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Background With the increasing concerns on the energy shortage and carbon emission issues worldwide, sustainable energy recovery from thermal processes is consistently attracting extensive attention. Nowadays, a significant amount of usable thermal energy is wasted and not recovered worldwide every year. Meanwhile, discharging the wasted thermal energy often causes environmental hazards. Significant social and ecological impacts will be achieved if waste thermal energy can be effectively harnessed and reused. Hence, this study aims to provide a comprehensive review on the sustainable energy recovery from thermal processes, contributing to achieving energy security, environmental sustainability, and a low-carbon future. Main text To better understand the development of waste thermal energy utilization, this paper reviews the sustainable thermal energy sources and current waste energy recovery technologies, considering both waste heat and cold energy. The main waste heat sources are prime movers, renewable heat energy, and various industrial activities. Different waste heat recovery technologies to produce electricity, heating, and cooling are analyzed based on the types and temperatures of the waste heat sources. The typical purposes for waste heat energy utilization are power generation, spacing cooling, domestic heating, dehumidification, and heat storage. In addition, the performance of different waste heat recovery systems in multigeneration systems is introduced. The cold energy from the liquified natural gas (LNG) regasification process is one of the main waste cold sources. The popular LNG cold energy recovery strategies are power generation, combined cooling and power, air separation, cryogenic CO 2 capture, and cold warehouse. Furthermore, the existing challenges on the waste thermal energy utilization technologies are analyzed. Finally, potential prospects are discussed to provide greater insights for future works on waste thermal energy utilization. Conclusions Novel heat utilization materials and advanced heat recovery cycles are the key factors for the development of waste high-temperature energy utilization. Integrated systems with multiply products show significant application potential in waste thermal energy recovery. In addition, thermal energy storage and transportation are essential for the utilization of harnessed waste heat energy. In contrast, the low recovery rate, low utilization efficiency, and inadequate assessment are the main obstacles for the waste cold energy recovery systems. Highlights Industrial waste heat supply technologies and their exhaust features are reviewed. Waste thermal heat recovery technologies are summarized and reviewed. Thermal cold energy recovery technologies are summarized and reviewed. Challenges and prospects of sustainable energy recovery are analyzed.

The integrated waste energy recovery system (IWERS) is a thermal system that recovers waste heat from steam generated in bakeryovens to produce hot water. This reduces energy and water consumption in shopping centers. This article analyzes the technicalimprovement of incorporating renewable solar thermal energy into the system. It introduces the new solar-powered IWERS(SPIWERS) for the first time. The exergetic efficiency of IWERS and SPIWERS was measured over 1 year in real supermarketslocated in different climatic zones to determine their performance variables. This paper presents precise data for future improve-ments in the energy efficiency of waste heat recovery systems, making it an innovative contribution to the field. The exergeticefficiency of IWERS was found to be lower in subtropical climates, but no significant variation was observed in other climatesstudied. Additionally, the exergetic efficiency of IWERS components decreases with ambient temperature, particularly in warmmonths. Regarding SPIWERS, the highest exergetic efficiency values were obtained in oceanic climates. IWERS employs electricboilers, whereas SPIWERS system utilizes solar collectors. Although IWERS exhibited superior overall exergy efficiency, particu-larly in cold climates, SPIWERS distinguished itself with a reduced environmental impact, wholly supplanting electric power withsolar thermal energy and a swift economic return on investment within a period of less than 4 years, a duration that is half that ofIWERS. A detailed examination of the individual components of each system will facilitate the identification of potential avenuesfor enhancement, ensuring the system’s capacity for adaptation to specific climatic conditions and seasonal variations. Thus, theexergy efficiency of the DWH tank in IWERS remains constant across all climatic zones and throughout the year. This exergyefficiency is approximately 65%. In contrast, a notable variation is observed in the case of SPIWERS, which is more pronounced inmore favorable weather conditions. On the other hand, the exergy efficiency of electric water boilers is greater in colder climatesand times of the year, with a range of 30%–40%. Additionally, the exergy efficiency of the solar collector is greater in months andareas with cool ambient temperatures, optimal solar radiation, and moderate fluid temperatures within the collector, with a rangeof 5%–11%.

