Algae biodiesel (BioD) and renewable diesel (RD) have been recognized as potential solutions to mitigating fossil-fuel consumption and the associated environmental issues. Life cycle assessment (LCA) has been used by many researchers to evaluate the potential environmental impacts of these algae-derived fuels, yielding a wide range of results and, in some cases, even differing on indicating whether these fuels are preferred to petroleum-derived fuels or not. This meta-analysis reviews the methodological preferences and results for energy consumption, greenhouse gas emissions, and water consumption for 54 LCA studies that considered algae BioD and RD. The significant variation in reported results can be primarily attributed to the difference in scope, assumptions, and data sources. To minimize the variation in life cycle inventory calculations, a harmonized inventory data set including both nominal and uncertainty data is calculated for each stage of the algae-derived fuel life cycle.

Continuous flow supercritical carbon dioxide (scCO2) was used to simultaneously extract, fractionate, and enrich simultaneously triacylglycerides (TAGs) of different carbon chain lengths and degrees of unsaturation from a 6-component mixture of analytical standards and from Chlorella sp., a common microalgae used as biodiesel feedstock. Evidence is presented that solubility for a given TAG can be enhanced or diminished in the presence of other, dissimilar TAGs due to solute to solute interactions and scCO2 densities. Comparison of analytical standard and Chlorella sp. extracts suggests that TAG mixtures and biomass matrices influence extraction behavior with the same TAG behaving differently depending on the starting material. This was validated by fitting Chrastil’s solubility parameters to indicate which TAGs were most susceptible to solute to solute interactions and neat CO2 density. A model was developed comparing the energy requirements for the downstream purification of TAGs trimyristin (C14:0), tripalmitin (C16:0), and trierucin (C22:1) from mixtures extracted with the scCO2 method developed here. The model outputs suggest trade-offs for over- or under-enriching certain TAGs using neat scCO2. Both the experimental and modeling results demonstrate the potential of scCO2 to be used as an initial fractionation and enrichment tool whereby the associated energy and economic costs of downstream processing, such as distillation, can be reduced.Keywords: Biorefinery; Energy analysis; Solubility separation

As the fifth global water footprint assessment, this study enhanced previous estimates of national blue water consumption (including fresh surface and groundwater) and main economic activities with (1) improved spatial and sectoral resolution and (2) quantified the impacts of virtual water trade on water use and water stress at both the national and basin level. In 2007, 1194 Gm3 of blue water was consumed globally for human purposes. The consuming (producing) of primary and manufactured goods and services from the sectors of “Primary Crops and Livestock”, “Primary Energy and Minerals”, “Processed Food and Beverages”, “Non-food Manufactured Products”, “Electricity”, “Commercial and Public Services”, and “Households” accounted for 33% (91%), ∼ 0% (1%), 37% (<1%), 13% (1%), 1% (2%), 15% (3%), and 2% (2%) of the world’s total blue water consumption, respectively. The considerable differences in sectoral water consumption accounted for by the two perspectives (consumption- vs production-based) highlight the significance of the water consumed indirectly, upstream in the supply chain (i.e., > 70% of total blue water consumption) while offering additional insights into the water implications of critical interconnected economic activities, such as the water-energy nexus. With 145 Gm3 (12%) of the blue water consumption embedded in the goods and services traded internationally, 89 countries analyzed were net blue water importers at the national level. On the basin level, the impacts of virtual water trade on water stress were statistically significant for basins across the world and within 104 countries; virtual water trade mitigated water stress for the basins within 85 of the 104 countries, including all of those where there are moderate and greater water stress countrywide (except Italy).

