Hao Chen

Non-thermal plasma-driven advanced oxidation is a promising method for treating organic wastewater, which exhibits rapid reaction kinetics and high pollutant removal and does not need chemical reagents. However, its practical application is often limited by high specific energy consumption and the inefficient mass transfer of short-lived reactive species across the gas–liquid interface. This review summarizes the fundamentals of non-thermal plasma chemistry and the process intensification of plasma multiphase reactors by mass transfer enhancement and waste energy-driven conversion. This review focus on four coupling approaches: microbubble-assisted plasma to expand the reactive interfacial area; plasma coupled with hydraulic cavitation to enhance convection and radical formation; plasma–piezoelectric catalysis coupling to harvest hydraulic energy and promote charge-driven reactions; and plasma-assisted Fenton oxidation to improve the utilization of weakly oxidizing species (H₂O₂). The energy efficiency of various plasma-based oxidation systems is compared and discussed clearly. Key remaining challenges are also discussed, including standardized energy efficiency assessment, scale-up and hydrodynamic control, catalyst stability and fouling, by-product formation and toxicity, and long-term operational reliability. Overall, this review aims to provide guidance for developing efficient plasma-based wastewater treatment systems for large-scale applications.

Bisphenol A (BPA) is an industrial chemical used primarily in the manufacture of polycarbonate plastics and epoxy resins. BPA is considered an endocrine-disrupting chemical (EDC) because it interferes with hormonal systems. Over the decades, several techniques have been proposed for BPA removal in wastewaters. This study discusses recent advancements and progress of effective techniques for BPA removal, including membrane, adsorption, advanced oxidation process (AOPs), and biodegradation. The mechanisms of BPA adsorption on modified adsorbents include pore-filling, hydrophobic interactions, hydrogen bonding, and electrostatic interactions. Among the various agricultural waste adsorbents, Argan nut shell-microporous carbon (ANS@H20–120) exhibited the highest efficiency in removing BPA. Furthermore, the performance of magnetic treatment for activated carbon (AC) regeneration is introduced. According to the present study, researchers should prioritize agricultural waste-based adsorbents such as ACs, highly microporous carbons, nanoparticles, and polymers for the removal of BPA. In particular, the combination of adsorption and AOPs (advanced oxidations) is regarded as an efficient method for BPA removal. A series of relevant studies should be conducted at laboratory, pilot, and industrial scales for optimizing the application of agricultural waste-based AC to reduce BPA or other refractory pollutants from an aqueous environment.

Microalgae-based CO₂ capture has potential as an industrial-scale solution to climate change challenges while also amassing usable microalgae biomass. Computational fluid dynamics (CFD) can optimize CO₂ extraction in microalgae growing systems, especially when paired with phytohormone-regulated growth. This paper examines the use of CFD to predict fluid flow, nutrient distribution, light intensity, and mass transfer in microalgae-based systems, which are crucial for improving photosynthetic efficiency and fixing CO₂. The focus is on how phytohormones, such as auxins and cytokinin, influence microalgal growth and their subsequent involvement in increasing carbon sequestration. Furthermore, this review discusses CFD applications in reactor design, where fluid dynamics and biological kinetics interact to increase biomass yield. The focus on scaling up and transitioning from laboratory to industrial application with the possible integration of computational fluid dynamics with experiment data to enhance simulation precision is addressed. The assessment demonstrates CFD’s potential as an important tool for sustainable CO₂ fixation.

Nuclear energy, as an important component of the power system, has become a key focus of future energy development research. Various equipment and pipelines in nuclear power plants require regular inspection, maintenance, and repair. The pipelines in nuclear power plants are typically large, necessitating a device that can locally isolate sections of the pipeline during maintenance operations. Ice plug freezing technology, an economical and efficient method for maintaining and replacing equipment without shutdown, has been widely applied in nuclear power plants. The structure of the ice plug jacket, a type of low-temperature jacket heat exchanger, affects the flow path of the working fluid within the jacket and consequently impacts heat transfer. This study utilizes Computational Fluid Dynamics (CFD) to establish five types of jacket structures: standard, center-offset (center-in, side-out), helical, helical fin, and labyrinth. The effects of different structures on the freezing characteristics of ice plugs are analyzed and compared. The research indicates that the labyrinth jacket enhances the heat transfer performance between liquid nitrogen and the liquid inside the pipe, forming a larger ice layer at the same liquid nitrogen flow rate. Additionally, the standard jacket has the shortest sealing time at high liquid nitrogen flow rates.

