The concept of the water-food-energy nexus has been widely studied in the past decade. In this paper we expand on this concept to include environmental, economic, and social aspects as well as life ...cycle assessment based thinking. We proposed a set of Environmental Footprint Assessment, Life Cycle Assessment, and Socio-Economic Assessment indicators and calculated them using a developed System Dynamic Model for Water-Land-Food-Energy-Environment-Economic-Social Nexus (SD-WLF3ESN). The developed model was applied to predict the WLF3ESN of the corn crop in the Western Lake Erie Basin (WLEB)-USA for the period 2016-2030. The prediction was based on scenarios for population, land, yield, crop use, and crop production costs and returns at the county level of WLEB. A matrix for WLF3ESN of the corn crop in WLEB was developed. This matrix can help in developing policies and strategies for managing the nexus in the basin.
With solar photovoltaics (PV) playing an increasing role in our global energy market, it is now timely and critical to understand the end of life management of the solar panels. Recycling the panels ...can be an important pathway, possibly recovering a considerable amount of materials and adding economic benefits from currently installed solar panels. Yet, to date, the costs and benefits of recycling, especially when externality costs resulting from environmental pollution are considered, are largely unknown. In this study, we quantified the private and externality costs and benefits of recycling crystalline silicon (c-Si) PV panels. We found that the private cost of end-of-life (EoL) management of the c-Si PV module is USD 6.7/m2 and much of this cost is from transporting (USD 3.3/m2) and landfilling (USD 3.1/m2), while the actual recycling process (the cost of consumed materials, electricity or the investment for the recycling facilities) is very small (USD 0.3/m2). We found that the external cost of PV EoL management is very similar to the private cost (USD 5.2/m2). Unlike the breakdown of the private costs, much of the externality costs (USD 4.08/m2) come from the recycling process, which suggests that more environmentally friendly methods (e.g., recycling methods that involve fewer toxic chemicals, acids, etc.) should be preferred. We estimated that the total economic value of the recycled materials from c-Si PV waste is USD 13.6/m2. This means that when externality costs are not considered, the net benefit of recycling is USD 6.7; when the externality cost of recycling is considered, there is still a net benefit of USD 1.19 per m2.
•Composting toilets can be an alternative to flush based sanitation.•Many different composting toilet designs are available.•Composting is affected by moisture content, temperature, carbon to ...nitrogen ratio.•There are many barriers to composting toilets.•Research is needed in science based design of composting toilets.
In today’s flush based urban sanitation systems, toilets are connected to both the centralized water and wastewater infrastructures. This approach is not a sustainable use of our water and energy resources. In addition, in the U.S., there is a shortfall in funding for maintenance and upgrade of the water and wastewater infrastructures. The goal of this paper was to review the current knowledge on composting toilets since this technology is decentralized, requires no water, creates a value product (fertilizer) and can possibly reduce the burden on the current infrastructure as a sustainable sanitation approach. We found a large variety of composting toilet designs and categorized the different types of toilets as being self contained or central; single or multi chamber; waterless or with water/foam flush, electric or non-electric, and no-mix or combined collection. Factors reported as affecting the composting process and their optimum values were identified as; aeration, moisture content (50–60%), temperature (40–65°C), carbon to nitrogen ratio (25–35), pH (5.5–8.0), and porosity (35–50%). Mass and energy balance models have been created for the composting process. However there is a literature gap in the use of this knowledge in design and operation of composting toilets. To evaluate the stability and safety of compost for use as fertilizer, various methods are available and the temperature–time criterion approach is the most common one used. There are many barriers to the use of composting toilets in urban settings including public acceptance, regulations, and lack of knowledge and experience in composting toilet design and operation and program operation.
Water management plays a major role in any city, but applying alternative strategies might be more or less feasible depending on the urban form and water demand. This paper aims to compare the ...environmental performance of implementing rainwater harvesting (RWH) systems in American and European cities. To do so, two neighborhoods with a water-stressed Mediterranean climate were selected in contrasting cities, i.e., Calafell (Catalonia, Spain) and Ukiah (California, US). Calafell is a high-density, tourist city, whereas Ukiah is a typical sprawled area. We studied the life cycle impacts of RWH in urban contexts by using runoff modeling before (i.e. business as usual) and after the implementation of this system. In general, cisterns were able to supply >75% of the rainwater demand for laundry and toilet flushing. The exception were multi-story buildings with roofs smaller than 200m2, where the catchment area was insufficient to meet demand. The implementation of RWH was environmentally beneficial with respect to the business-as-usual scenario, especially because of reduced runoff treatment needs. Along with soil features, roof area and water demand were major parameters that affected this reduction. RWH systems are more attractive in Calafell, which had 60% lower impacts than in Ukiah. Therefore, high-density areas can potentially benefit more from RWH than sprawled cities.
