Cycle Water Use Research Articles

Technical, Environmental, and Economic Analysis Comparing Low-Carbon Industrial Process Heat Options in U.S. Poly(vinyl chloride) and Ethylene Manufacturing Facilities.

Electrification and clean hydrogen are promising low-carbon options for decarbonizing industrial process heat, which is an essential target for reducing sector-wide emissions. However, industrial processes with heat demand vary significantly across industries in terms of temperature requirements, capacities, and equipment, making it challenging to determine applications for low-carbon technologies that are technically and economically feasible. In this analysis, we develop a framework for evaluating life cycle emissions, water use, and cost impacts of electric and clean hydrogen process heat technologies and apply it in several case studies for plastics and petrochemical manufacturing industries in the United States. Our results show that industrial heat pumps could reduce emissions by 12-17% in a typical poly(vinyl chloride) (PVC) facility in certain locations currently, compared to conventional natural gas combustion, and that other electric technologies in PVC and ethylene production could reduce emissions by nearly 90% with a sufficiently decarbonized electric grid. Life cycle water use increases significantly in all low-carbon technology cases. The levelized cost of heat of viable low-carbon technologies ranges from 15 to 100% higher than conventional heating systems, primarily due to energy costs. We discuss results in the context of relevant policies that could be useful to manufacturing facilities and policymakers for aiding the transition to low-carbon process heat technologies.

Tradeoffs in life cycle water use and greenhouse gas emissions of hydrogen production pathways

Hydrogen has been promoted as a key component of global decarbonization efforts, with various past studies estimating carbon emissions for several production pathways, but little past work has considered its water resource needs. This life cycle analysis considers hydrogen production on a per-kilogram basis for 11 pathways, fossil and non-fossil. It also includes impacts of treating water to the required quality for hydrogen production. Greenhouse gas emissions results were in a range of −15 to +31 kg CO2e/kg H2 produced. Water consumption varied more widely, from about 7 to 55 kg water/kg H2 for fossil-based pathways and 530 to 3400 kg water/kg H2 for biomass-based pathways. Electrolysis with various renewable electricity scenarios were also modeled. Overall, there are challenging tradeoffs to be navigated to achieve a low carbon and water footprint in hydrogen economy.

Comparative analysis of drought-responsive physiological and transcriptome in broomcorn millet (Panicum miliaceum L.) genotypes with contrasting drought tolerance

Climate change has caused severe drought, affecting global crop production. Broomcorn millet is a drought-tolerant crop preferred for water-saving agriculture because of its short life cycle and high water use efficiency. This study evaluated the drought tolerance of 300 broomcorn millet varieties from 21 sources under well-watered, semi-arid conditions (Yulin, Shaanxi, China) and unwatered, arid conditions (Dunhuang, Gansu, China). Two broomcorn millet varieties with contrasting drought tolerance attributes, DT 43 (drought-tolerant) and DS 190 (drought-sensitive), were selected for comparative physiological and transcriptional assessment under the two drought stress conditions (polyethylene glycol 6000 [PEG-6000] and soil drought) and corresponding melatonin treatments. The two forms of drought stress decreased photosynthetic capacity and triggered transcriptome reprogramming in both broomcorn millet cultivars. However, PEG induced a more ‘severe’ and ‘rapid’ drought stress than the ‘milder’ and ‘slower’ soil moisture drought stress. Moreover, PEG stress caused severe growth arrest and photosynthesis inhibition, especially for DS190. About 61.38% and 48.78% differentially expressed genes (DEGs) were up-regulated in DT 43 under PEG and soil drought stresses, respectively. Moreover, 74.31% and 54.59% DEGs were up-regulated in DS 190 under PEG and soil drought stresses, respectively. Most DEGs in DT 43 were significantly enriched in hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling, and carbon metabolism pathways. However, most DEGs in DS 190 were enriched in plant photosynthesis, chlorophyll metabolism, and nitrogen metabolism pathways. Moreover, melatonin enhanced the drought resistance of the two genotypes, increasing photosynthetic and antioxidant enzyme activity and thus mitigating transcription response. Therefore, these unique mechanisms of enhancing drought resistance can improve bioenergy crops, especially for the cultivation of drought-tolerant varieties.