The persistent accumulation of plastic waste presents a severe global environmental challenge. This study presents a non-thermal photodegradation and energy-recovery system that selectively cleaves 82 ± 5% of C–C/C–H bonds in polyethene (PE), polypropylene (PP), and polystyrene (PS) within 30 min of UVC (254 nm) exposure. The bond-dissociation energy is harvested via thermoelectric generators (TEGs), delivering 10 W, and via photoelectric cells, yielding 5 W (10 mA.cm- ² at φ < 2 eV), for a combined recovery of 15 W. Emissions are held below 0.5 ppm VOCs and 0.1 mg.m- ³ microplastics. A lab-scale prototype processes 0.5 kg.h-1 of mixed plastic per 0.1 m² reaction area equivalent to 30 Wh.kg-1 of electrical energy and is scalable to 5 kg.h-1 in a pilot module. Real-time FTIR, Raman, and UV-VIS spectroscopy, integrated with an IoT-PID feedback loop, ensures autonomous optimization. Life-cycle assessment indicates a 25% reduction in greenhouse gas emissions compared to conventional recycling methods. A circular-economy framework envisions recovering oligomeric and monomeric fragments for direct reintegration into polymer production. Feature work will implement digital-twin simulations to refine process control, maximize throughput, and ensure long-term system reliability.

Waste energy recovery from mechanical systems represents a promising approach for improving energy utilization in transportation applications. In air brake systems used in heavy-duty vehicles and railway trains, a considerable amount of compressed air is released without being utilized for useful energy conversion. This study presents the design, fabrication, and experimental evaluation of a cost-effective Tesla turbine intended for recovering compressed air energy from such systems. A bladeless Tesla turbine prototype was manufactured using CNC machining and consisted of ten coaxially arranged discs. Two disc materials, aluminum and steel, were investigated in order to examine the influence of material type on turbine performance characteristics. The turbine was integrated into a compressed air system and experimentally tested under inlet pressures ranging from 2 to 10 bar under both no-load and electrical load conditions. The rotational speed of the turbine and the generated electrical parameters, including voltage, current, and electrical power output, were measured and analyzed. The experimental results indicate that increasing inlet pressure leads to a noticeable increase in turbine rotational speed and electrical power output for both disc materials. However, the turbine equipped with steel discs consistently produced higher rotational speeds and greater electrical power output compared with the aluminum configuration under the tested operating conditions. In addition, at lower inlet pressures, the turbine with aluminum discs was unable to generate measurable electrical output, whereas the turbine with steel discs maintained stable operation. Overall, the findings demonstrate the feasibility of using a low-cost Tesla turbine to recover compressed air energy that would otherwise be wasted in air brake systems. The proposed approach may contribute to improved energy utilization in transportation systems where low-pressure compressed air sources are available.

The variable pressure source system is widely used in renewable energy recovery scenarios. However, the instability of the new energy input and the nonlinearity of the power generation system can lead to problems such as more difficult tracking and control of the maximum power point and poor power generation quality. To address the problem of lower efficiency under varying inputs, which is prevalent in renewable energy generation, this paper establishes an energy recovery system model based on power conversion rectifier topology, designs a speed current double closed‐loop control strategy, proposes an online variable‐step maximum efficiency point tracking method based on experience curves, and tests the overall energy recovery effect through system simulation and comparative experiments. The simulation results show that the maximum efficiency point tracking method proposed in this paper reduces the number of optimization searches by 50% and improves optimization speed. The experiment results show that, under the drastic changes of the input, the method proposed in this paper could reduce the total harmonic distortion to 5.65%, improve the energy recovery efficiency by 10.976%, and reduce the fluctuation ratio of the voltage to 2.43%. This study can provide an important reference for the collection and utilization of new energy sources.

Solar collector systems efficiently transform sunlight into energy that may be used to meet various needs. This research aimed to use the Taguchi method to determine the ideal operating parameters for a solar thermal collector with a rectangular spiral absorber. Controllable parameters including mass flow rate, solar radiation, and absorber design were manipulated during the energy recovery process, and features like PV temperature and outlet water temperature were used to assess the system’s effectiveness. The findings indicate that certain criteria significantly affect response indicators. The observed percentage contribution of absorber design, solar radiation, and the mass flow rate was 69.19%, 27.99%, and 2.83% in PV surface temperature. In comparison, the individual percentage contributions were 73.63%, 13.51%, and 10.57% for absorber design, solar radiation and mass flow rate for water output temperatures. The present model’s R 2 values for PV and outlet water temperatures are 97.24% and 99.67%, respectively. The Predictive regression model was found in fine harmony and the maximum percentage error is limited to 0.68%. The maximum analytical electrical efficiency was observed with a spiral rectangular absorber of 14.57% at the lowest mass flow rate of 0.04 kg/s at the lowest radiation level of 600 W/m 2 . In comparison, maximum analytical thermal efficiency was observed with a spiral rectangular thermal absorber of 63.56% at the highest flow rate of 0.06 kg/s and the highest solar radiation level of 1000 W/m 2 . The analytical and experiment findings were in better agreement in this study, with the highest relative error of 7.52%. According to the study’s findings, the rectangular absorber-based PVT system is at its best at a higher mass flow rate to lower PV temperature and boost thermal energy recovery via water. The present research work can be extended for exergy, environmental, and economic feasibility analysis.

