Economic and Environmental Assessment of Office Building Rainwater Harvesting Systems in Various U.S. Cities

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

Energy–Water Nexus Analysis of Enhanced Water Supply Scenarios: A Regional Comparison of Tampa Bay, Florida, and San Diego, California

Increased water demand and scarce freshwater resources have forced communities to seek nontraditional water sources. These challenges are exacerbated in coastal communities, where population growth rates and densities in the United States are the highest. To understand the current management dilemma between constrained surface and groundwater sources and potential new water sources, Tampa Bay, Florida (TB), and San Diego, California (SD), were studied through 2030 accounting for changes in population, water demand, and electricity grid mix. These locations were chosen on the basis of their similar populations, land areas, economies, and water consumption characters as well as their coastal locations and rising contradictions between water demand and supply. Three scenarios were evaluated for each study area: (1) maximization of traditional supplies; (2) maximization of seawater desalination; and (3) maximization of nonpotable water reclamation. Three types of impacts were assessed: embodied energy, greenhouse gas (GHG) emission, and energy cost. SD was found to have higher embodied energy and energy cost but lower GHG emission than TB in most of its water infrastructure systems because of the differences between the electricity grid mixes and water resources of the two regions. Maximizing water reclamation was found to be better than increasing either traditional supplies or seawater desalination in both regions in terms of the three impact categories. The results further imply the importance of assessing the energy–water nexus when pursuing demand-side control targets or goals as well to ensure that the potentially most economical options are considered

Consequential Environmental and Economic Life Cycle Assessment of Green and Gray Stormwater Infrastructures for Combined Sewer Systems

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

Freshwater Vulnerability beyond Local Water Stress: Heterogeneous Effects of Water-Electricity Nexus Across the Continental United States

Human health and economic prosperity are vulnerable to freshwater shortage in many parts of the world. Despite a growing literature that examines the freshwater vulnerability in various spatiotemporal contexts, existing knowledge has been conventionally constrained by a territorial perspective. On the basis of spatial analyses of monthly water and electricity flows across 2110 watersheds and three interconnected power systems, this study investigates the water-electricity nexus (WEN)’s transboundary effects on freshwater vulnerability in the continental United States in 2014. The effects are shown to be considerable and heterogeneous across time and space. For at least one month a year, 58 million people living in water-abundant watersheds were exposed to additional freshwater vulnerability by relying on electricity generated by freshwater-cooled thermal energy conversion cycles in highly stressed watersheds; for 72 million people living in highly stressed watersheds, their freshwater vulnerability was mitigated by using imported electricity generated in water-abundant watersheds or power plants running dry cooling or using nonfreshwater for cooling purposes. On the country scale, the mitigation effects were the most significant during September and October, while the additional freshwater vulnerability was more significant in February, March, and December. Due to the WEN’s transboundary effects, overall, the freshwater vulnerability was slightly worsened within the Eastern Interconnection, substantially improved within the Western Interconnection, and least affected within the ERCOT Interconnection

A Free Energy Approach to the Prediction of Olefin and Epoxide Mutagenicity and Carcinogenicity

The mutagenic and carcinogenic effects of strong alkylating agents, such as epoxides, have been attributed to their ability to covalently bind DNA in vivo. Most olefins are readily oxidized to reactive epoxides by CytP450. In an effort to develop predictive models for olefin and epoxide mutagenicity, the ring openings of 15 halogen-, alkyl-, alkenyl-, and aryl-substituted epoxides were modeled by quantum-mechanical transition state calculations using MP2/6-31+G­(d,p) in the gas phase and in aqueous solution. Free energies of activation (Δ<i>G</i>^⧧) and free energies of reaction (Δ<i>G</i>_rxn) were computed for each epoxide in the series. This study finds that an aqueous solution Δ<i>G</i>_rxn threshold value of approximately −14.7 kcal/mol can be used to discern mutagenic/carcinogenic epoxides (Δ<i>G</i>_rxn < −14.7 kcal/mol) from nonmutagens/noncarcinogens (Δ<i>G</i>_rxn > −14.7 kcal/mol). The computed reaction thermodynamics are appropriate regardless of ring-opening mechanism in vivo and are thus proposed as an effective in silico screen and design guideline for decreasing potential mutagenicity and carcinogenicity of olefins and their respective epoxides

Realizing Comparable Oxidative and Cytotoxic Potential of Single- and Multiwalled Carbon Nanotubes through Annealing

