Mitigating greenhouse gas emissions from municipal wastewater treatment in China.

Municipal wastewater treatment plays an indispensable role in enhancing water quality by eliminating contaminants. While the process is vital, its environmental footprint, especially in terms of greenhouse gas (GHG) emissions, remains underexplored. Here we offer a comprehensive assessment of GHG emissions from wastewater treatment plants (WWTPs) across China. Our analyses reveal an estimated 1.54 (0.92-2.65) × 104 Gg release of GHGs (CO2-eq) in 2020, with a dominant contribution from N2O emissions and electricity consumption. We can foresee a 60-65% reduction potential in GHG emissions with promising advancements in wastewater treatment, such as cutting-edge biological techniques, intelligent wastewater strategies, and a shift towards renewable energy sources.

Global food trade alleviates transgressions of planetary boundaries at the national scale.

Food systems are among the leading causes for transgression of planetary boundaries globally, which define the safe operating space for humanity. We quantify unsustainable environmental impacts of food systems, indicated by the transgression of national-scale planetary boundaries (i.e., the safe operating space for food production in each country), from both production and consumption perspectives of 189 countries/regions around the world. A multi-regional input-output model is used to map the global transfers of the national-scale transgression of planetary boundaries, including freshwater use, land change, and biogeochemical flows (nitrogen and phosphorus). Our results show that China is a major global unsustainable water and nitrogen exporter and an unstable land and phosphorus importer. This means that water and nitrogen uses in China are used to support food demands in other countries, and food consumption in China requires unsustainable land and phosphorus uses elsewhere. In contrast, the US is a major exporter of unsustainable water, land, and nitrogen uses but only an importer of unsustainable phosphorus for food consumption. Globally, compared to a counterfactual scenario where there is no food trade among any countries, food trade saves massive transgressions of planetary boundaries (270 km3 of water, 18 million tons of nitrogen, 7 million tons of phosphorus, and 5,431 million km2 of land). Alleviation of national-scale planetary boundary transgression has been achieved primarily in the US, China, Saudi Arabia, etc., while aggravation was incurred in Pakistan, Australia, Argentina, and so forth.

Too ill to cure? - An uncertainty-based probabilistic model assessment on one of China's most eutrophic lakes.

Eutrophication is a global challenge, which is exemplified by the tremendous efforts but little results in restoring the sixth largest and also one of the most eutrophic freshwater lakes in China, Lake Dianchi. Considering large parametric uncertainties in water quality modeling, the traditionally used deterministic water quality model is expanded to a probabilistic model to explore the Lake Dianchi's potential responses to different levels of pollutant load reductions. The results show that, given the long pollution history and severe pollution state in Lake Dianchi, a minimum pollution load reduction by half (base year 2003) is required to maintain the water quality state as it is now in 40 years. At least a 60% nutrient load reduction is required to generate any likelihood of water quality improvement, however, the system stabilizes quickly after about 10 years, which may explain why tremendous investments have generated little results. 80% of nutrient load reduction for 40 years has 95% probability of meeting the TN target but only a below 50% (45%) probability in meeting the TP target, and even less to meet water quality target for Chla. The feasibility of ever reaching the Chinese drinking water standards for total phosphorous and total nitrogen is questionable.

China's roadmap to plastic waste management and associated economic costs.

Plastic is one commonly used polymer material to support our daily lives. However, once the plastic waste enters the environment, it slowly degrades, which causes long-term and deep ecological environmental problems. As the world's largest plastic producer and consumer, China generated around 26.74 million tons of plastic waste in 2019, and has made ambitious policies to cope with the plastic waste issues. This study predicts the generation trends and management costs of plastic waste in China from 2020 to 2035 under three different scenarios (Business as usual-BAU, Current policy scenario -CPS, and Target policy scenario-TPS), in which China is divided into three regions for specific policy implications. In addition, the scenario analysis and Monte Carlo simulations are used to obtain confidence interval of assessments. The results show that the plastic waste emission will be 34.82 million tons under BAU, 13.49 million tons under CPS and 2.63 million tons under TPS in 2035, respectively, and there will be significant changes in regional contributions in plastic waste emission (e.g., Eastern region: 45.7% to 9.7%; Central region:25.2% to 30.9%; Western region: 29.1% to 59.4% from 2019 to 2035 under TPS). In addition, the environmental and economic benefits increase with the rigor of plastic waste management policy as there will generate a net income of US$3.01 billion under TPS compared to the cost of US$ 2.61 billion under BAU and US$120 million under CPS. In view of this, it is vital that China develop appropriate plastic management policies based on the status of various regions, attempt to achieve economic development while reducing plastic waste emissions, and finally achieving a "win-win" situation of economy and environment.

Unveiling the dynamic of water-electricity conflict within and beyond megacity boundary.