This study provides a more precise understanding of the main driving forces of anthropogenic water use across countries. The anthropogenic water use was distinguished as blue water (i.e., fresh surface and groundwater) and total water (i.e. blue + green water; green water is rainwater insofar as it does not become runoff) used for producing, consuming, exporting, and importing of primary and manufactured goods and services, measured on a per country and per capita basis. The population effect on national blue water consumption associated with producing and consuming was found to be bigger than what the commonly assumed unitary population elasticity indicates. Distinct from the homogeneous affluence-water relationships conventionally assumed, this study revealed varying and potentially opposite effects affluence can have depending on the water use account of interest (e.g., production-based or consumption-based, blue or green) and the income level. Affluence, not the availability of freshwater resources, was found to be the most critical driver of virtual water imports. And a more affluent lifestyle in high-income countries was still associated with greater blue water consumption. With each doubling of income, blue water embedded in the goods and services a nation consumed and imported on a per capita basis increased by 82% and 86%, respectively, across the 110 countries analyzed for 2007. In comparison to affluence, the varying per capita water consumption accounts across the nations were much less sensitive to food consumption patterns. Given its critical role for water, land, and energy use shown by this and previous studies, affluence should be taken as a critical factor in future studies to better understand and leverage the water-energy-food-land nexus.

Rainwater harvesting (RWH) systems implemented in office buildings under heterogeneous urban settings in the United States, including combined and separated storm sewer systems, will result in varying environmental and economic costs and benefits across multiple water sectors. The potable water saving and stormwater abatement potentials were found to strongly correlate with the local annual precipitation totals and patterns, specifically the long-period antecedent dry weather period. Given the current water rates and stormwater fees in large U.S. cities, RWH systems implemented in office buildings may not be cost-effective compared to the municipal supplies over their lifetime, except in Seattle, which has the highest stormwater fees in the country ($77.50/1000 sf impervious surface/month). The minimum net life cycle costs range from −$1.60 (Seattle) to $11.9 (Phoenix) per m3 of rainwater yield, resulting in a potential economic gain of over $520 (Seattle) to a net loss of $800 (Phoenix) per building annually. By preventing the rooftop runoff from entering the wastewater treatment plant, between 3 and 9 kg N eq per year could be reduced in combined sewer systems depending on local conditions. This N reduction comes at the expense 0.7–4.6 kg CO2 eq per m3 rainwater yield. In separate sewer systems, eutrophication reduction benefits result from reducing N loading associated with stormwater runoff. The overall sustainability of implementing RWH depends on the site-specific functional, economic, and environmental benefits, impacts, and trade-offs.

Industrial ecology has revolutionized our understanding of material stocks and flows in our economy and society. For this important discipline to have even deeper impact, we must understand the inherent nature of these materials in terms of human health and the environment. This paper focuses on methods to design synthetic chemicals to reduce their intrinsic ability to cause adverse consequence to the biosphere. Advances in the fields of computational chemistry and molecular toxicology in recent decades allow the development of predictive models that inform the design of molecules with reduced potential to be toxic to humans or the environment. The approach presented herein builds on the important work in quantitative structure–activity relationships by linking toxicological and chemical mechanistic insights to the identification of critical physical–chemical properties needed to be modified. This in silico approach yields design guidelines using boundary values for physiochemical properties. Acute aquatic toxicity serves as a model endpoint in this study. Defining value ranges for properties related to bioavailability and reactivity eliminates 99% of the chemicals in the highest concern for acute aquatic toxicity category. This approach and its future implementations are expected to yield very powerful tools for life cycle assessment practitioners and molecular designers that allow rapid assessment of multiple environmental and human health endpoints and inform modifications to minimize hazard.

Summary

One year ago, an industrial coal-processing liquid contaminated the Elk River in West Virginia and affected the tap water of 15% of the state's population. The spill was declared a federal disaster, and ongoing investigations remain. Last month, a report assessing the water and health impacts of the Elk River spill pointed to the lack of a sound scientific approach for responding to and recovering from such incidents.* This year also marks 5 years since the Deepwater Horizon oil spill in the Gulf of Mexico, and last month brought the 30-year anniversary of the Bhopal gas tragedy that killed thousands, considered the world's worst industrial disaster. Despite our best efforts and intentions, human-made chemicals continue to be released into the environment, often with unquantified and potentially unquantifiable deleterious consequences. The questions posed to science are how to better understand the nature of synthetic substances in order to predict their potential adverse impacts on humans and the biosphere, and how do we design future substances to eliminate the need for engineered control systems.

