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Abstract Incorporation of closed wet cooling tower (CWCT) in the existing circulating water system has been recognized as a viable path to reduce water use in process industry. This paper introduces a specifically tailored framework based on model reductions for multiscale optimization of CWCT-based cooling water system considering environmental variations. An optimal design of experiment is performed for accurate approximation of the multivariate probability distributions by generating a finite set of samples over the entire input space. The probability distributions are propagated via multi-sample CFD simulations for constructing the physics-based and data-driven reduced models of CWCTs. Based on the developed reduced models, a multiscale optimization model is proposed for performing integrated design and management of CWCTs and cooling water system. It employs sampling-based stochastic programming and the heterogeneous integration of reduced models of CWCTs and other shortcut models. Finally, the performance of the proposed approach is illustrated through its comparison with a deterministic approach.

Disposal of nitrogen-containing sewage sludge (SS) via gasification leads to the formation of NOx precursors and NOx and ammonia emissions. Pretreatment of SS via hydrothermal carbonization (HTC) was shown to improve coalification, desulfurization, and deamination. In this study, we propose a combined hydrothermal pretreatment and CO2 gasification process for removal of nitrogen from SS and production of energy via the gasification of the pretreated SS. In the HTC process, around 50% of nitrogen contained in the sludge was removed. The derived hydrochar (HC) was subsequently fed for gasification using CO2 as a gasifying agent, which was characterized by the expected reduction in the formation of ammonia. We further improved the process by establishing cogasification of hydrochar with waste leaves. The improvement is believed to be due to the catalytic effect of Ca, present in plant leaves, on the gasification. Cold gas efficiency of the cogasification process of a 1/1 hydrochar/leaves blend by mass was en...

AbstractHow human activities have altered hydrological droughts (streamflow deficits) in China during the past five decades (1961–2016) is investigated using the latest version (v2.0) of PCR‐GLOBWB model at high spatial resolution (~10 km). Although both human activities and climate variability have significant effects on river flows over China, there are large regional north‐south contrasts. Over northern China, human activities generally intensify hydrological droughts. We find that human activities exacerbated drought deficit by about 70–200% from 2004 to 2015. In contrast, droughts over southern China are generally alleviated by human activities. For instance, irrigation and water management (such as reservoir operation and water abstraction) increase drought StDef (standardized drought deficit volume) by about 80% in the Yellow River (north) but reduce it by about 20% in the Yangtze River (south). Human activities slightly reduce drought deficit in the Yangtze River due to the combination of large reservoir storage and low ratio of agriculture consumption to abstracted irrigation water. In contrast, hydrological drought is aggravated in the semiarid Yellow River basin because of high water consumption from agricultural sectors. This study suggests that human activities have contrasting influences on hydrological drought characteristics in the northern (intensification) and southern (mitigation) parts of China. Therefore, it is critical to consider the variable roles of human activities on hydrological drought in China when developing mitigation and adaptation strategies.

Degradation of freshwater ecosystems and the services they provide is a primary cause of increasing water insecurity, raising the need for integrated solutions to freshwater management. While methods for characterizing the multi-faceted challenges of managing freshwater ecosystems abound, they tend to emphasize either social or ecological dimensions and fall short of being truly integrative. This paper suggests that management for sustainability of freshwater systems needs to consider the linkages between human water uses, freshwater ecosystems and governance. We present a conceptualization of freshwater resources as part of an integrated social-ecological system and propose a set of corresponding indicators to monitor freshwater ecosystem health and to highlight priorities for management. We demonstrate an application of this new framework -the Freshwater Health Index (FHI) - in the Dongjiang River Basin in southern China, where stakeholders are addressing multiple and conflicting freshwater demands. By combining empirical and modeled datasets with surveys to gauge stakeholders' preferences and elicit expert information about governance mechanisms, the FHI helps stakeholders understand the status of freshwater ecosystems in their basin, how ecosystems are being manipulated to enhance or decrease water-related services, and how well the existing water resource management regime is equipped to govern these dynamics over time. This framework helps to operationalize a truly integrated approach to water resource management by recognizing the interplay between governance, stakeholders, freshwater ecosystems and the services they provide.

Microwave (MW)-assisted catalytic degradation of organic pollutants draws increasing attention owing to its high efficiency in wastewater treatment. This work developed Cu-loaded biochar (CuBC) catalysts for time-efficient mineralization of refractory and high-concentration oxytetracycline (OTC). With only 1 min at 80 °C, Na2S2O8 achieved 100% total organic carbon (TOC) removal over the Cu5BC, while NaClO mineralized 73.3% TOC over the metal-free BC, in contrast to a relatively low mineralization efficiency (< 35%) achieved by H2O2. The high efficiency in MW-assisted oxidation systems could be ascribed to reactive oxidizing species (•SO4- or •ClO), which otherwise were barely detectable in a conventional heating system. The interactions between CuBC and MW were revealed by correlating the physiochemical characteristics to the MW absorption ability. The proposed catalytic systems can contribute to the development of a high-throughput and low-carbon wastewater treatment technology.

In 2013, the International Association of Hydrological Sciences (IAHS) launched the hydrological decade 2013–2022 with the theme “Panta Rhei: Change in Hydrology and Society”. The decade recognizes the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions. This paper reports on the first Panta Rhei biennium 2013–2015, providing a comprehensive resource that describes the scope and direction of Panta Rhei. We bring together the knowledge of all the Panta Rhei working groups, to summarize the most pressing research questions and how the hydrological community is progressing towards those goals. We draw out interconnections between different strands of research, and reflect on the need to take a global view on hydrology in the current era of human impacts and environmental change. Finally, we look back to the six driving science questions identified at the outset of Panta Rhei, to quantify progress towards those aims.