Ice plug technology is an effective method for isolating the pipeline system, which are promising methods utilized in the nuclear, chemical, and power industries. To reduce the cold energy consumption and temperature stress, the multi-stage (1–10) of time-dependent thermal boundary conditions was proposed for the formation of ice plug, while the gradient cooling wall temperature of multi-stage was applied. A numerical model considering the liquid–solid phase change, heat transfer, and time-dependent thermal boundary condition has been established. The effects of the ratio of length and diameter of the cooling wall l_c/d (1–9) on the formation rate and heat flux of ice plug in the pipe has been investigated. The fastest formation rate of ice plug with 800 mm in the axial direction (7.47 cm³/s) was observed in the pipe with the l_c/d of 5. The formation rate of ice plug and the ice formation volume under unit energy consumption VE under various stages (1–10) of cooling wall temperature have been compared. The VE of eight temperature stages (1.45 cm³/kJ) was 1.16 times than the VE of one temperature stage, which satisfied the freezing rate at the same time. This investigation provides insight for proposing an energy-saving system for the formation of ice plug.

The continuous solar collector is a promising heater and reactor for the hydrothermal liquefaction (HTL) of microalgae biomass. To enhance the heat transfer and hydrothermal conversion of microalgae slurry in solar-driven reactors, a static mixer is inserted in the flow channel of the solar collector. A numerical model combining CFD and HTL reactions of microalgae biomass is proposed. Six composition equations of protein, carbohydrates, lipids, biocrude, aqueous phase and biogas were proposed, while corresponding HTL kinetics were utilized to simulate the conversion rate of the reactants and products. The effects of the twist ratio of the static mixer (3–10), flow rate (30–80 L/h) and solar intensity (650, 750, 850 W/m²) on the flow resistance, heat transfer and organics formation of microalgae slurry were investigated. The swirl flow caused by the static mixer with a twist ratio of three increased the convective heat transfer coefficient (97 W·m⁻²·K⁻¹) by 2.06 times, while the production rate of biocrude (0.074 g·L⁻¹·s⁻¹) increased by 2.05 times at 50 L/h and 750 W/m². This investigation gives guidance for utilizing static mixers in solar-driven reactors to optimize the heat transfer and HTL of microalgae biomass with solar heat sources.

Microalgae is a promising metabolism microorganism for the fixation of CO₂ from industrial gas while accumulating microalgae biomass. The process of CO₂ fixation by microalgae is able to be significantly improved by the regulation of phytohormones. However, the complex metabolic mechanism of microalgae regulated by phytohormones and abiotic stress on CO₂ fixation deserves to be explored. To systematically understand the existing status and establish a foundation for promoting the technology, this paper reviews investigations on the metabolic mechanism of microalgae regulated by phytohormones. The influences of nitrogen stress, light intensity stress, heavy metal stress, and salinity stress on CO₂ fixation and lipid production are summarized. In addition, a comprehensive overview of the multistage regulation of phytohormones and abiotic stress on CO₂ fixation and lipid production through microalgae is presented. The recent advances in CO₂ transfer reinforcement and light transmission reinforcement in photobioreactors are discussed. This review provides an insight into the enhancement of CO₂ fixation by microalgae regulated by phytohormones, abiotic stress, and mass transfer in multistage photobioreactors.

Microalgae biomass is an ideal precursor to prepare renewable carbon materials, which has broad application. The bioaccumulation efficiency (lipids, proteins, carbohydrates) and biomass productivity of microalgae are influenced by spectroscopy during the culture process. In this study, a bilayer plate-type photobioreactor was designed to cultivate Chlorella protothecoides with spectral selectivity by nanofluids. Compared to culture without spectral selectivity, the spectral selectivity of Ag/CoSO₄ nanofluids increased microalgae biomass by 5.76%, and the spectral selectivity of CoSO₄ solution increased by 17.14%. In addition, the spectral selectivity of Ag/CoSO₄ nanofluids was more conducive to the accumulation of nutrients (29.46% lipids, 50.66% proteins, and 17.86% carbohydrates) in microalgae. Further cultured chlorella was utilized to prepare bioelectrode materials, it was found that algal based biochar had a good pore structure (micro specific surface area: 1627.5314 m²/g, average pore size: 0.21294 nm). As the current density was 1 A/g, the specific capacitance reached 230 F/g, appearing good electrochemical performance.