Multiwalled carbon nanotubes (MWNTs) are utilized in a number of sectors as a result of their favorable electronic properties. In addition, MWNT antimicrobial properties can be exploited or considered a potential liability depending on their intended application and handling. The ability to tailor electrochemical and antimicrobial properties using economical and conventional treatment processes introduces the potential to significantly enhance product performance. Oxygen functional groups are known to influence several MWNT properties, including redox activity. Here, MWNTs were functionalized with oxygen groups using standard acid treatments followed by selective reduction via annealing. Chemical derivatization coupled to X-ray photoelectron spectroscopy was utilized to quantify specific surface oxygen group concentration after variable treatment conditions, which were then correlated to observed trends in electrochemical and antimicrobial activities. These activities were evaluated as the potential for MWNTs to participate in the oxygen reduction reaction and to have the ability to promote the oxidation of glutathione. The compiled results strongly suggest that the reduction of surface carboxyl groups and the redox activity of carbonyl groups promote enhanced MWNT reactivity and elucidate the opportunity to design functional MWNTs for enhanced performance in their intended electrochemical or antimicrobial application.

A mixed carbon dioxide (CO2) and methanol (MeOH) system is shown to successfully transesterify triolein into methyl oleate at moderate pressures and temperatures below 100 °C in the presence of Nafion NR50, a heterogeneous catalyst. An experimental design was developed to explore the effects of mono-, bi-, and tri-phasic CO2–MeOH–triolein systems through pressure, temperature, and methanol loading, all of which influence the system phase behavior. It was found that one particular set of conditions (>80 °C, 9.5 MPa, 3.6% v/v reactor, ambient MeOH) demonstrated nearly complete yields due to the preferable phase behavior at these conditions. Cloud point curves of the ternary system (MeOH, CO2, and substrate, including triolein, diolein, monoolein, glycerol, and methyl oleate) are reported to describe this complex system phase behavior. Results indicate that optimized yields (>98% methyl oleate at 95 °C) are achieved when the reaction is carried out in a three-phase system (not including the solid catalyst as a separate phase), which can partially be attributed to increased solubility of triolein in methanol as well as increased mass transfer due to the presence of dissolved CO2.Keywords: Biodiesel; Carbon dioxide expanded liquid; Nafion; Transesterification

The potential applications as well as the environmental and human health implications of carbon nanomaterials are well represented in the literature. There has been a recent focus on how specific physicochemical properties influence carbon nanotube (CNT) function as well as cytotoxicity. The ultimate goal is a better understanding of the causal relationship between fundamental physiochemical properties and cytotoxic mechanism in order to both advance functional design and to minimize unintended consequences of CNTs. This study provides characterization data on a series of multiwalled carbon nanotubes (MWNTs) that underwent acid treatment followed by annealing at increasing temperatures, ranging from 400 to 900 °C. These results show that MWNTs can be imparted with the same toxicity as single-walled carbon nanotubes (SWNTs) by acid treatment and annealing. Further, we were able to correlate this toxicity to the chemical reactivity of the MWNT suggesting that it is a chemical rather than physical hazard. This informs the design of MWNT to be less hazardous or enables their implementation in antimicrobial applications. Given the reduced cost and ready dispersivity of MWNTs as compared to SWNTs, there is a significant opportunity to pursue the use of MWNTs in novel applications previously thought reserved for SWNTs.

A consequential life cycle assessment (LCA) is conducted to evaluate the trade-offs between water quality improvements and the incremental climate, resource, and economic costs of implementing green (bioretention basin, green roof, and permeable pavement) versus gray (municipal separate stormwater sewer systems, MS4) alternatives of stormwater infrastructure expansions against a baseline combined sewer system with combined sewer overflows in a typical Northeast US watershed for typical, dry, and wet years. Results show that bioretention basins can achieve water quality improvement goals (e.g., mitigating freshwater eutrophication) for the least climate and economic costs of 61 kg CO2 eq. and $98 per kg P eq. reduction, respectively. MS4 demonstrates the minimum life cycle fossil energy use of 42 kg oil eq. per kg P eq. reduction. When integrated with the expansion in stormwater infrastructure, implementation of advanced wastewater treatment processes can further reduce the impact of stormwater runoff on aquatic environment at a minimal environmental cost (77 kg CO2 eq. per kg P eq. reduction), which provides support and valuable insights for the further development of integrated management of stormwater and wastewater. The consideration of critical model parameters (i.e., precipitation intensity, land imperviousness, and infrastructure life expectancy) highlighted the importance and implications of varying local conditions and infrastructure characteristics on the costs and benefits of stormwater management. Of particular note is that the impact of MS4 on the local aquatic environment is highly dependent on local runoff quality indicating that a combined system of green infrastructure prior to MS4 potentially provides a more cost-effective improvement to local water quality.

