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• The maximum treatment capacity of 1167.44 g is achieved in Mode 1 systems. • Optimization of operating conditions enhances energy efficiency and reduces costs. • Systems in Mode 2 exhibit higher energy efficiency but a lower COD removal value. • Switching modes maximize energy utilization across different application scenarios. A multi-stage reverse electrodialysis reactor (MSREDR) wastewater treatment system with an independent strategy is researched theoretically in this paper. The influences of operating conditions on the system performance and levelized costs are explored. Results illustrate that reducing the number of membrane pairs not only enhances the system performance but also decreases the levelized cost of wastewater treatment. A high concentration of concentrated solution facilitates enhancing the total COD removal value and reducing the levelized cost, but it adversely affects the energy conversion efficiency of the system. The optimal total COD removal value and energy efficiency are respectively 1164.77 g and 3.58 % under the given conditions. However, when the wastewater discharge rate from the plant is lower than the maximum treatment capacity, it transitions from a wastewater treatment mode to a combined power generation and wastewater treatment mode. Compared to the system operating in the wastewater treatment mode, the system operating in the combined power generation and wastewater treatment mode exhibits higher effective energy and energy efficiency but a lower COD removal value. This research successfully achieves the flexible adjustment of operating modes based on real-world applications, thereby maximizing energy efficiency and establishing a theoretical foundation for practical implementations. [ABSTRACT FROM AUTHOR]

Wastewater treatment plants (WWTPs) play a pivotal role in natural water recycling and safeguarding the water security of approximately 42% of the world's population, yet they confront challenges posed by escalating energy consumption and regional energy constraints. In this study, we developed an evaluation framework that integrated regional energy scarcity with the operation conditions of WWTPs to quantify their energy efficiencies by applying multiregional input–output (MRIO) analysis and data envelopment analysis (DEA). A case study using this framework was conducted on 3776 WWTPs in 30 provinces in China. The results showed that the average scarcity-based energy efficiency level of WWTPs in China was low, of which those in northern provinces were higher compared to southeastern provinces. Furthermore, only 24 WWTPs in China attained the highest efficiency levels, while the rest had different degrees of input redundancy, indicating an energy-saving potential of 9.05 × 109 kWh. This paper enables the development of optimal efficiency strategies for WWTPs in different provinces considering the potential energy scarcity risks caused by trading activities. • The DEA and MRIO analyses were combined for 3776 WWTPs in China. • Efficiency evaluation index was modified considering energy scarcity levels. • Scarcity-based energy efficiency assessment framework for WWTPs was developed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Feasibility of using organic wastewater as renewable energy source is verified. • ＞99% COD, TOC removal rate in the experimental platform. • Up to 78.75% of the energy recovery efficiency of the SCWO system. The degradation of high concentration organic wastewater and the recovery of energy using supercritical water oxidation (SCWO) technology have the potential to become viable in the future. High concentration organic wastewater contains a significant amount of energy. This paper focuses on utilizing high concentrated wastewater as a renewable energy source, from an energy system perspective, an experimental rig was designed to determine the optimal working conditions. The experiments were conducted with an oxidation coefficient of 1.1, a flow rate of high concentration organic wastewater of 9 ml/min, a heating temperature of 400 °C, and a reaction pressure of 25 MPa. Under these conditions, the COD and TOC removal rates of the high concentration organic wastewater were found to be 99.383 % and 99.876 % respectively. Additionally, the phenomenon of "Abnormalities in pressure sensitivity" observed during high concentration organic wastewater the experiment was further explained through additional experiments. Finally, by comparing the experimental energy recovery with the simulation results, an energy recovery efficiency of 78.95 % was achieved. The feasibility of the simulated energy recovery in practice was verified, confirming the potential to convert the previous energy-consuming wastewater treatment process into a productive one. This study provides a theoretical and experimental foundation for further related research. [ABSTRACT FROM AUTHOR]