Water Consumption and Environmental Impact of Multifamily Residential Buildings: A Life Cycle Assessment Study

Water use in buildings accounts for a large share in global freshwater consumption where research on the impacts of life cycle water use receive little or no attention. Moreover, there is very limited knowledge regarding such impacts that focus on the life cycle emissions from water consumption in building environments in the world’s most water-stressed countries. Hence, this study attempted to quantify the environmental impacts of operational water use in a multi-family residential building through a life cycle assessment (LCA). A small part of a Middle Eastern country, Doha (Qatar), has been selected for the primary assessment, while water-use impact in Miami (Florida) was chosen as a second case study, as both locations fall into similar climate zone according to ASHRAE Climate Zone Map. The LCA score indicated much higher impacts in the Doha case study compared to Miami. The variation in the result is mainly attributed to the raw water treatment stage in Doha, which involves energy-intensive thermal desalination. Again, relative comparison of the annual water and electricity use impacts for the modeled building was performed at the final stage for both locations. Water use was attributable for 18% of the environmental impacts in Miami, while this value increased to 35% in Doha. This initial assembled LCA result will be beneficial to both water authorities and building research communities in establishing more sustainable water use policies for specific regions/countries that will ultimately benefit the overall building environment.

Evapotranspiration partitioning and its interannual variability over a winter wheat-summer maize rotation system in the North China Plain

Partitioning of evapotranspiration (ET) is important for understanding surface-atmosphere interactions, hydrological cycle, and plant water use strategy. Here, we applied seven widely used eddy covariance (EC)-based methods and 15-year EC measurements in a winter wheat-summer maize rotation cropland in North China Plain to partition ET into soil evaporation (E) and plant transpiration (T). Then the two-stage theory of bare soil evaporation was employed to evaluate these partitioning methods. This innovative evaluation approach is particularly suitable for this kind of ecosystem, requires no direct measurements of ET components, and avoids spatial mismatching between the source areas of reference values and EC-based ET. Combining the two-stage theory and the meta-analysis, we found that among seven partitioning methods, only the Transpiration Estimation Algorithm (TEA) (hereafter, N18 method) utilizing a machine learning approach not only simulated the dynamics of 14-day transpiration fraction of ET (T/ET) quite well, but also yielded reliable 14-day and mean growing season magnitudes of T/ET for both crops. Furthermore, we developed a new partitioning method based on the stomatal slope parameter in the optimality-based unified stomatal optimization (USO) model. The newly developed method showed similar performances with N18 method on partitioning ET of both crops at our site. By using the N18 method and the newly developed method, we revealed that the multi-year mean growing season T/ET (± standard deviation) was 0.72 ± 0.03 and 0.77 ± 0.04 for maize and wheat, respectively. For the interannual variability of ET and its components, only T of maize increased significantly during 2005–2019 at our site. Moreover, it was found that E had the highest interannual variability followed by T and then T/ET for both crops.

Consumptive life cycle water use of biomass-to-power plants with carbon capture and sequestration

Biomass-to-power conversion provides the most promising route to bioenergy with carbon capture and sequestration (BECCS). The objectives of this study are to estimate the water consumption of biomass-to-power plants with CCS and then quantify its variability and uncertainty on a life cycle basis. The fuel-based life cycle analysis reveals that compared to the case of complete coal combustion with CCS, co-firing biomass at coal-fired power plants with CCS significantly increases the life cycle blue water consumption, depending on the type, co-firing rate, and production location of biomass; and dedicated biomass combustion with CCS further increases the life cycle blue water consumption by a factor of more than 55. Among the numerous stages across both the coal and biomass fuel cycles, the biomass production is the dominant stage accounting for more than 70% of the life cycle blue water consumption for the co-firing path and about 98% for the dedicated biomass-to-power path. These results indicate the importance of advancing agricultural practices and technologies to reduce the overall water consumption. Large-scale BECCS deployment may pose a challenge for water sustainability. Thus, this study calls for a strong need for a close coordination of technology, resource, and policy in transition to a sustainable net-zero carbon energy future.