The routine rational design of commercial chemicals with minimal toxicological hazard to humans and the environment is a key goal of green chemistry. The development of such a design strategy requires an understanding of the interrelationships between physical–chemical properties, structure, mechanisms and modes of action. This study develops property-based guidelines for the design of chemicals with reduced chronic aquatic toxicity to multiple standardized species and endpoints by exploring properties associated with bioavailability, narcotic toxicity and reactive modes of action, such as electrophilic interactions. Two simple properties emerge as key parameters that distinguish chemicals in the Low EPA level of concern to three aquatic species from those in the High level of concern – octanol–water partition coefficient, (log Po–w) and ΔE (LUMO–HOMO energy gap). Physicochemical properties were predicted using Schrodinger's QikProp, while frontier orbital energies were determined based on AM1 and DFT calculations using Gaussian03. Experimental toxicity data used consisted of chronic toxicity thresholds (NOEC) for Daphnia magna reproduction (317 compounds, 504 h-assay) and Oryzias latipes (Japanese medaka, 122 compounds in 336, 504 and 672 h assays) survival, and Pseudokirchneriella subcapitata, a green algae model (392 compounds). Results indicate that 92% of compounds of Low chronic concern have log Po–w values < 2 and ΔE > 9 eV. Chronically safe compounds to P. subcapitata meet similar criteria – 80% have log Po–w values < 3 and ΔE greater than 9 eV. Our work proposes design guidelines that can be used to significantly increase the probability that a chemical will have low chronic toxicity, based on the endpoints evaluated, to the three diverse aquatic species studied, and potentially to other aquatic species.

The addition of surface functional groups to single-walled carbon nanotubes (SWNTs) is realized as an opportunity to achieve enhanced functionality in the intended application. At the same time, several functionalized SWNTs (fSWNTs), compared to SWNTs, have been shown to exhibit decreased cytotoxicity. Therefore, this unique class of emerging nanomaterials offers the potential enhancement of SWNT applications and potentially simultaneous reduction of their negative human health and environmental impacts depending on the specific functionalization. Here, the percent cell viability loss of Escherichia coli K12 resulting from the interaction with nine fSWNTs, n-propylamine, phenylhydrazine, hydroxyl, phenydicarboxy, phenyl, sulfonic acid, n-butyl, diphenylcyclopropyl, and hydrazine SWNT, is presented. The functional groups range in molecular size, chemical composition, and physicochemical properties. While physiochemical characteristics of the fSWNTs did not correlate, either singularly or in combination, with the observed trend in cell viability, results from combined light scattering techniques (both dynamic and static) elucidate that the percent loss of cell viability can be correlated to fSWNT aggregate size distribution, or dispersity, as well as morphology. Specifically, when the aggregate size polydispersity, quantified as the width of the distribution curve, and the aggregate compactness, quantified by the fractal dimension, are taken together, we find that highly compact and narrowly distributed aggregate size are characteristics of fSWNTs that result in reduced cytotoxicity. The results presented here suggest that surface functionalization has an indirect effect on the bacterial cytotoxicity of SWNTs through the impact on aggregation state, both dispersity and morphology.

