Although many guidance documents have been developed to inform the design and operation of building water systems to ensure safe water quality, there is a lack of consensus on some topics. This study ...interviewed 22 subject matter experts (SMEs) to identify topics of concern for managing water quality in buildings and compared SME views with information available on these topics in 15 systematically screened important guidance documents. The study found 18 design and 11 operational topics as critical for managing water quality in buildings. No one guidance document addressed all these topics, suggesting that a compendium of available guidance is needed. SMEs most frequently recommended temperature and residual disinfectant measurements as good parameters for monitoring overall building water quality. Both SME and guidance document recommendations for temperature for controlling opportunistic pathogen growth were reasonably consistent with water heater setpoint >60 °C. However, hot water temperature recommendations varied between 50 and 55 °C for other locations (i.e., the water temperature at the tap or end of the return loop). On the contrary, recommendations for disinfectant residual levels (0.2–2.0 mg/L), flushing frequency (1–14 days), and allowable time for hot water to reach the tap (10–60 s) were not consistent. While this study was able to reconcile diverging views on some of the water quality topics, such as identifying common guidance for water heater set point to at least 60 °C, it also highlights lack of definitive guidance on other critical topics, such as residual level, flushing frequency, hot water time to tap, and the use of thermostatic mixing valves, indicating that these are significant knowledge gaps that need further investigation. The study concludes that there is a need for developing evidence-based guidance, particularly on the topics where expert opinions diverged.
District heating (DH) systems can improve energy efficiency, reduce greenhouse gas (GHG) emissions, and be a cost‐effective residential space heating alternative over conventional decentralized ...heating. This study uses radiative forcing (RF), a time‐sensitive life cycle assessment metric, to evaluate space heating alternatives. We compare forest residue and willow biomass resources and natural gas as fuel sources against decentralized heating using heating oil. The comparison is performed for selected locations in the Northeastern United States over a 30‐year production timeline and 100 observation years. The natural gas and willow scenarios are compared with scenarios where available forest residue is unused and adds a penalty of GHG emissions due to microbial decay. When forest residues are available, their use is recommended before considering willow production. Investment in bioenergy‐based DH with carbon capture and storage and natural‐gas‐based DH with carbon capture and storage (CCS) technology is considered to assess their influence on RF. Its implementation further improves the net carbon mitigation potential of DH despite the carbon and energy cost of CCS infrastructure. Soil carbon sequestration from willow production reduces RF overall, specifically when grown on land converted from cropland to pasture, hay, and grassland. The study places initial GHG emissions spikes from infrastructure and land‐use change into a temporal framework and shows a payback within the first 5 years of operation for DH with forest residues and willow.
Replacing conventional heating oil‐based decentralized residential heating with natural gas, forest residue, or willow feedstocks, and centralized‐district heating (DH) infrastructure significantly improves environmental performance. The study implements a temporal analysis using radiative forcing for 30 production years and 100 observation years, identifying the inflection points of greenhouse gas (GHG) emissions for the various residential heating feedstocks. Consideration of carbon capture and storage (CCS) and bioenergy CCS for natural gas and biomass‐based DH respectively shows significant atmospheric carbon capture. Such carbon capture technology supplements soil carbon sequestration‐based environmental GHG sequestration, for willow when grown on pasture, hay, and grasslands.
Renewable fuel standards for biofuels have been written into policy in the U.S. to reduce the greenhouse gas (GHG) intensity of transportation energy supply. Biofuel feedstocks sourced from within a ...regional market have the potential to also address sustainability goals. The U.S. Mid-Atlantic region could meet the advanced fuel designation specified in the Renewable Fuel Standard (RFS2), which requires a 50% reduction in GHG emissions relative to a gasoline baseline fuel, through ethanol produced from winter barley (Hordeum vulgare L.). We estimate technology configurations and winter barley grown on available winter fallow agricultural land in six Mid-Atlantic states. Using spatially weighted stochastic GHG emission estimates for winter barley supply from 374 counties and biorefinery data from a commercial dry-grind facility design with multiple co-products, we conclude that winter barley would meet RFS2 goals even with the U.S. EPA’s indirect land use change estimates. Using a conservative threshold for soil GHG emissions sourced from barley produced on winter fallow lands in the U.S. MidAtlantic, a biorefinery located near densely populated metropolitan areas in the Eastern U.S. seaboard could economically meet the requirements of an advanced biofuel with the co-production of CO2 for the soft drink industry.