Life cycle water footprint comparison of biomass-to-hydrogen and coal-to-hydrogen processes

Water is essential for the industrial production of hydrogen. This study investigates the production of hydrogen from biomass and coal. To date, there are few studies focusing on the water footprint of biomass-to-hydrogen and coal-to-hydrogen processes. This research conducted a life cycle water use analysis on wheat straw biomass and coal to hydrogen via pyrolysis gasification processes. The results show that the water consumption of the entire biomass-to-hydrogen process was 76.77 L/MJ, of which biomass cultivation was the dominant contributor (99%). Conversely, the water consumption of the coal-to-hydrogen process was only 1.06 L/MJ, wherein the coal production stage accounted for only 4.15% for the total water consumption, which is far lower than that of the biomass-to-hydrogen process. The hydrogen production stage of biomass hydrogen production accounted for 76% of the total water consumption when excluding the water consumption of straw growth, whereas that of the coal hydrogen production stage was 96%. This research provides the associated water consumption, within a specified boundary, of both hydrogen production processes, and the influence of major factors on total water consumption was demonstrated using sensitivity analysis.

Influência de ondas de calor no desempenho agronômico do feijão no município de Campos Novos, em Santa Catarina

The aim of this study was to evaluate the influence of heat waves on the agronomic performance of beans in the municipality of Campos Novos, in Santa Catarina State, Brazil located in Southern Brazil. Daily data of maximum, minimum temperatures and rainfall from 1997 to 2011 from the Meteorological Station of Campos Novos were used. The data were analyzed in the Aquacrop 6.0 software to determine the cycle duration, biomass, yield and water use efficiency through evapotranspiration. In the three harvest years evaluated, it can be observed that heat waves tend to decrease cycle duration from one to three days and bean yield to 333kg/ha. The effects of heat waves on biomass production and on the efficiency of bean water use were uncertain because they may be linked to other constraints.

Evapotranspiration partitioning and water productivity of rainfed maize under contrasting mulching conditions in Northwest China

Soil mulching can effectively modify crop growth environments and increase crop productivity in rainfed agriculture, and the knowledge about water fluxes within the soil-crop-atmosphere ecosystem is essential for improving water productivity (WP) in water-limited regions such as Northwest China. This study systematically investigated seasonal and inter-annual dynamics of evapotranspiration (ET) partitioning into canopy interception (Ic), soil evaporation (Es) and plant transpiration (Tp) in rainfed maize fields under four mulching conditions (NM: non-mulching, SM: straw mulching, RPBF: plastic-mulched ridge with bare furrow, and RPSF: plastic-mulched ridge with straw-mulched furrow) from June to October in 2015, 2016 and 2017 characterized by various seasonal rainfall distributions. The results showed that seasonal ET was slightly higher under mulching conditions compared with NM during each growing season, but the difference was not statistically significant. Soil mulching decreased Es/ET (22.0–29.8 %, 14.3–19.5 % and 11.3–15.1 % under SM, RPBF and RPSF, respectively) relative to NM (27.6–34.5 %), while it increased Tp/ET (55.8–63.7 %, 63.0–71.0 % and 65.6–73.2 %, respectively) and Ic/ET (13.2–16.0 %, 14.7–17.4 % and 15.4–19.3 %, respectively) relative to NM (52.4–58.7 % and 13.0–15.7 %, respectively). Differences in ET partitioning under contrasting mulching conditions were related largely to variations in leaf area index and soil water stress. Although seasonal ET under various mulching conditions varied among the three seasons (264.8–286.6 mm in 2015, 241.2–242.5 mm in 2016 and 296.6–324.4 mm in 2017), the proportions of Ic (13.0–15.4 %, 13.3–19.3 % and 15.7–17.7 %), Es (11.3–28.3 %, 15.1–34.5 % and 11.4–27.6 %) and Tp (58.7–73.2 %, 52.4–65.6 % and 56.7–70.9 %) to total ET were similar. Soil mulching greatly enhanced maize yield by 9.5–26.1 %, 27.0–186.5 % and 30.8–209.7 % under SM, RPBF and RPSF compared with NM, respectively, resulting in 1.5–15.8 %, 19.0–184.7 % and 20.8–214.8 % higher WP, respectively. It was concluded that soil mulching largely promoted Tp and restrained Es in spite of slight increase in Ic, thereby improving maize yield and WP during the three seasons. The present study gives a better understanding of rainwater cycle and crop water use, which is critical to sustainable management of rainfed agriculture.