One of the most elusive yet significant goals of green chemistry is the routine design of commercially useful chemicals with reduced toxicological hazard. The main objective of this study was to derive property guidelines for the design of chemicals with reduced acute aquatic toxicity to multiple species. The properties explored included chemical solubilities, size, shape and molecular orbital energies. Physicochemical properties were predicted using Schrodinger's QikProp, while frontier orbital energies (HOMO, LUMO and HOMO–LUMO gap) were determined based on AM1 and DFT calculations using Gaussian03. Experimental toxicity data included acute toxicity thresholds (LC50) for the fathead minnow (Pimephales promelas; 570 compounds), the Japanese medaka (Oryzias latipes; 285 compounds), a cladoceran (Daphnia magna; 363 compounds) and green algae (Pseudokirchneriella subcapitata, 300 compounds). Mechanistically-driven qualitative and quantitative analyses between the in-silico predicted molecular properties and in vivo toxicity data were explored in order to propose property limits associated with higher probabilities of acutely safe chemicals. The analysis indicates that 70–80% of the compounds that have low or no acute aquatic toxicity concern by EPA guidelines to the four species have a defined range of values for octanol-water partition coefficient (logPo/w) and ΔE (LUMO–HOMO gap). Compounds with logPo/w values less than 2 and ΔE (AM1) greater than 9 eV are significantly more likely to have low acute aquatic toxicity compared to compounds that do not meet these criteria. These results are mechanistically rationalized. Our work proposes design guidelines that can be used to significantly increase the probability that a chemical will have low acute toxicity to the four species studied, and potentially other aquatic species.

Supercritical carbon dioxide (scCO2) was used to extract components of interest from Scenedesmus dimorphus, a microalgae species, under varied algal harvesting and extraction conditions. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the concentration of fatty acid methyl esters (FAME) and the FAME profile of transesterified lipids, phospholipids and pigments extracted under varied supercritical temperatures and pressures. The scCO2 extraction results are compared with conventional solvent extraction to evaluate differences in the efficiency and nature of the extracted materials. Algae harvested by centrifugation (vs.lyophilization) demonstrated a similar extraction efficiency in scCO2, indicating potential energy benefits by avoiding conventional algal mass dehydration prior to extraction. Centrifuged algae and optimized extraction conditions (6000 psi; 100 °C) resulted in comparable FAME yields to conventional processes, as well as increased selectivity, reflected in the decreased pigment, nitrogen and phospholipid contamination of the FAME. Cell pre-treatments—sonication, microwave, bead beating and lyophilization—showed an enhancement in extraction yield in both conventional solvent and scCO2 extraction, allowing for improved extraction efficiencies. This study suggests that scCO2, a green solvent, shows great potential for algal lipid extraction for the sustainable production of biodiesel.

The degradation and partitioning of sucralose during exposure to a variety of environmental and advanced treatment processes (ATP) and the effect of sucralose on indicator plant species were systematically assessed. Bench scale experiments were used to reproduce conditions from environmental processes (microbial degradation, hydrolysis, soil sorption) and ATPs (chlorination, ozonation, sorption to activated carbon, and UV radiation). Degradation only occurred to a limited extent during hydrolysis, ozonation, and microbial processes indicating that breakdown of sucralose will likely be slow and incomplete leading to accumulation in surface waters. Further, the persistence of sucralose was compared to suggested human tracer compounds, caffeine and acesulfame-K. In comparison sucralose exhibits similar or enhanced characteristics pertaining to persistence, prevalence, and facile detection and can therefore be considered an ideal tracer for anthropogenic activity. Ecological effects of sucralose were assessed by measuring sucrose uptake inhibition in plant cotelydons and aquatic plant growth impairment. Sucralose did not inhibit plant cotelydon sucrose uptake, nor did it effect frond number, wet weight, or growth rate in aquatic plant, Lemna gibba. Though sucralose does not appear toxic to plant growth, the peristent qualities of sucralose may lead to chronic low-dose exposure with largely unknown consequences for human and environmental health.

The use of algae as a feedstock for biodiesel production is a rapidly growing industry, in the United States and globally. A life cycle assessment (LCA) is presented that compares various methods, either proposed or under development, for algal biodiesel to inform the most promising pathways for sustainable full-scale production. For this analysis, the system is divided into five distinct process steps: (1) microalgae cultivation, (2) harvesting and/or dewatering, (3) lipid extraction, (4) conversion (transesterification) into biodiesel, and (5) byproduct management. A number of technology options are considered for each process step and various technology combinations are assessed for their life cycle environmental impacts. The optimal option for each process step is selected yielding a best case scenario, comprised of a flat panel enclosed photobioreactor and direct transesterification of algal cells with supercritical methanol. For a functional unit of 10 GJ biodiesel, the best case production system yields a cumulative energy demand savings of more than 65 GJ, reduces water consumption by 585 m3 and decreases greenhouse gas emissions by 86% compared to a base case scenario typical of early industrial practices, highlighting the importance of technological innovation in algae processing and providing guidance on promising production pathways.