Electricity demand in megacities may exert substantial stress on water resources, which is often expressed through the water scarcity footprint for electricity consumption (WSFE). Conversely, water scarcity may constrain electricity production, leading to increased vulnerability for megacities electricity production. The WSFE and the water related vulnerability of electricity production reflect two aspects of water-electricity conflict. This varies over time by both the amount and location of electricity production. However, no studies have conducted time-series analysis to evaluate the trends of these two indicators, both in terms of severity and spatial characteristics. Our study focused on evaluating trends in water-electricity conflict both within and beyond megacity administrative boundaries. China's four provincial-level megacities, i.e. Beijing, Tianjin, Shanghai and Chongqing, were chosen as case studies. The results show that water related vulnerability of electricity production in Tianjin, Beijing, Shanghai and Chongqing was diverse and can be classified as extreme, severe, moderate and minor, respectively. Between 2006 and 2016, the WSFE of Tianjin experienced an increasing trend, and its water related vulnerability of electricity production remained at the highest level. Beijing's WSFE has decreased, but its water related vulnerability of electricity production has increased. These differing trends highlight the need for joint reductions to both WSFE and water related vulnerability of electricity production in mitigating water-electricity conflict.

Optimizing future electric power sector considering water-carbon policies in the water-scarce North China Grid.

The North China Grid has the highest proportion of fossil fuel-based electricity generation in China and also suffers from severe water scarcity issues. This study uses a multi-objective optimization model to explore future configurations of generating and cooling technologies of the electric power sector in the North China Grid subject to constraints imposed by existing policies on water conservation and carbon reduction in 2030. Our findings highlight that the current carbon reduction commitments of China do not have significant impacts on the North China Grid's electric power sector development while policies in the water sector generate much larger impacts. Imposing water constraint according to the 'Three Red Line' Policy requires increasing utilization of wind power and air cooling systems, which simultaneously increases economic cost and carbon emissions compared to the business as usual scenario. Imposing enhanced carbon emission and water consumption constraints reap the co-benefits of carbon reduction and water conservation by increasing the proportion of solar PV generation to 8.21%, which increases the unit electricity cost from RMB 0.82 per kWh to RMB 1.37 per kWh. In 2030, electricity generation in the North China Grid generates 1599.88 to 1690.89 million tons (Mt) of carbon emissions under different scenarios whereas imposing water constraint reduces water consumption from 3.34 billion m3 to 1.94 billion m3.

Income impacts on household consumption's grey water footprint in China.

Urbanization is accompanied by growing household consumption and changing consumption patterns, with both having impacts on the life-cycle water pollution generated. This study uses the indicator of grey water footprint (GWF) within an Input-Output framework to examine the decadal change from 2002 to 2017 of the life-cycle water pollution change for household consumption in China, where rapid urbanization has particularly posed looming environmental challenges. Against the background of enlarging inequality, the results also shed light on the impacts of households within different income groups. From 2002 to 2017, GWF required by urban household consumption has increased significantly from 1586 to 2195 km3 while that for rural households have decreased slightly from 1139 to 964 km3 during the same period. Total Nitrogen required the largest GWF throughout the whole period and throughout all different income groups. Food consumption dominated the GWF for household consumption. However, the share of GWF for food consumption decreases with income increases, from 83% for extremely poor rural households to 71% for very rich urban households in 2012. Urbanites on average require higher GWF for their consumption than their rural counterparts. An average person from the highest income rural households required 2033 m3 GWF for household consumption, which is higher than a person from a very poor urban household (1685 m3) but lower than that of a person from poor urban household (2149 m3). While household consumption volume increase has been the primary driver for GWF increase, pollution intensity reduction has offset such impacts. Household consumption pattern change's impacts differ by household income and by pollutant considered.

Demographic Scenarios of Future Environmental Footprints of Healthy Diets in China.

Dietary improvement not only benefits human health conditions, but also offers the potential to reduce the human food system's environmental impact. With the world's largest population and people's bourgeoning lifestyle, China's food system is set to impose increasing pressures on the environment. We evaluated the minimum environmental footprints, including carbon footprint (CF), water footprint (WF) and ecological footprint (EF), of China's food systems into 2100. The minimum footprints of healthy eating are informative to policymakers when setting the environmental constraints for food systems. The results demonstrate that the minimum CF, WF and EF all increase in the near future and peak around 2030 to 2035, under different population scenarios. After the peak, population decline and aging result in decreasing trends of all environmental footprints until 2100. Considering age-gender specific nutritional needs, the food demands of teenagers in the 14-17 year group require the largest environmental footprints across the three indicators. Moreover, men's nutritional needs also lead to larger environmental footprints than women's across all age groups. By 2100, the minimum CF, WF and EF associated with China's food systems range from 616 to 899 million tons, 654 to 953 km3 and 6513 to 9500 billion gm2 respectively under different population scenarios. This study builds a bridge between demography and the environmental footprints of diet and demonstrates that the minimum environmental footprints of diet could vary by up to 46% in 2100 under different demographic scenarios. The results suggest to policymakers that setting the environmental constraints of food systems should be integrated with the planning of a future demographic path.

Quantifying urban wastewater treatment sector's greenhouse gas emissions using a hybrid life cycle analysis method - An application on Shenzhen city in China.