Spatially Allocating Life Cycle Water Use for US Coal‐Fired Electricity across Producers, Generators, and Consumers

There are water consequences across every life cycle stage of coal‐fired electricity consumption, from production and processing to combustion, which have not been studied with regional specificity. There is often a spatial decoupling between where coal is produced and processed versus where it is combusted for power generation, complicating any analysis to estimate the life cycle water implications of electricity consumption. Furthermore, electricity generated by coal‐fired power plants can be consumed within its own balancing authority or exported to another balancing authority. This analysis spatially resolves the water consumed and water withdrawn for coal mining, coal preparation, and power plant cooling from 1) where the coal is mined to where the coal is burned for power production and 2) where the electricity is generated to where the electricity is consumed. Although the largest portion of coal consumed came from the Northern Great Plains province, coal from this region consumes the least amount of water for mining and preparation compared with other provinces. Water withdrawals for cooling power plants within each balancing authority are driven by cooling technology. Due to the interconnected grid, there can be differences between attributing water footprint at the producer level versus the consumer level.

Life cycle assessment of ethanol production in a rice-straw-based biorefinery in India

This work presents detailed life cycle assessment (LCA) of a novel process to produce ethanol from rice straw in India. The process has been successfully demonstrated and proposed to be scaled-up, and detailed LCA of that process is the key novel contribution of this work. Cradle-to-gate system boundary is considered, which includes rice farming, transportation, and processing at the biorefinery. 1 l of ethanol is used as the functional unit. The process data are based on the demonstration-scale plant as well as the scale-up plant of 100 kilo litres per day being designed based on the same process. The life cycle inventory data are taken from the Ecoinvent® database. OpenLCA 1.6 is used to develop the LCA model, and impact assessment is performed using ILCD 2011 midpoint indicators. The GWP was 2.82 kg of CO2 eq. per liter of ethanol using economic impact allocation. Electricity contributed 86% of the total impact, and use of hydroelectricity reduced the impact to 0.07 kg of CO2 eq. per liter of ethanol. If additional benefits due to this process are considered, the impact reduced to − 0.392 kg of CO2 eq. per liter of ethanol indicating considerable relative reduction in the GWP. Without allocation and implementing system expansion, the impact was 3.35 kg of CO2 eq. per liter of ethanol. The energy return on investment was 1.59, indicating that the process was net energy positive. The lower bound on the life cycle water use was 507.4 l per liter of ethanol. The integrated nature of the process producing various value-added chemicals provided significant benefits from the perspective of environmental impacts.

