Energy

Hydrothermal carbonization (HTC) has received much attention in recent years as a process to convert wet organic waste into carbon-rich hydrochar. The process also generates an aqueous phase that is still largely considered a burden. The success of HTC is dependent on finding solutions for the aqueous phase. In the present study, we provide the first investigation of recirculation of the aqueous phase from HTC of poultry litter as a means to concentrate nutrients and its subsequent application to agriculture as a fertilizer. Aqueous-phase recirculation generally resulted in an increase in nitrogen, phosphorus, and potassium concentrations up to cycle 3 with maximum concentrations reaching up to 5400, 397, and 23300 mg L^–1 for N, P, and K, respectively. Recirculation did not adversely affect hydrochar composition or calorific value. The recirculated and nonrecirculated aqueous phases were able to support lettuce growth similar to a commercial fertilizer. Results from this study indicate that the combination of aqueous-phase recirculation and use as a fertilizer could be a suitable method to reutilize the aqueous phase and recycle nutrients back into agriculture, thus increasing HTC efficiency and economic feasibility.

Shower systems, related hot-water systems and pipe losses dominate residential water-related energy. However, many time-based technological, behavioural and environmental factors influence water use and related energy consumption. This has meant that, to date, the performance of these systems has been relatively poorly understood. Here we build on earlier stationary modelling and analysis to develop and apply a Dynamic Water-Related Energy Material Flow Analysis Model in Households (DYNWAREHO). We use this to evaluate a highly monitored household to answer "What are the key energy pathways, their relative importance, and the key factors of influence, in household shower and hot-water supply systems? We explore how significantly hot-water losses can be influenced by showering behaviour and/or technological changes such as pipe insulation. We show that in the household studied, over 85% of the energy used for water heating flows as waste down the drain. Losses are the second largest energy user and account for more than 10% in the studied household. Energy use for actual "showering" accounts for less than 5% of the total. New technologies could influence this significantly. This result clarifies the significant wastage of energy inherent in the design and use of current shower systems. The analysis shows various options designed to improve design and management; it was made possible by the creation of the DYWAREHO model, applicable to any household, and calibrated on a specific Australian household. If acted upon through policy decisions and an appropriate design of shower and wastewater systems, the research can substantially improve the management of water-related energy.

Optimizing water–food–energy (WFE) relations has been widely discussed in recent years as an effective approach for formulating pathways toward sustainable agricultural production and energy supply. However, knowledge regarding the WFE nexus is still largely lacking, particularly beyond the conceptual description. In this study, we combined a grid-based crop model (Python-based Environmental Policy Integrated Climate—PEPIC) with a hydropower scheme based on the Distributed Biosphere Hydrological (DBH) model to investigate the WFE interplays in China concerning irrigated agricultural production and hydropower potential. The PEPIC model was used to estimate crop yields and irrigation water requirements under various irrigated cropland scenarios, while the DBH model was applied to simulate hydrological processes and associated hydropower potential. Four major crops, i.e., maize, rice, soybean, and wheat, were included for the analyses. Results show that irrigation water requirements present high values (average about 400 mm yr⁻¹) in many regions of northern China, where crop yields are much higher on irrigated land than on rainfed land. However, agricultural irrigation has largely reduced hydropower potential up to 50% in some regions due to the substantial withdrawal of water from streams. The Yellow River basin, the Hai River basin, and the Liao River basin were identified as the hotspot regions concerning the WFE interactions and tradeoffs. Further expansion the irrigated cropland would increase the tradeoffs between supporting sustainable food production and conserving hydropower potential in many parts of China. The results provide some insights into the WFE nexus and the information derived is useful for supporting sustainable water management, food production while conserving the potential for hydropower generation in China.

There is increasing interest in using waterbodies as renewable energy sources to heat and cool buildings and infrastructure. Here, we estimate the potentials for heat extraction and disposal for the main lakes and rivers of Switzerland based on acceptable temperature changes in the waterbodies, and compare them to regional demands. In most cases, the potentials considerably exceed the demand, and minor impacts on the thermal regime of the waterbodies are expected. There are, however, critical situations: rivers crossing densely-populated areas, where demand often exceeds the potential, and heat disposal in summer into lowland rivers and shallow lakes, where temperatures may exceed ecological criteria. To assess the impacts of a realistic thermal use, we model the temperature effects in two lakes: Upper Lake Constance, a large lake with relatively low population density, and Lower Lake Zurich, a smaller lake with high regional demand. The estimated mean temperature alterations are −0.05 to +0.02 °C for Lake Constance, and −0.60 to +0.22 °C for Lake Zurich. Based on the model results, we discuss the effects of operating parameters on the efficiency and impacts of thermal use. Our analysis demonstrates that waterbodies provide real alternatives for heat/cold production in many regions of the world.