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Abstract Energy efficiency in water systems contributes significantly towards achieving sustainable water management. Decentralized anaerobic fluidized bed membrane bioreactor (AFMBR) systems with energy recovery have been proposed for greywater recycling in domestic buildings for non-potable uses, such as toilet flushing. This study developed an eco-efficiency analysis (EEA) framework with the integration of life-cycle assessment (LCA) and economic analysis for the evaluation of different water systems. Four water management scenarios including (1) freshwater flushing system, (2) seawater flushing system, (3) greywater flushing system adopting aerobic membrane bioreactor (MBR), and (4) greywater flushing system adopting AFMBR, were analyzed in a case study in Hong Kong. The EEA results reveal the AFMBR greywater reuse scenario to be the most eco-efficient option as the system is capable of energy recovery, recycling of water resource and reduction of sewage treatment loadings. This study has demonstrated that the EEA framework is an effective tool to guide water management towards sustainability and provides a basis for further research on the application of greywater recycling systems on a larger scale.

Due to limited fossil fuel resources, a growing increase in energy demand and the need to maintain positive environmental effects, concentrating solar power (CSP) plant as a promising technology has driven the world to find new sustainable and competitive methods for energy production. The scheduling capability of a CSP plant equipped with thermal energy storage (TES) surpasses a photovoltaic (PV) unit and augments the sustainability of energy system performance. However, restricting CSP plant application compared to a PV plant due to its high investment is a challenging issue. This paper presents a model to assemble a combined heat and power (CHP) with a CSP plant for enhancing heat utilization and reduce the overall cost of the plant, thus, the CSP benefits proved by researches can be implemented more economically. Moreover, the compressed air energy storage (CAES) is used with a CSP-TES-CHP plant in order that the thermoelectric decoupling of the CHP be facilitated. Therefore, the virtual power plant (VPP) created is a suitable design for large power grids, which can trade heat and electricity in response to the market without restraint by thermoelectric constraint. Furthermore, the day-ahead offering strategy of the VPP is modeled as a mixed integer linear programming (MILP) problem with the goal of maximizing the profit in the market. The simulation results prove the efficiency of the proposed model. The proposed VPP has a 2% increase in profit and a maximum 6% increase in the market electricity price per day compared to the system without CAES.

Abstract Improving energy efficiency sustainability is a target of the Chinese government. However, the effectiveness of energy conservation policy is affected by the energy rebound effect under which energy efficiency improvement reduces the effective price of energy services, thereby completely or partially offsetting the energy saved by efficiency improvement. Based on the output distance function, this paper develops an improved estimation model of the energy rebound effect, which is logically consistent with the quantities of energy savings and energy rebounds induced by technological progress. Results show that the aggregate energy rebound effect of 36 industrial sectors in China over 1998–2011 is 88.42%, which implies that most of the expected energy savings are mitigated. Investment-driven economic growth is not conducive to energy-saving and results in a strong energy rebound effect in the following year. The equipment and high-end manufacturing sectors have low levels of rebound effect, indicating that increasing the proportion of such firms in the total manufacturing sector can improve the performance of energy conservation. The high level and heterogeneity in rebound effects strongly suggest that varies strategies are necessary for energy conservation among China’s industrial sectors.

Developing a nexus approach to the quantitative analysis of different environmental sectors including energy, water and carbon emissions is important for promoting integrated sustainable management at a community scale. Universities can be considered small communities in themselves, providing access to data at the community scale, as well as contributing to global sustainability through their education, research and the operation of their own estate. In this study, we developed a conceptual nexus analytical framework based on the combination of different environmental footprints to assess how universities, as an example of a small community, interact with the hydrological cycle, energy resources and climate, through their operations and food procurement. Using Keele University in the United Kingdom as an example, the total energy footprint, carbon footprint and water footprint in the 2015/16 academic year was 42,202 MWh, 14,393 tonnes of CO2e and 532,415 m3. Through the quantification of these interlinked environmental footprints, the nexus across water, energy, waste disposal, food procurement, and corresponding carbon emissions at Keele University have been explored. Based on the results of the nexus analysis and identifying the areas of greatest environmental benefit studied, policy suggestions are provided including: implementing energy control systems; maximising the development of wind energy and solar photovoltaic; increasing the availability of vegetable-based options in food procurement decisions; and collecting all of the food waste for anaerobic digestion. The findings serve as a reference for policy-makers and practitioners making decisions on the basis of sustainability in universities and other communities.

Abstract As a major GHG emissions source with large growth potential, the passenger transport sector plays a crucial role in deep decarbonization in China. Large disparities among provinces in private vehicle ownership, sufficiency of public transport infrastructure, affordability of clean fuel vehicles, etc. highlight the importance of regionally tailored mitigation strategies to fully exploit carbon reduction potentials. We classify 31 provinces in mainland China into three regional clusters based on their passenger transport development level, then establish a provincial level bottom-up model to project energy demand and CO2 emissions of China’s passenger transport sector by 2050. Mitigation effects of improving vehicle energy efficiency, shifting to alternative clean fuels, and promoting public transport are compared, and regionally tailored policy priorities are then proposed. The results show that CO2 emissions of China's passenger transport sector will peak around 2045 at 647 MtCO2 and slightly declined to 642 MtCO2 in 2050 in the Current Policies Scenario. If fully implemented, regionally tailor mitigation strategies that maximize techno-economic carbon reduction potentials could cut CO2 emissions substantially to net-zero in 2050. Mitigation effects of different policy options vary among time periods and regions. Improving vehicle fuel efficiency contributes the most in carbon mitigation over short time scales especially in less developed provinces, where private vehicle ownerships are projected to increase rapidly. Well-established transport infrastructure and an optimally designed public transport system could play a larger role in wealthier provinces.