Life cycle water use of gasoline and electric light-duty vehicles in China

The cradle-to-grave life cycle water withdrawal and consumption for typical light-duty gasoline and battery electric vehicles (BEVs) produced and operated in China is estimated for the first time. The life cycle withdrawal and consumption are 275 and 137 m3 for the gasoline, and 851 and 262 m3 for the electric Ford Focus (using national average grid electricity). The life cycle water estimates are dominated by water used for fuel production (gasoline or electricity). For the current national average grid, BEVs are more water intensive than conventional gasoline vehicles although the transition towards more solar and wind power will narrow this gap. The Focus BEV, if produced and operated on solar photovoltaic electricity, will have life cycle water withdrawal and consumption of 181 and 47 m3. Using wind electricity, the water withdrawal and consumption can be further reduced to 113 and 43 m3. Life cycle water withdrawal associated with vehicle use in China is approximately a factor of 2–4 lower than in the U.S. reflecting lower water withdrawal for electricity generation in China. Life cycle water consumption of BEVs in China is 50 % higher than in the U.S., mainly reflecting a greater share of hydroelectricity in China. In addition, large regional differences in electricity generation lead to a wide range in water use of BEVs. The results highlight the importance of a transition to renewable energy, particularly solar and wind, to power future sustainable electric mobility and improved energy and water use efficiency in BEV production.

Life Cycle Water Use for Oxy Fuel Combustion Power Generation with CO2 Capture and Storage

The water scarcity is becoming a growing concern. Regarded as a potential CO emission mitigation technology for coal-fired power plants, oxy-fuel combustion, a typical CCS technology, theoretically consumes a large amount of water, which increases the severity of the water scarcity. Therefore, revealing the water use of oxy-fuel coal-fired power plants is of great importance for the deployment of CCS technologies under water resource constraint in the future. In this respect, the aim of this study is to evaluate the life cycle water use of oxy-fuel CO capture, transport and storage via a 600 MW coal fired oxy-fuel power plant in China. By using a tiered hybrid life cycle assessment, both direct and indirect water use are calculated. Results show 22.9L H O/kg of CO and the oxy-fuel power plant stage dominates the total water use, while the water intensity for power generation is calculated as 3233.3 L H O/MWh, which is higher than the conventional power plants. Sensitivity analysis is performed in this research and indicates that the variation of tap water use affects the water intensity immensely. Furthermore, the use of the membrane method for air separation decreases the overall water use 14.21% respectively. China is continually increasing its efforts to reduce carbon emissions due to both domestic and international pressure. Hence the development and implement of the CCS technology is of great urgency. At the end of this study possible solutions such as using wasted or discarded wind power for the separation of oxygen to minimize water use in oxy-fuel power plant stage are put forward.

Water use of a biomass direct-combustion power generation system in China: A combination of life cycle assessment and water footprint analysis

Biomass combustion for power generation plays an important role in achieving 1.5 °C climate target and fulfilling global energy demand, while putting pressure on global water resources. Confronted with severe water shortage, it is imperative to understand its comprehensive impact on water resource. Recently remarkable advances of life cycle assessment and water footprint analysis have been witnessed in this field. Based on a review of the two methods' history, we propose a combination evaluation framework and define an associated indicators set to integrate both methods' advantages. By methods integration, direct and indirect water use are combined with the green, blue, and gray water footprint to describe the water use in detail. Furthermore, the life cycle water footprint of a typical biomass direct-combustion power generation system in China is evaluated based on the combined method. Results show the system life cycle water use is 11.71 L/MJ, while agricultural plantation accounts for the major part (84.61%). In addition, direct green water footprint is the largest component (46.54%), while direct and indirect blue water footprints account for 36.59% and 1.74%, respectively; indirect gray water footprint is 1.771 L/MJ. In terms of water use intensity, the direct-combustion power generation is lower than bio-oil power generation, but far more than solar photovoltaic and wind power. Sensitivity analysis suggests that improving power generation efficiency, straw collection coefficient and cultivating high water-efficient crops can evidently contribute to alleviating water stress conditions for bioenergy production.