Substantial amounts of greenhouse gas (GHG) emissions generated at urban wastewater treatment plants (WWTP) are gaining increasing appreciation. Improving upon the commonly used Process-Based Life-Cycle Analysis (PLCA) and Environmentally-Extended Life-Cycle Analysis (EIO-LCA) models, we construct a Hybrid Life Cycle Analysis (HLCA) model and quantify both direct and indirect GHG emissions at the operational stage of WWTPs in Shenzhen, one of the fastest urbanizing cities in the world. Data are collected from 26 wastewater treatment plants in Shenzhen, out of all 32, covering 5 commonly used wastewater treatment technologies in China, i.e. Sequencing Batch Reactor, Oxidation Ditch, Biological Filter, AAO-MBR and AAO. The results show that WWTPs using AAO-MBR technology have the highest GHG emission intensity, averaging 0.79 tons per m3, primarily due to its large electricity intensity required. WWTPs using other technologies emit 0.27 to 0.39 tons of GHGs per m3 of wastewater treated. GHG emissions associated with electricity use occupy the largest share, ranging from 65 to 75%. Therefore, transforming the energy structure of the electric power sector to low-carbon sources can reduce WWTPs operational GHG emissions. In total, GHG emissions from Shenzhen's urban wastewater sector have increased from below 0.5 million tons in 2012 to over 0.6 million tons in 2017. Inter-model comparison shows that EIO-LCA substantially underestimates the urban wastewater sector's GHG emissions using the water sector's average parameters while PLCA also results in minor underestimations due the omission of indirect emissions in the production stage of chemicals and other material inputs.

Are the Chinese Moving toward a Healthy Diet? Evidence from Macro Data from 1961 to 2017.

The change in diet structure is one of the critical features of social transformation, and diet structure is directly related to human health. In China, with rapid economic development, changes in the diet structure of the population have begun and are proceeding at a fairly rapid rate. In order to reveal how the Chinese diet is approaching or deviating from the nutritional goal, a novel index, NDBI (National Dietary Balance Index), is developed in this study to investigate the Chinese diet from 1961 to 2017 at a national level. The results show that the Chinese diet has transitioned from the under-intake stage to the over-intake stage. Before the 1980s, Chinese people ate all foods inadequately except staple foods; after the 1980s, the issue of under-intake began to fade, and the intake of meats even became excessive. The intake of staple foods is always excessive during this period. Currently, the Chinese diet is still unhealthy because of the inadequate intake of dairy products and the excessive intake of staple foods and meats. By evaluating diet structure on a national level, this study can help people to better understand how the Chinese diet deviated from the nutritional goal and provides information for policymakers intervening in China's food consumption.

Water-carbon trade-off for inter-provincial electricity transmissions in China.

Electricity transmissions have been utilized in China to balance its spatially mismatched development needs and natural resources endowments. However, it has led to spatial shifts of negative environmental impacts induced by electricity generations, including water consumption and carbon emissions. This study calculates that, from 2010 to 2016, carbon emissions and water consumption to produce the transmitted electricity have grown from 507 Mt and 2.7 km3 respectively to 642 Mt and 6.5 km3. Applying a structural decomposition model coupled with a Quasi-Input-Output model to quantify the driving factors of such increases, we find that GDP increase has played the dominant role in driving the increase of both factors. Our results also highlight the potential conflicts between carbon reduction and water conservation in developing future electricity transmission infrastructure systems. Changing the electric power sector's energy portfolio and the transmission structure by increasingly utilizing hydropower productions have both contributed to national total carbon emissions reductions, but at the expenses of increased national water consumption. As a result, on a national level, in 2016, due to the inter-provincial differences in energy portfolios and technologies, electricity transmissions have led to 155.27 Mt of net carbon reduction and 3.4 km³ of additional net water consumption compared to the counterfactual scenario where no electricity transmission were facilitated. The future expansion of electricity transmission network needs to consider such trade-offs, particularly within the contexts of global climate change mitigation and emergent challenges posed by water stresses.

Life-cycle water uses for energy consumption of Chinese households from 2002 to 2015.

China's household energy demands' life-cycle water uses from 2002 to 2015 are quantified with an Input-Output analysis disaggregating rural and urban impacts. 9.73 and 1.60 km3 of water was withdrawn and consumed respectively in the life cycle of Chinese household energy demands in 2015, which was dominated by power and heat uses. An average urbanite's household energy uses, including coal, gas, petroleum products, power and heat, require about four times of life-cycle water uses than its rural counterpart. Among all upstream sectors, while agricultural sectors accounted for the largest shares for all energy uses, oil and gas extraction made significant contributions to petroleum products and gas consumption. A Structural Decomposition Analysis is conducted to disentangle the impacts of four driving factors, i.e. population, demand, economic structure and technology. Population change reduced energy consumption's life-cycle water use for rural households but increased that for urban households. Each economic sector's water intensity decreases, which represent technology advancement, played the dominant role curbing household energy consumption's life-cycle water uses. While power and heat dominates the household energy use profile, urbanization is accompanied by household consumption shifting from coal to gas and petroleum products. In order to reduce household energy consumption's impacts and reliance on water resources, it is imperative to reduce energy production's water use by adopting water-saving technologies, such as air cooling, as well as to reduce upstream sectors' water intensities, such as by promoting drip irrigation.