigated. Results from pilot plant and industrial scale spray absorption systems are reported. The results show that conditions for very high removal efficiencies exist for all isomer groups. Total removal above 95% has been achieved.     

Compliance with and ecosystem function of biodiversity offsets in North American and European freshwaters

Land-use change via human development is a major driver of biodiversity loss. To reduce these impacts, billions of dollars are spent on biodiversity offsets. However, studies evaluating offset project effectiveness that examine components such as the overall compliance and function of projects remain rare. We reviewed 577 offsetting projects in freshwater ecosystems that included the metrics project size, type of aquatic system (e.g., wetland and creek), offsetting measure (e.g., enhancement, restoration, and creation), and an assessment of the projects’ compliance and functional success. Project information was obtained from scientific and government databases and gray literature. Despite considerable investment in offsetting projects, crucial problems persisted. Although compliance and function were related to each other, a high level of compliance did not guarantee a high degree of function. However, large projects relative to area had better function than small projects. Function improved when projects targeted productivity or specific ecosystem features and when multiple complementary management targets were in place. Restorative measures were more likely to achieve targets than creating entirely new ecosystems. Altogether the relationships we found highlight specific ecological processes that may help improve offsetting outcomes.     

A taxonomy of metrics for testing the industrial ecology hypotheses and application to design of freezer insulation

Industrial ecology is sometimes referred to as the science of sustainability, but unlike mature sciences, it has yet to establish reliable modes of inquiry or a uniform framework for dialogue—partly because sustainability is difficult to characterize, and partly because industry–environment interactions are difficult to model quantitatively. A number of sustainability metrics have recently been proposed that partially address the quantification problem, but inevitably oversimplify the problem of sustainability characterization. This paper proposes an overarching taxonomy for classifying the quantitative criteria of sustainability as financial, thermodynamic, environmental, ecological, socio-political or aggregated. Several examples are presented. Pollution potential, which is an environmental metric related to the ideal thermodynamic work (of mixing) per mole required to remove pollutants from the environment, is discussed in particular. However, because no single metric can capture sustainability per se, industrial ecology may be limited to elucidating the trade-offs that exist between different types of complementary (rather than substitutable) criteria. The life cycle of polyurethane foam insulation in freezer applications is presented as a quantitative example of how different environmental criteria can lead to different design recommendations. Lastly, the framework proposed herein suggests a research agenda for industrial ecology, especially regarding the linkages between different measures of sustainability and cross-comparison of the investigative methods found in different sciences related to sustainability.     

Advertising to the enemy: enhanced floral fragrance increases beetle attraction and reduces plant reproduction

Many organisms face challenges in avoiding predation while searching for mates. For plants, emitting floral fragrances to advertise reproductive structures could increase the attraction of detrimental insects along with pollinators. Very few studies have experimentally evaluated the costs and benefits of fragrance emission with explicit consideration of how plant fitness is affected by both pollinators and florivores. To determine the reproductive consequences of increasing the apparency of reproductive parts, we manipulated fragrance, pollination, and florivores in the wild Texas gourd, Cucurbita pepo var. texana. With enhanced fragrance we found an increase in the attraction of florivores, rather than pollinators, and a decrease in seed production. This study is the first to demonstrate that enhanced floral fragrance can increase the attraction of detrimental florivores and decrease plant reproduction, suggesting that florivory as well as pollination has shaped the evolution of floral scent.