Inner Mongolia Autonomous Region (IMAR) is one of China's strategic energy bases for the 21st century. While bioenergy in IMAR may play an important role in securing future energy supply, little research has been done so far, particularly for crop stalk resources as a potential source of bioenergy in this region. In this study we systematically analyzed the temporal and spatial patterns of crop stalk resources, evaluated the bioenergy potential of crop stalk resources, and explored possible pathways of developing stalk-based energy strategies in Inner Mongolia. Our results show that the total crop stalk yield in IMAR increased consistently from 1980 to 2008, with an average annual increase of 16.3%. Between 2004 and 2008, 26.14 million tons of crop stalks were produced each year in IMAR, 8.82 million tons of which could be used for biofuel production. Grain crops contributed most to the total amount of stalks for energy produc- tion, of which corn stalks were the largest contributor, accounting for 62% of the total crop stalk yield. Based on the current trend, crop stalk yields may continue to increase in the future. Geographically, the abundance of biofuelable crop stalk resources, either on a per capita or per unit of area basis, had a spatial pattern of ''high on East and West and low in the middle''. Our findings suggest that IMAR has the potential for developing stalk-based bioenergy to improve its current overwhelmingly coal-dom- inated energy structure. However, more detailed and comprehensive studies are needed to figure out how exactly such bioenergy development should be carried out in a way that would promote the regional sustainability of Inner Mongolia - i.e., simultaneously providing social, economic, and ecological benefits.

Abstract In wastewater treatment plants (WWTPs), the majority of energy inputs is consumed by aeration systems to support both the biochemical oxidation of organics and transformation of ammonia-nitrogen into nitrate-nitrogen. Consequently, WWTPs energy efficiency evaluation only based on metrics derived from the organic constituents such as chemical oxygen demand (COD) or biological oxygen demand (BOD) may not reflect the true energy consumption of WWTPs with variable influent quality. Therefore, to overcome this limitation, total oxygen demand (TOD) is introduced in this article, and a novel index EO, namely the energy consumption for the removal of a unit mass of TOD is proposed for evaluating the energy efficiency in WWTPs. Furthermore, by considering the stoichiometric relations of oxygen consumption for the oxidation of both organics and ammonia-nitrogen, methods for calculating the EO are proposed. Using the novel EO index and the available annual operation data of 2022 WWTPs, the current status of energy consumption for wastewater treatment in China were analyzed. The findings show an average EO decrease from 5.2 kWh/kg to 1.2 kWh/kg as the WWTP loading rates increase from 20% to 100%. Also, EO decreased from 4.1 kWh/kg to 1.5 kWh/kg as the average TOD removal increased from 60% to over 90%. Moreover, EO decreased from 2.9 kWh/kg to 1.0 kWh/kg as the WWTP scale increased from less than 10,000 m3/d to over 5,00,000 m3/d. Thus, the energy efficiency of WWTPs increases with increasing loading rates, TOD removal, and scale. Also, the wastewater treatment technology applied influences the EO significantly, especially for small- and medium-size WWTPs with capacities less than 50,000 m3/d which account for circa 76% of all WWTPs in China. The WWTPs applying sequential batch tractors (SBR) tended to show lower average EO (

Abstract This study analysed the sustainability of fuel-ethyl levulinate (EL) production along with furfural, as a by-product, from cornstalk in China. A life cycle assessment (LCA) was conducted using the SimaPro software to evaluate the energy consumption (EC), greenhouse gas (GHG) and criteria emissions, from cornstalk growth to EL utilisation. The total life cycle EC was found to be 4.54 MJ/MJ EL, of which 94.7% was biomass energy. EC in the EL production stage was the highest, accounting for 96.8% of total EC. Fossil EC in this stage was estimated to be 0.095 MJ/MJ, which also represents the highest fossil EC throughout the life cycle (39.5% of the total). The ratio of biomass to fossil EC over the life cycle was 17.9, indicating good utilisation of renewable energy in cornstalk-based EL production. The net life cycle GHG emissions were 96.6 g CO 2 -eq/MJ. The EL production stage demonstrated the highest GHG emissions, representing 53.4% of the total positive amount. Criteria emissions of carbon monoxide (CO) and particulates ⩽10 μm (PM10) showed negative values, of −3.15 and −0.72 g/MJ, respectively. Nitrogen oxides (NO x ) and sulphur dioxide (SO 2 ) emissions showed positive values of 0.33 and 0.28 g/MJ, respectively, mainly arising from the EL production stage. According to the sensitivity analysis, increasing or removing the cornstalk revenue in the LCA leads to an increase or decrease in the EC and environmental emissions while burning cornstalk directly in the field results in large increases in emissions of NMVOC, CO, NO x and PM10 but decreases in fossil EC, and SO 2 and GHG emissions.