Life cycle water use and wastewater discharge of steel production based on material-energy-water flows: A case study in China

Abstract As a water-intensive industry, iron and steel production has caused serious water resource problems in China. This paper first proposes a material flow analysis-input-output model that considers water use factors and system boundaries for a life cycle water analysis. The life cycle water use and wastewater discharge inventories of different products are quantified, and water flow diagrams of life cycle water withdrawal, consumption and discharge for a steel plant in China are graphically mapped. The results show that the total life cycle water withdrawal, water consumption and water discharge per ton of steel in the case plant were 14.93 t, 5.90 t, and 9.23 t. The steelmaking process constituted the largest fraction, while the cold rolling processes constituted the smallest fraction. By analyzing the direct and indirect water and material-energy-water flow, the indirect water usage in energy and material flows was found to be more important to the water flow in the life cycle water use and discharge for steel production, especially for electricity. However, there were many differences among the subprocesses. In coking and sintering, the main factor was material flow; for ironmaking, water flow; for steelmaking, energy and water flows; and for hot rolling and cold rolling, energy flow.

A PRELIMINARY ASSESSMENT OF THE EFFECTS OF DROUGHT ON WATER SUSTAINABILITY INDICATORS FOR NUCLEAR POWER GENERATION IN MONGOLIA

As the effects of climate change are being felt all over the world, sustainability indicators such as water withdrawn per kilowatt-hour, are becoming more important in the decision-making process for large infrastructure projects. In Mongolia, we are deciding whether to use nuclear as a main power source. However, local droughts in Mongolia can be quite severe, occurring every 4-5 years and several countries have shown droughts to interrupt their power plant operations. This study collects data and conducts analyses to estimate sustainability indicators for a nuclear power plant life cycle and extends these analyses to understand how an event such as a drought would affect such indicators. The first part of this study is to provide background information regarding life cycle water use from power generation facilities. Our study focused on the APR-1400 nuclear power plant. If we account for drought frequency in Mongolia, the life cycle water withdrawal is estimated to be approximately 7,611 L/MWh for the nuclear power plant.Keywords: nuclear, sustainability, water, drought

Multi-objective optimization of lignocellulosic feedstock selection for ethanol production in India

Indian biofuel policy targets large scale utilization of lignocellulosic feedstock. Efficient utilization of the available feedstocks without increasing the pressure on the agricultural land, water and other inputs is essential for overall sustainability. This work focuses on recommending the optimal selection of lignocellulosic feedstock for the Indian biofuel sector considering several sustainability indicators. Six different feedstocks, namely, cotton stalk, rice husk, wheat stalk, sorghum stalk, sugarcane bagasse, and sugarcane molasses, are considered for the production of ethanol using a standardized process. The criteria for selection include life cycle greenhouse gas (GHG) emissions, energy return on investment (EROI), life cycle water use, and land use for ethanol production. Since the decision making criteria show trade-offs, multi-objective linear programming problem was formulated. The model targeted a specific amount of ethanol production without exceeding the feedstock availability, and was solved for different ethanol blending targets. The results recommended complete utilization of sugarcane molasses followed by use of feedstocks such as sugarcane bagasse and sorghum stalk. A strong trade-off was observed between GHG footprint and the other two objectives for EROI 5.08 for base case of 20% blending. Optimal feedstock combination included sugarcane molasses (26.8%), sugarcane bagasse (67%), and sorghum stalk (6.2%) for lowest EROI of 5.08. But for highest EROI of 5.6 the optimal feedstock combination included sugarcane molasses (10.2%), sugarcane bagasse (68.3%), sorghum stalk (6.2%) and cotton stalk (15.3%). The scenarios such as reduced availability of sugarcane bagasse, increase in gasoline demand, effect of data variation gives the additional insights for optimal selection of feedstocks for different blending percentages. The work concluded that sugarcane based feedstock were very critical. Moreover, the proposed approach needs to be systematically used by the decision makers for sustainable biofuel development in India.