A sustainable supply of both energy and water is critical to long-term national security, effective climate policy, natural resource sustainability, and social wellbeing. These two critical resources are inextricably and reciprocally linked; the production of energy requires large volumes of water, while the treatment and distribution of water is also significantly dependent upon energy. In this paper, a hybrid analysis approach is proposed to estimate embodied energy and to perform a structural path analysis of drinking water supply systems. The applicability of this approach is then tested through a case study of a large municipal water utility (city of Kalamazoo) in the Great Lakes region to provide insights on the issues of water-energy pricing and carbon footprints. Kalamazoo drinking water requires approximately 9.2 MJ/m3 of energy to produce, 30% of which is associated with indirect inputs such as system construction and treatment chemicals.

Historically, there is evidence to suggest that communities in the developing world have used plant-based materials as one strategy for purifying drinking water. In this study, the coagulant properties of Opuntia spp., a species of cactus, are quantitatively evaluated for the first time. Opuntia spp. was evaluated for turbidity removal from synthetic water samples, and steps were made toward elucidating the underlying coagulation mechanism. In model turbid water using kaolin clay particles at pH 10, Opuntia spp. reduced turbidity by 98% for a range of initial turbidities. This is similar to the observed coagulation activities previously described for Moringa oleifera, a widely studied natural coagulant. Although it has been reported that Moringa oleifera predominantly operates through charge neutralization, comparison of zeta potential measurements and transmission electron microscopy images of flocs formed by Opuntia spp. suggest that these natural coagulants operate through different mechanisms. It is suggested that Opuntia spp. operates predominantly through a bridging coagulation mechanism. Once optimized, application of these readily available plants as a part of point-of-use water treatment technology may offer a practical, inexpensive, and appropriate solution for producing potable water in some developing communities.

While fluorescent lighting is an important technology for reducing electrical energy demand, mercury used in the bulbs is an ongoing concern. Using state and country level data, net emissions of mercury from the marginal use of fluorescent lightbulbs are examined for a base year of 2004 for each of the 50 United States and 130 countries. Combustion of coal for electric power generation is generally the largest source of atmospheric mercury pollution; reduction in electricity demand from the substitution of incandescent bulbs with fluorescents leads to reduced mercury emissions during the use of the bulb. This analysis considers the local mix of power sources, coal quality, thermal conversion efficiencies, distribution losses, and any mercury control technologies that might be in place. Emissions of mercury from production and end-of-life treatment of the bulbs are also considered, providing a life-cycle perspective. Net reductions in mercury over the entire life cycle range from −1.2 to 97 mg per bulb depending on the country. The consequences for atmospheric mercury emissions of several policy scenarios are also discussed.

With the world’s largest population and consistently rapid rates of economic growth, China faces a choice of whether it will move towards a more sustainable development trajectory. This paper identifies the different factors driving innovation in the fields of green chemistry and green engineering in China, which we find to be largely driven by energy efficiency policy, increasingly strict enforcement of pollution regulations, and national attention to cleaner production concepts, such as “circular economy.” We also identify seven key barriers to the development and implementation of green chemistry and engineering in China. They are (1) competition between economic growth and environmental agendas, (2) regulatory and bureaucratic barriers, (3) availability of research funding, (4) technical barriers, (5) workforce training, (6) industrial engineering capacity, and (7) economic and financial barriers. Our analysis reveals that the most crucial barriers to green chemistry and engineering innovations in China appear to be those that arise from competing priorities of economic growth and environmental protection as well as the technical challenges that arise from possessing a smaller base of experienced human capital. We find that there is a great deal of potential for both the development of the underlying science, as well as its implementation throughout the chemical enterprise, especially if investment occurs before problems of technological lock-in and sunk costs emerge.Highlights► We identify factors driving green chemistry and green engineering in China. ► We analyze barriers to adoption of these technologies. ► Change is driven by multiple policies and direct investment. ► Development is hindered by capacity and short-term focus. ► There is a current window of opportunity for investment and technology change.