Wastewater treatment plants (WWTPs) with anaerobic digestion of biosolids produce an ammonia-rich sidestream out of which nitrogen can be recovered through air stripping. Recovered ammonia can be ...used to produce ammonium sulfate (AS) for agricultural use, enabling the circular return of nitrogen as fertilizer to the food system. We investigate the cost and life cycle environmental impact of recovering ammonia from the sidestream of WWTPs for conversion to AS and compare it to AS production from the Haber Bosch process. We perform life cycle assessment (LCA) to investigate the environmental impact of AS fertilizer production by air-stripping ammonia from WWTP sidestreams at varying sidestream nitrogen concentrations. Techno-economic analysis (TEA) is performed to assess the break-even selling price of sidestream AS production at a WWTP in the City of Philadelphia. Greenhouse gas emissions for air-stripping technology range between 0.2 and 0.5 kg CO2e/kg AS, about six times lower than the hydrocarbon-based Haber-Bosch process, estimated at 2.5 kg CO2e/kg AS. Further reduction of greenhouse gas emissions is feasible by replacing fossil-based energy use in air-stripping process (82–98 % of net energy demand) with renewable sources. Also, a significant reduction in mineral depletion and improvement in human and ecosystem health are observed for the air-stripping approach. Furthermore, the break-even selling price for installing sidestream-based AS production at the Philadelphia's WWTP, considering capital and operating costs, is estimated at $0.046/kg AS (100 %), which is 92 % lower than the 2014 estimate of AS's average selling price at farms in the United States. We conclude that even with varying ammonia concentrations and high sidestream volume, air-stripping technology offers an environmentally and economically favorable option for implementing nitrogen recovery and simultaneous production of AS at WWTPs.
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•Environmental impact assessed for NH3 recovery from WWTP for (NH4)2SO4 production•Air-stripping evaluated for varying sidestream flow rate and NH3 concentrations•WWTP specific GHG emissions estimated to be 0.43 kg CO2e per kg (NH4)2SO4•Estimated Haber-Bosch GHG emissions are 6 times higher than if recovered from WWTP.•Break-even price estimated at $0.046 is 92 % lower than prevalent farm prices.
Renewable liquid fuels production from landfill waste provides a promising alternative to conventional carbon-intensive waste management methods and has the potential to contribute to the transition ...toward low-carbon fuel pathways. In this work, we investigated the life cycle greenhouse gas (GHG) emissions of producing Fischer-Tropsch diesel from landfill gas (LFG) using the TriFTS catalytic conversion process and compared it to fossil-based petroleum diesel. A life cycle-based comparison was made between TriFTS diesel and other LFG waste management pathways, LFG-to-Electricity and LFG-to-Compressed renewable natural gas (RNG), on a per kilogram of feedstock basis as well as on a per MJ of energy basis, which also included the LFG-to-Direct Combustion pathway. The study considered flaring of LFG as the common underlying counterfactual scenario for all of the waste-to-energy product pathways. We estimated the life cycle GHG emissions for TriFTS diesel to be -36.4 carbon dioxide equivalent (grams CO
e)/MJ which is significantly lower than its fossil fuel counterpart which was estimated to be 90.5 g CO
e/MJ on a cradle-to-grave basis. The life cycle emission results from both perspectives (per kg feedstock and per MJ energy output) show that TriFTS diesel is a viable alternative energy pathway from LFG when compared to other pathways, primarily due to the main product being a renewable fuel that can serve as a drop-in fuel for diesel-based uses, within both the waste industry as well as the larger market. Further sensitivity analysis was performed based on the production of TriFTS diesel with the counterfactual waste management scenario of LFG-to-Flaring as well as the alternative LFG-to-Electricity waste management pathway. The sensitivity of the carbon intensity for TriFTS diesel to flaring efficiency and the carbon intensity of the electricity grid were also investigated. The study highlights the potential for the TriFTS conversion process technology to contribute to the waste industry's closed loop and decarbonization initiatives and to provide low carbon fuel for transportation.
Agriculture faces key challenges of increasing productivity while reducing adverse impacts on the environment. Conventional practices that rely on tillage, inefficient and over‐application of ...chemicals, and monoculture row cropping are leading to growing resistance of weeds and pests to chemicals, nutrient and sediment run‐off, and declining soil carbon stocks in the United States. Digital technologies and artificial intelligence (AI) technologies are enabling the collection of vast amounts of geo‐referenced information about growing conditions within the field, automated implementation of spatially varying input applications, and reduced reliance on chemical inputs. We discuss the pathways by which digital agricultural technologies have the potential to address the challenge of herbicide‐resistant weeds, over‐application of nitrogen and irrigation water, and cover crop planting for restoring soil health and contribute to the environmental sustainability of agriculture. Then, we discuss the economic factors, behavioral preferences of farmers, peer pressure, and social networks that can be expected to play a role in adoption decisions. We conclude with a discussion of approaches for ex ante assessments of the determinants of farmer willingness to adopt digital technologies and their diffusion in a region.