Reverse electrodialysis allows for the capture of energy from salinity gradients between salt and fresh waters, but potential applications are currently limited to coastal areas and the need for a large number of membrane pairs. Using salt solutions that could be continuously regenerated with waste heat (>40°C) and conventional technologies would allow much wider applications of salinity-gradient power production. We used reverse electrodialysis ion-exchange membrane stacks in microbial reverse-electrodialysis cells to efficiently capture salinity-gradient energy from ammonium bicarbonate salt solutions. The maximum power density using acetate reached 5.6 watts per square meter of cathode surface area, which was five times that produced without the dialysis stack, and 3.0 ± 0.05 watts per square meter with domestic wastewater. Maximum energy recovery with acetate reached 30 ± 0.5%.

Against the backdrop of the global energy crisis and the urgent pursuit of dual-carbon goals, improving energy efficiency and reducing energy consumption in construction machinery have become central to the industry’s green and low-carbon transition. As key equipment in infrastructure construction, hydraulic excavators generate considerable gravitational potential energy in the boom during cyclic operations. However, the throttling losses inherent in conventional valve-controlled systems not only waste energy but also cause system overheating and reduced efficiency. Owing to its four-quadrant operating capability and high efficiency, the four-quadrant pump-controlled system provides an effective technical platform for recovering boom potential energy. Therefore, this paper presents a comprehensive review of four-quadrant pump-controlled boom energy recovery (FQ-PCBER) systems. First, three representative system architectures—electric, hydraulic, and hybrid—are examined, and their technical characteristics, performance limitations, and applicable scenarios are compared. Subsequently, the review focuses on the control challenges associated with these systems and summarizes advanced control strategies. Finally, practical engineering issues, technical challenges, and future research directions are discussed. This review aims to provide researchers with a clear technical roadmap, accelerate the practical implementation of four-quadrant pump-controlled boom energy recovery technology, and support the green and low-carbon transformation of the construction machinery sector.

This study investigates the performance of dynamic capacitance regulation technology in electric vehicle piezoelectric shock absorbers for energy recovery under varying road conditions. By simulating a quarter-vehicle suspension system, this paper comprehensively analyzes the energy recovery efficiency of piezoelectric shock absorbers on gravel, speed bumps, and bumpy road conditions, comparing the performance differences between traditional fixed capacitance and dynamic capacitance. The results demonstrate that dynamic capacitance regulation technology can automatically adjust the capacitance value in response to instantaneous voltage changes, thereby enhancing energy recovery efficiency under various road conditions. This technology not only improves the energy conversion efficiency of piezoelectric shock absorbers but also strengthens the system’s adaptability to different vibration frequencies and amplitudes. Further simulation evidence confirms that piezoelectric shock absorbers, under dynamic capacitance regulation, achieve better energy recovery performance across diverse road conditions, offering new insights into improving the energy efficiency and sustainability of electric vehicles. The novelty of this research lies in the first application of dynamic capacitance regulation technology to the energy recovery system of electric vehicle piezoelectric shock absorbers, providing a new theoretical foundation and technical reference for optimizing electric vehicle energy recovery systems.

Dry anaerobic bio-conversion (D-AnBioC) of high-solid organic substrates (OS) is considered as a sustainable option for waste management practices in different parts of the world. The basic technology is well implemented, but the improvements are still under way in terms of optimization and pre- and post-treatments of the feed and end-products, respectively. The purpose of this review is mainly to: (1) provide existing knowledge and research advances in D-AnBioC systems to treat high-solid OS; (2) identify major issues involved in bioreactor designing; (3) present factors influencing the bio-conversion efficiency; (4) discuss the microbiology of system operation; (5) provide examples of existing commercial-scale plants; (6) discuss energy and economics requirements. From the detailed literature review, it is clear that the characteristics of OS are the major factors governing the overall process and economics. It shows that not all OS are profitably recycled using D-AnBioC systems. Compared to single-stage continuous systems, batch systems under a multi-stage configuration appears to be economically feasible, however, it must be noted that the available data sets are still inconclusive. Also, limited information is available on green house gas mitigation and restoration of nutrients from the digested residue during post-treatment schemes. A summary at the end presents important research gaps of D-AnBioC system to direct future research.