A simple and objective method to partition evapotranspiration into transpiration and evaporation at eddy-covariance sites

Separating evapotranspiration (ET) into evaporation (E) and transpiration (T) is challenging but key for a better understanding and prediction of the hydrological cycle and plant water use. In this study, flux data at 30 routine eddy-covariance sites were used to develop a new and simple method for ET partitioning based on the separation of soil and canopy conductances, with the main assumption that the latter is proportional to gross primary productivity (GPP). The result of T:ET across different plant functional types (PFTs) was consistent with recent modeling or empirical results. The mean annual T:ET was highest for evergreen needleleaf forests (0.75 ± 0.17), followed by croplands (0.62 ± 0.16) and grasslands (0.56 ± 0.15). The leaf area index (LAI) was shown to explain only small (20%) variations of mean annual T:ET across sites. However, at each site, the correlation of T:ET with LAI was strong at the seasonal scale, where T:ET increased nonlinearly with LAI. The results did not show significant relationship of T:ET with long-term mean precipitation across sites at multiyear timescales. However, the partitioned soil evaporation after each precipitation pulse is consistent with three-stage soil evaporation theory. This ET partitioning method is an objective assessment as it is mainly data-driven. The procedure to apply this method is also simple so it can be readily applied to global flux tower networks at different temporal and spatial scales, enabling continuous estimation of T:ET to monitor ecosystem dynamics and hydrological responses to environmental change.

Assessing life cycle water use and pollution of coal-fired power generation in China using input-output analysis

In the present study, both water depletion and degradation in the life cycle of power generation at coal-fired power plants in China are quantified using a mixed-unit input-output model. National life cycle Withdrawal, Blue and Grey water footprint (WF) of thermal power production in China are estimated to be 35.46, 2.14 and 17.67 m3 per MWh of electricity produced, respectively. Those three types of life cycle WFs experienced significant reductions from 2002 to 2012 due to improved technologies such as water saving and wastewater treatment. Although Chemical Oxygen Demand (COD) pollutant had the largest discharge amount in the life cycle process of electricity generation, petroleum pollutant that was mostly discharged from coal production determined the Grey WF because of its lower permissible concentration. The spatial distribution of scarce WFs, incorporating regional water stresses, is also studied at the provincial level to identify the impacts of thermal power generation on regional water scarcities. Scarce water consumption was concentrated in northern China while scarce water was predominantly withdrawn in eastern China.

Impact of organic waste composition on life cycle energy production, global warming and Water use for treatment by anaerobic digestion followed by composting

In response to significant organic waste generation, environmental policies are increasingly mandating diversion of organic waste from landfills and promoting alternative management practices to produce energy and reduce greenhouse gas emissions (GHG). Anaerobic digestion and composting are organic waste treatment alternatives, however, both practices require careful management to prevent similar environmental impacts as landfills. A model was developed to assess the impact of anaerobic digestion followed by composting of food waste and green waste mixtures on net energy production, global warming potential and scarce water use. The model included the ability to vary the initial organic waste composition, decomposition kinetics and treatment time. Energy needs for composting aeration and water pumping, and water use decreased as anaerobic digestion time increased. Composting water use savings for an organic waste anaerobically digested for 90 days prior to composting compared to zero days prior to composting ranged between 25%–53% for different organic waste compositions (from 1:0 to 0:1 green waste to food waste ratios), and energy use savings for composting aeration and water pumping ranged between 15%–17% and 24%–54%, respectively, for the same conditions. For an anaerobic digestion pretreatment time of 30 days prior to composting, the analysis predicted scarce water use to be 0.31–1.09 m3 swe/Mg waste, primary energy use to be −168.5–298.3 MJ/Mg waste, and global warming potential to be 8.1–26.4 kg CO2e/Mg waste. The results will help inform the design and maintenance of waste treatment in resource-limited environments.