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The global potential to obtain clean energy from mixing river water with seawater is considerable. Reverse electrodialysis is a membrane-based technique for direct production of sustainable electricity from controlled mixing of river water and seawater. It has been investigated generally with a focus on obtained power, without taking care of the energy recovery. Optimizing the technology to power output only, would generally give a low energetic efficiency. In the present work, therefore, we emphasized the aspect of energy recovery. No fundamental obstacle exists to achieve an energy recovery of > 80%. This number was obtained with taking into account no more than the energetic losses for ionic transport. Regarding the feasibility, it was assumed to be a necessary but not sufficient condition that these internal losses are limited. The internal losses could be minimized by reducing the intermembrane distance, especially from the compartments filled with the low-conducting river water. It was found that a reduction from 0.5 to 0.2 mm indeed could be beneficial, although not to the expected extent. From an evaluation of the internal losses, it was supposed that besides the compartment thickness, also the geometry of the spacer affects the internal resistance.

Coal is the dominant fuel for electricity generation around the world. This type of electricity generation uses large amounts of water, increasing pressure on water resources. This calls for an in-depth investigation in the water-energy nexus of coal-fired electricity generation. In China, coal-fired power plants play an important role in the energy supply. Here we assessed water consumption of coal-fired power plants (CPPs) in China using four cooling technologies: closed-cycle cooling, once-through cooling, air cooling, and seawater cooling. The results show that water consumption of CPPs was 3.5 km3, accounting for 11% of total industrial water consumption in China. Eighty-four percent of this water consumption was from plants with closed-cycle cooling. China's average water intensity of CPPs was 1.15 l/kWh, while the intensity for closed-cycle cooling was 3-10 times higher than that for other cooling technologies. About 75% of water consumption of CPPs was from regions with absolute or chronic water scarcity. The results imply that the development of CPPs needs to explicitly consider their impacts on regional water resources.

Decades of developments and implementations in the field of high-rate anaerobic wastewater treatment have put the technology at a competitive level. With respect to sustainability and cost-effectiveness, anaerobic treatment has a much better score than many alternatives. Particularly, the energy conservation aspect, i.e. avoiding the loss of energy for destruction of organic matter, while energy is reclaimed from the organic waste constituents in the form of biogas, was an important driver in the development of such systems. Invoked by the present greenhouse alert, the energy involved is nowadays translated into carbon credits, providing another incentive to further implement anaerobic technology. Anaerobic conversion processes, however, offer much more than cost-effective treatment systems. Selective recovery of metals, effective desulphurization, recovery of nutrients, reductive detoxification, and anaerobic oxidation of specific compounds are examples of the potentials of anaerobic treatment. This paper presents a survey on the state of the art of full-scale anaerobic high-rate treatment of industrial wastewaters and highlights current trends in anaerobic developments.

1. Temperature of every channel (including 3-stage water in troughs, circular outer surface, circulating water and ambient); 2. Yield rate; 3. Volume rate of circulating water; 4. Electric conductivity of raw water, etc.

The energy sector is a major source of the anthropogenic CO2 emissions. Therefore, the sector’s de-carbonization is imperative if we intend to curb the progression of Climate Change. Carbon Capture and Storage (CCS) was created in an attempt to reduce the carbon footprint of energy production. Nonetheless, literature shows that water consumption of electricity production nearly doubles when CCS technologies are applied. Those large footprints give an idea of the technology’s impact in the Water-Energy nexus. In this paper we quantify the Water-Energy-Nexus relations for CCS in the EU-28 using a Top-Down system’s approach. We: 1) elaborate the country’s inventory of water availability and consumption, 2) define the system and two indicators to be used, 3) assess specialized literature for quantify those indicators. Results suggest that water availability is not an issue for CCS, but the additional volume in the consumption could create an important impact on the countries’ infrastructure.

Major changes are occurring with far reaching implications for the existing equilibria or disequilibria in the water-energy-food-environment interface. The increased demand of energy worldwide will reflect directly and indirectly on water-dependent systems. Direct implications will come from higher energy prices, which make extraction and conveyance of water more costly. Indirect implications will be in the form of demand for alternative energy sources. It triggers demand for hydropower and remains a major driver¿along with some environmental policies¿for biofuel expansion. The key question is how these effects may alter water allocation and influence food security, rural poverty and environmental sustainability. This paper sets the background and context of this special issue by highlighting some of the major water-related policy issues related to the subject and provides an overview and synthesis of the papers in this special issue. Besides offering insight into how these papers address these questions in the practical context of few selected countries and basins, this paper also indicates some key areas for future research on the subject

Removal of nitrogen compounds in wastewater represents more than 10% of the total electrical demand of the integral water cycle. However, more than 80% of the nitrogen in wastewater comes from urine, where it is highly concentrated in the form of urea (20000 mg L-1). Urea contains a significant amount of hydrogen in its structure which, if recovered, makes urea a potential source of green energy. This thesis demonstrates a novel approach for the energy recovery from urea present in urine at the production source, using decentralised wastewater treatment systems. A new process has been developed in this thesis based on the integration of three steps. In the first step, adsorption is used to recover urea from urea, overcoming the energy limitations of thermal treatments applied to big water volumes. In the second step, thermal treatment is used to desorb the urea, achieving the regeneration of the adsorbent and the production of ammonia. Finally, in the third step, ammonia is used as hydrogen storage molecule to catalytically produce hydrogen on demand. The adsorption of urea is evaluated using activated carbon, determining that urea adsorbs due to physical interactions with i) delocalised π electrons of the pristine surface of the carbon and ii) carboxyl functional groups. The adsorption of urea is reduced when working with real urine due to the presence of organic compounds with affinity for activated carbon that interferes with the adsorption of urea. Thermal treatment of adsorbed urea leads to desorption of urea and regeneration of activated carbon showing a stable urea adsorption capacity during 4 consecutive adsorption/desorption cycles. Simultaneously, ammonia is produced with a 50 – 60 % yield, which is coupled with an ammonia decomposition catalyst to obtain hydrogen. Pilot trials are developed and installed in relevant environments as conventional and waterless urinals, where a social analysis shows a good acceptance towards the solution and pointed some aspects for improving. Energy analysis shows a positive balance due to the combination of the hydrogen produced and the savings in the traditional nitrogen removal. Furthermore, economic analysis indicates that the direct use of ammonia to produce electricity or fertilisers can be a competitive alternative to the obtention of hydrogen.

This work was supported by Ministerio de Economia, Industria y Competitividad, Gobierno de Espana [grant numbers BES-2013-066420, CSO2015-65182-C2-1-P].

The present work focuses on the effects of pressure on the quality of char and primary tar produced from fast pyrolysis of lignocellulosic biomass. Heat treatment has been carried out in a heated strip reactor (HSR) at 1573 K in nitrogen at 2, 4, 8 bar, with holding times of 3 s and heating rate of 104 K/s. The equipment allows quenching the volatiles as soon as they are emitted from the particles and collecting them for further chemical analyses. The char samples are also collected for thermogravimetric analysis in air. The DTG curves in air of char prepared at 2 bar shows two resolved peaks. Increasing the pressure of heat treatment from 2 to 4 bar has a minor effect on char reactivity, whereas further increase to 8 bar drastically changes the char combustion patterns, and the DTG curves exhibit only one well defined peak. For all the process conditions investigated, Oxo-aromatics are the dominant species in the tar. Benzendiol prevails in the 2 bar tar, followed by oxo-aromatic compounds related to lignin structure, while PAHs are mainly present as Fluorene. When pressure increases, Phenols compounds drastically prevail, and PAHs as Anthracene and Pyrene appear.