Life Cycle Assessment (LCA) is a multi-faced analytical approach targeted to assess environmental and economic sustainability approaches. LCA is used to evaluate challenges faced by industrial ...processes objectively while identifying environmental, energy, and economic hot spots. Performing LCA, researchers face several challenges: data collection and missing data, spatial and temporal variability, selection of assessment metrics, and uncertainty.This thesis evaluates three different approaches to LCA applicable for bioenergy and marginal supply of nutrients for agriculture. Economic assessment is performed along with LCA to consider the feasibility of bioenergy and nutrient recovery pathways. Three primary objectives define the thesis consisting of: (a) combining LCA and economic assessment of air-stripping technology to evaluate the cost-effectiveness of producing ammonium sulfate (AS) fertilizer from anaerobic digestor effluent at wastewater treatment plants, (b) developing an optimization framework to assess barley-to-ethanol biofuel pathway for its relevance as an advanced fuel under the federal Renewable Fuel Standard (RFS2), and (c) evaluating forest residue and willow short-rotation crop feedstocks for residential heating as alternatives to the use of heating oil and natural gas.The study estimates a reduction of 83% in greenhouse gas emissions from AS if produced by air-stripping technology at Philadelphia’s WWTP compared to the conventional Haber Bosch process. Significant energy savings are observed for the ammonia recovery process compared to nitrogen and hydrogen's catalytic reaction to form ammonia in the Haber Bosch process. Economic evaluation considering capital and operational costs for Philadelphia’s WWTP flow capacities estimates a break-even selling price of $0.11 per gallon AS (100% w/w concentration). This study demonstrates a point estimation of LCA methodology to identify a prospective future technology's economic and environmental feasibility based on local parameters.In the second objective, an optimization framework is developed to minimize upstream feedstock costs of producing ethanol, which selects winter fallow cropland for growing barley for ethanol production. The framework uses simulations of soil greenhouse gas emissions and crop yield estimated from the DAYCENT biogeochemical model, where parameters related to weather cycle, soil properties, and fertilizer management options affect emissions and crop yield. A generalized additive mixed modeling approach is used to accommodate temporal and spatial autocorrelation and variation. A mixed-integer optimization approach is used to minimize upstream production cost while maximizing the cropland acreage per choice selection. As a case study, for a biorefinery producing 2.08 × 108 liters of barley-ethanol per year, the average carbon intensity is estimated at 0.74 gCO2e MJ−1 when all co-products are used. This shows that winter barley-to-ethanol can be classified as an advanced biofuel under RFS2. Credit incentives such as California state’s Low Carbon Fuel Standard are found to have a negligible effect on cropland selection. The study also found that the favored management approaches for reducing greenhouse gas emissions largely match the farmers’ choices to choose the most economical fertilizer management option.The third study implements Bern cycle modeling of atmospheric greenhouse gas retention and decomposition for estimating radiative forcing of alternative residential heating infrastructures over 30 production years and a total of 100 observation years. Natural gas and biomass feedstock-based heating scenarios are significantly more environmentally efficient than conventional heating oil. District heating (DH) infrastructure is similarly efficient as decentralized (CH) infrastructure for natural gas use. The study suggests using forest residues when available because if kept unused, it undergoes natural decay, emitting greenhouse gas emissions, which adversely affects radiative forcing for the 100 observed years. When forest residues are not available as feedstock, alternative bio-feedstock such as willow short rotation crop grown on marginal land can be planned for use in residential heating infrastructures. In addition, carbon capture and storage technology implementation can facilitate further reduction of radiative forcing when forest residues or willow short rotation crops are used as feedstocks. The study demonstrates the radiative forcing-based analytical framework that implements time-heterogenous greenhouse gas accounting of biomass-based residential heating.
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•Compost biofilter was exposed to steady and transient state operations.•Maximum elimination capacity was 91.2g/m3h at a total inlet load of 150.2g/m3h.•The presence of toluene ...inhibited benzene removal strongly at higher loading rates.•Main effects of process variables were statistically significant with low P values.•After prolonged periods of starvation, the biofilter was able to convalesce.
The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12–0.95g/m3), toluene (0.14–1.48g/m3) and gas-flow rate (0.024–0.072m3/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6–41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.
Based on a generalized Cellular Automata (CA) model which has the flexibility of reaction interactions between all possible two-agent combinations on both reactant and product side, in previous ...studies by the authors, probabilistic reaction events were combined in a multiplicative order and an exploratory study of the variability analysis was performed. However it was found that the probabilistic parameter values are extremely sensitive to the final model output. As such, NSGA-II based on a Multi-objective Genetic Algorithm (MOGA) is used in this study to obtain optimum sets of these probability parameter values within a feasible computational time. For each generation of the MOGA, the probability rules parameter values are updated (improved) based on the objective functions. Finally, a validation study is performed to indicate the applicability of the CA model to represent specific enzymatic reactions when coupled with the multi-objective optimization algorithm.
•Cellular automata are used to model enzymatic reaction kinetics on a 2D torus.•Fine-tuning the probabilities of reactions and movement is challenging.•A multi-objective genetic algorithm obtains the probabilities in feasible time.•A validation study indicates the applicability of the cellular automata model.
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