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•We combined hydrologic modeling and life cycle assessment for rainwater management.•Two neighborhoods were compared based on urban form and water demand.•Rainwater harvesting reduced stormwater runoff and offered environmental benefits.•Higher urban density and water demand increase the benefits of rainwater harvesting.
Urban agriculture has emerged as an alternative to conventional rural agriculture seeking to foster a sustainable circular economy in cities. When considering the feasibility of urban agriculture and ...planning for the future of food production and energy, it is important to understand the relationships between energy flows throughout the system, identify their strengths and weaknesses, and make suggestions to optimize the system. To address this need, we analyzed the energy flows for growing tomatoes at a rooftop greenhouse (RTG). We used life cycle assessment (LCA) to identify the flows within the supply chain. We further analyzed these flows using ecological network analysis (ENA), which allowed a comparison of the industrial system to natural systems. Going beyond LCA, ENA also allowed us to focus more on the relationships between components. Similar to existing ENA studies on urban metabolism, our results showed that the RTG does not mimic the perfect pyramidal structure found in natural ecosystems due to the system's dependency on fossil fuels throughout the supply chain and each industry's significant impact on wasted energy. However, it was discovered that the RTG has strong foundational relationships in its industries, demonstrating overall positive utility; this foundation can be improved by using more renewable energy and increasing the recycling rates throughout the supply chain, which will in turn improve the hierarchy of energy flows and overall energy consumption performance of the system.
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•The energy-food nexus in urban agriculture was studied through interindustry flows.•We conducted an ecological network analysis using life cycle data.•An integrated rooftop greenhouse was assessed as an innovative case study.•The energy trophic structure does not mimic efficient natural metabolic systems.•Energy dissipation could be improved through renewable energy.
The potential release of toxic metals from damaged emerging photovoltaic (PV) cells has raised concerns about the safe use of these new types of PVs. In this study, this concern was addressed by ...analysing the life cycle toxicity of metals (cadmium, copper, lead, nickel, tin and zinc) that are commonly used in emerging PVs. In estimating the potential metal release, a new model that incorporates field conditions (crack size, time, and glass thickness) and physiochemical properties (diffusion coefficient and solubility product) was introduced. The results show that the use phase toxicity of copper and lead can be higher than the extraction phase toxicity. Thus, precautionary loss limits to manage toxic impacts from the use phase were proposed. Also, the toxicity from different layers of perovskite, copper zinc tin sulphide (CZTS), and quantum dot (QD) type of solar cells was compared. It was found that cadmium sulphide (compared to zinc oxide and tin oxide) and lead (II) sulphide (compared to lead (II) iodine and CZTS) were less toxic alternatives for the electron selective layer and light absorber, respectively. Finally, in comparing the toxic metal releases of the PVs to today's coal power plants, it was seen that the metal emissions from PVs are expected to be several times less than the emissions from coal.
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•Toxic metals can be released from photovoltaic cells during the use.•We introduced a theoretical model to find the leaching rate of metals.•We addressed the toxicity concerns regarding the safe use of PVs by analyzing the metals.•The CuSCN and PbI2 can leach out quickly, thus, cause high toxicity during the use phase.•Precautionary loss limits to manage toxic impacts from the use phase should be used.
