Comparative Economic and Life Cycle Analysis of Future Water Supply Mix Scenarios for Hong Kong - A Water Scarce City

Life cycle environmental impacts of urban water systems in China

Urban water systems in China are facing multiple challenges, including rapid urbanisation, climate change and infrastructure ageing. It is crucial to evaluate their environmental performance from a holistic perspective in planning and management processes. To the best of our knowledge, there is a lack of nationwide life cycle assessment (LCA) studies on China's urban water systems that cover all system stages. Therefore, this study aims to present a comprehensive and nationwide LCA analysis that pinpoints the environmental hotspots and their major sources across China. This study was conducted based on water utility databases at the province level, covering water abstraction and treatment, waterwork sludge treatment, water distribution, sewage collection, stormwater drainage, wastewater treatment and sewage sludge treatment. Nine environmental impact categories were calculated and analysed. The results reveal the inequity of environmental impacts across provinces, with overall impacts geographically higher in the east and south, lower in the west and north. However, at the functional unit level, the impacts in the northern and northeastern provinces are higher than other regions. Most environmental categories are dominated by multiple water system stages. The analyses of underlying drivers found that purchased electricity is the primary source of several environmental impacts. This study provides a holistic understanding of the environmental performance of China's urban water systems, offers some insights for comprehensive decision-making support on sustainable water system management, and can also serve as a benchmark for future scenario analysis to explore options for reducing environmental impact.

Life cycle assessment to evaluate the integral water cycle in industrial supply: A real case study

Wastewater recycling technologies are developed in areas where the necessity of water resources cannot be satisfied by natural sources. Nevertheless, nowadays trends and European Union Plans show an increasing interest on using these technologies to reduce environmental impacts. This manuscript aims to address the question of the real environmental results of using these technologies and the differences between each specific case using the Life Cycle Assessment (LCA) methodology. A real case study is analyzed to answer this question: the integral water cycle of a northern of Spain, comparing a traditional water supply system (system I), and an alternative wastewater regeneration plant (system II). System II presents a higher impact for all categories (between 1.2 and 37 times higher), except for land use, where it is reduced by 53 %. These results show a larger impact produced by the alternative system due to higher energy and chemical product consumption. Energy consumption is the main factor causing the highest impact in most of the impact categories for both studied systems, including the one associated to the water resource consumption. It accounts for at least 50 % of the total impact for each system in 7 of the 16 evaluated impact categories. In terms of climate change, energy consumption is not particularly significant in system I, but it is for system II, where it represents around 50 % of that impact. In the categories where the impact is not determined by energy consumption, chemical product consumption and waste and discharge treatment are the most relevant factors. In this sense, this paper highlights the importance of analysing each case specifically and underscores the usefulness of using LCA methodology as a tool to improve decision-making in resource management, with water resources emerging as a crucial focal point.

Environmental impact assessment of multi-source solid waste based on a life cycle assessment, principal component analysis, and random forest algorithm

As a national pilot city for solid waste disposal and resource reuse, Dongguan in Guangdong Province aims to vigorously promote the high-value utilization of solid waste and contribute to the sustainable development of the Greater Bay Area. In this study, life cycle assessment (LCA) coupled with principal component analysis (PCA) and the random forest (RF) algorithm was applied to assess the environmental impact of multi-source solid waste disposal technologies to guide the environmental protection direction. In order to improve the technical efficiency and reduce pollution emissions, some advanced technologies including carbothermal reduction‒oxygen-enriched side blowing, directional depolymerization‒flocculation demulsification, anaerobic digestion and incineration power generation, were applied for treating inorganic waste, organic waste, kitchen waste and household waste in the park. Based on the improved techniques, we proposed a cyclic model for multi-source solid waste disposal. Results of the combined LCA-PCA-RF calculation indicated that the key environmental load type was human toxicity potential (HTP), came from the technical units of carbothermal reduction and oxygen-enriched side blowing. Compared to the improved one, the cyclic model was proved to reduce material and energy inputs by 66%-85% and the pollution emissions by 15%-88%. To sum up, the environmental impact assessment and systematic comparison suggest a cyclic mode for multi-source solid waste treatments in the park, which could be promoted and contributed to the green and low-carbon development of the city.