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

Life Cycle Impacts and Benefits of a Carbon Nanotube-Enabled Chemical Gas Sensor

As for any emerging technology, it is critical to assess potential life cycle impacts prior to widespread adoption to prevent future unintended consequences. The subject of this life cycle study is a carbon nanotube-enabled chemical gas sensor, which is a highly complex, low nanomaterial-concentration application with the potential to impart significant human health benefits upon implementation. Thus, the net lifecycle trade-offs are quantified using an impact-benefit ratio (IBR) approach proposed herein, where an IBR < 1 indicates that the downstream benefits outweigh the upstream impacts. The cradle-to-gate assessment results indicate that the midpoint impacts associated with producing CNTs are marginal compared with those associated with the other manufacturing stages. The cumulative upstream impacts are further aggregated to units of disability-adjusted life years (DALYs) using ReCiPe end point analysis method and quantitatively compared with the potential downstream DALY benefits, as lives saved, during the use phase. The approach presented in this study provides a guiding framework and quantitative method intended to encourage the development of nanoenabled products that have the potential to realize a net environmental, health, or societal benefit

Life Cycle Payback Estimates of Nanosilver Enabled Textiles under Different Silver Loading, Release, And Laundering Scenarios Informed by Literature Review

Silver was utilized throughout history to prevent the growth of bacteria in food and wounds. Recently, nanoscale silver has been applied to consumer textiles (nAg-textiles) to eliminate the prevalence of odor-causing bacteria. In turn, it is proposed that consumers will launder these items less frequently thus, reducing the life cycle impacts. While previous studies report that laundering processes are associated with the greatest environmental impacts of these textiles, there is no data available to support the proposed shift in consumer laundering behavior. Here, the results from a comprehensive literature review of nAg-textile life cycle studies are used to inform a cradle-to-grave life cycle impact assessment. Rather than assuming shifts in consumer behavior, the impact assessment is conducted in such a way that considers all laundering scenarios to elucidate the potential for reduced laundering to enable realization of a net life cycle benefit. In addition to identifying the most impactful stages of the life cycle across nine-midpoint categories, a payback period and uncertainty analysis quantifies the reduction in lifetime launderings required to recover the impacts associated with nanoenabling the textile. Reduction of nAg-textile life cycle impacts is not straightforward and depends on the impact category considered

Toward safer multi-walled carbon nanotube design: Establishing a statistical model that relates surface charge and embryonic zebrafish mortality

<p>Given the increased utility and lack of consensus regarding carbon nanotube (CNT) environmental and human health hazards, there is a growing demand for guidelines that inform safer CNT design. In this study, the zebrafish (<i>Danio rerio</i>) model is utilized as a stable, sensitive biological system to evaluate the bioactivity of systematically modified and comprehensively characterized multi-walled carbon nanotubes (MWNTs). MWNTs were treated with strong acid to introduce oxygen functional groups, which were then systematically thermally reduced and removed using an inert temperature treatment. While 25 phenotypic endpoints were evaluated at 24 and 120 hours post-fertilization (hpf), high mortality at 24 hpf prevented further resolution of the mode of toxicity leading to mortality. Advanced multivariate statistical methods are employed to establish a model that identifies those MWNT physicochemical properties that best estimate the probability of observing an adverse outcome. The physicochemical properties considered in this study include surface charge, percent surface oxygen, dispersed aggregate size and morphology and electrochemical activity. Of the five physicochemical properties, surface charge, quantified as the point of zero charge (PZC), was determined as the best predictor of mortality at 24 hpf. From a design perspective, the identification of this property–hazard relationship establishes a foundation for the development of design guidelines for MWNTs with reduced hazard.</p

Microalgae Commercialization Using Renewable Lignocellulose Is Economically and Environmentally Viable

Conventional phototrophic cultivation for microalgae production suffers from low and unstable biomass productivity due to limited and unreliable light transmission outdoors. Alternatively, the use of a renewable lignocellulose-derived carbon source, cellulosic hydrolysate, offers a cost-effective and sustainable pathway to cultivate microalgae heterotrophically with high algal growth rate and terminal density. In this study, we evaluate the feasibility of cellulosic hydrolysate-mediated heterotrophic cultivation (Cel-HC) for microalgae production by performing economic and environmental comparisons with phototrophic cultivation through techno-economic analysis and life cycle assessment. We estimate a minimum selling price (MSP) of 4722 USD/t for producing high-purity microalgae through Cel-HC considering annual biomass productivity of 300 t (dry weight), which is competitive with the conventional phototrophic raceway pond system. Revenues from the lignocellulose-derived co-products, xylose and fulvic acid fertilizer, could further reduce the MSP to 2976 USD/t, highlighting the advantages of simultaneously producing high-value products and biofuels in an integrated biorefinery scheme. Further, Cel-HC exhibits lower environmental impacts, such as cumulative energy demand and greenhouse gas emissions, than phototrophic systems, revealing its potential to reduce the carbon intensity of algae-derived commodities. Our results demonstrate the economic and environmental competitiveness of heterotrophic microalgae production based on renewable bio-feedstock of lignocellulose