Emerging photovoltaic (PV) technologies have a potential to address the shortcomings of today’s energy market which heavily depends on the use of fossil fuels for electricity generation. We created ...inventories that offer insights into the environmental impacts and cost of all the materials used in emerging PV technologies, including perovskites, polymers, Cu2ZnSnS4 (CZTS), carbon nanotubes (CNT), and quantum dots. The results show that the CO2 emissions associated with the absorber layers are much less than the CO2 emissions associated with the contact and charge selective layers. The CdS (charge selective layer) and ITO (contact layer) have the highest environmental impacts compared to Al2O3, CuI, CuSCN, MoO3, NiO, poly (3-hexylthiophene-2,5-diyl (P3HT)), phenyl-C61-butyric acid methyl ester (PCBM), poly polystyrene sulfonate (PEDOT:PSS), SnO2, spiro-OMeTAD, and TiO2 (charge selective layers) and Al, Ag, Cu, FTO, Mo, ZnO:In, and ZnO/ZnO:Al (contact layers). The cost assessments show that the organic materials, such as polymer absorbers, CNT, P3HT and spiro-OMeTAD, are the most expensive materials. Inorganic materials would be more preferable to lower the cost of solar cells. All the remaining materials have a potential to be used in the commercial PV market. Finally, we analyzed the cost of PV materials based on their material intensity and CO2 emissions, and concluded that the perovskite absorber will be the most eco-efficient material that has the lowest cost and CO2 emissions.
Rainwater harvesting (RWH) is a decentralized approach to meet non-potable water supply needs and stormwater management goals. Life cycle environmental impacts of RWH systems have been reported in ...previous studies, but the effects of different building configurations and the type of sewer connections have not been fully studied. In this study, we aim to go beyond case studies by developing an approach that shows how RWH life cycle assessment (LCA) results change for different building roof areas, occupancies, and sewer connections. We propose and analyze the ratio of building occupancy to roof area which can be expressed as demand to supply (D/S) ratio to estimate life cycle greenhouse gas (GHG) emissions of implementing RWH system when the harvested rainwater is used to flush the toilets. Result showed that for all the building roof area to occupancy configurations considered in this study, RWH systems had lower GHG emissions except in some separate sewer scenarios. Size of the cistern, water savings as well as life cycle GHG emissions varied as a function of D/S ratio. It was found that changing roof area and occupancy have different effects on cistern size, water savings and life cycle GHG emissions measured with respect to D/S ratio. Water savings and cistern size increased until D/S equaled 1 and remained constant for higher value when roof area was constant. The duo were constant until D/S ratio of 1 and decreased for higher D/S value. Though minimum life cycle GHG emissions were noticed for spacious building, the maximum savings in emissions were noted at D/S ratio equal to or more than 1 when the building footprint was kept constant when the building was connected to a combined sewer network. For occupancy constant case, maximum savings were reported at D/S equal to 1. Similarly when the building was connected to a separate sewer network, minimum emissions as well as maximum savings were reported at lowest possible D/S value when the building footprint was constant and at D/S less than or equal to 1 when the occupancy was kept constant. A recommendation framework was provided based on the results obtained to help designers and practitioners design the RWH system to minimize GHG emissions.
•The life cycle GHG emissions of using rainwater harvesting (RWH) system depends on sewer connection.•A new factor (D/S ratio) was introduced that can be used to evaluate the life cycle impacts of RWH systems.•Water savings, size of cistern as well as GHG emission of RWH system varies as a function of D/S ratio.•For all the building roof area to occupancy configurations considered, using RWH systems lowered the GHG emissions.
Water-related diseases are a primary problem in Palestine where many residents revert to harvested rainwater as their primary water source due to water shortages within the area. From an ...environmental engineering perspective, it is already well known that certain situations (e.g., cross contamination) reduce drinking water quality and ultimately cause diseases in a population. In this study, we investigated the social practices and situations that may lead to lower disease occurrence. Towards this goal, we surveyed 382 residents in Yatta to collect data on the water-related diseases that they experienced and the specific situations that might affect the disease occurrences such as the residents’ practices (i) for maintaining a high quality of cistern water, (ii) for maintaining the environment around the cistern, and (iii) for managing the wastewater. In addition, we measured the physicochemical and microbiological parameters in cisterns to support the qualitative survey data. The measured parameters, including turbidity, salinity, free available chlorine, total
Coliforms
, and fecal
Coliforms
, were above Palestinian Standard Institution (PSI) and World Health Organization (WHO) guideline levels, suggesting a potential infectious hazard. The poor quality of the water was also observed by residents based on change in taste and by visually noting floating impurities, turbidity, and green coloration. Survey results showed that observations of the poor quality in cisterns and surrounding environment had statistically significant correlation with most of the water-related diseases. Additionally, frequently emptying the septic tank contributes to improving the observed water qualities. Therefore, residents should be encouraged to continue to observe the water quality in the cistern, improve the surrounding environment of cistern, and empty their septic tank frequently, to keep the water diseases away from their households.
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