This paper focuses on the comparative study of vertical and horizontal vacuum membrane distillation (VMD) modules coupled with mechanical vapor recompression (MVR) system to obtain the optimal system layout structure and further improve operation stability and energy efficiency in the wastewater treatment. Firstly, freshwater accumulation characteristic in the vertical VMD module was explored under different working conditions. Then, comparative experiments of vertical and horizontal VMD-MVR systems were conducted. Finally, comprehensive performance of horizontal VMD-MVR system were evaluated. The obtained results showed that freshwater production in the distilling tank and freshwater accumulation in the VMD module were affected by operation time, feed temperature, feed flow rate, feed concentration and vacuum side pressure. Furthermore, the horizontal VMD-MVR system was proved to be a better choice due to lower freshwater accumulation in the VMD module and energy consumption in comparison to the vertical VMD-MVR system. Finally, long term operation experiment of 240 h indicated evaporation rate dropped to 55 kg/h as operation time reached to 180 h owing to membrane fouling. After membrane cleaning, evaporation rate recovered from 55 to 62 kg/h with a higher recovery efficiency of 95.1 %. Compared to conventional wastewater treatment systems, the horizontal VMD-MVR system exhibited excellent comprehensive performance. [Display omitted] • Performance comparison of vertical and horizontal VMD-MVR were conducted. • Freshwater accumulation in the VMD module affected the evaporation rate. • Vertical VMD-MVR system had higher energy consumption than horizontal system. • Separation efficiency of horizontal VMD-MVR system was 99.9 %. • Evaporation rate recovered from 55 kg/h to 62 kg/h after membrane cleaning. [ABSTRACT FROM AUTHOR]

In response to strong growth in energy intensive wastewater treatment, public agencies and industry began to explore and implement measures to ensure achievement of the targets indicated in the 2020 Climate and Energy Package. However, in the absence of fundamental and globally recognized approach evaluating wastewater treatment plant (WWTP) energy performance, these policies could be economically wasteful. This paper gives an overview of the literature of WWTP energy-use performance and of the state of the art methods for energy benchmarking. The literature review revealed three main benchmarking approaches: normalization, statistical techniques and programming techniques, and advantages and disadvantages were identified for each one. While these methods can be used for comparison, the diagnosis of the energy performance remains an unsolved issue. Besides, a large dataset of WWTP energy consumption data, together with the methods for synthesizing the information, are presented and discussed. It was found that no single key performance indicators (KPIs) used to characterize the energy performance could be used universally. The assessment of a large data sample provided some evidence about the effect of the plant size, dilution factor and flowrate. The technology choice, plant layout and country of location were seen as important elements that contributed to the large variability observed. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to minimise the energy requirement of autothermal thermophilic aerobic digestion (ATAD). To this end, a dynamic ATAD model is presented and assessed. A global sensitivity analysis was performed to identify the operating conditions with the strongest impact on the energy requirements, and thus to choose the most promising optimisation variables. The latter turned out to be the aeration flowrate, the reaction time, and the sludge flowrate. The optimisation problem was formulated following the sequential approach for dynamic optimisation, due to the discontinuous nature of ATAD. The problem was implemented in MATLAB® and solved for two case studies using the eSS algorithm, a global scatter search method that alternates with local algorithms (in our case fmincon) to refine the best solutions. The two selected full-scale case studies include a single-stage and a two-stage system. For the former, a 22% improvement of the energy requirement was achieved after optimisation, and 18% for the latter. Despite its advantages and common use in other fields, optimisation is still relatively rare in wastewater engineering. In the light of the high, rising cost of wastewater treatment, optimisation should become the norm when it comes to design and operation of wastewater treatment plants. [Copyright &y& Elsevier]

Abstract: Several authors have pointed out the need to identify the optimum operating conditions (OCs) of autothermal thermophilic aerobic digestion (ATAD). This study proves the hypothesis that the OCs have the potential to substantially improve the energy efficiency and plant capacity of established ATAD systems. As ATAD is a semi-batch process, its energy efficiency has to be optimized via dynamic optimization (DO). This methodology requires an adequate mathematical model, and appropriate selection of optimization variables. The paper presents an improved mathematical ATAD model based on previous models found in the literature. A global sensitivity analysis (GSA) was performed in order to identify variables with significant influence upon energy efficiency and plant capacity, thus paving the way for the DO of ATAD systems. The results of the GSA show that reactor volume, reactor temperature, and aeration flowrate are significant variables, which is consistent with reported literature. The results of the GSA also show that both energy efficiency and plant capacity of ATAD systems can be substantially improved by altering reactor volume and OCs. [Copyright &y& Elsevier]