Sustainable development goals (SDGs) are a comprehensive set of socio-economic and environmental goals, including mitigation measures for climate change impacts targeted by the Paris Agreement. These goals are projected to be achieved by 2030, but this is closely related to long-term climate change countermeasures. The tools used for interdisciplinary evaluation of climate change countermeasures are called integrated assessment models, and the evaluation includes synergies and trade-offs among sustainable development indicators such as energy, water, land use, and economic growth. Since not all sustainable development goals can be solved by engineering alone, an interdisciplinary approach including social science is required. However, in all phases of system design, construction, and operation, chemical engineering as a combination of multiple disciplines in material and energy balance, thermodynamics and system engineering will continue to play an indispensable role in contributing to the achievement of sustainable development goals.

To avoid significant crop quality degradation and yield reduction, it is necessary to establish a suitable solar panel arrangement and control method in an agrivoltaic system. We have developed a model to predict solar radiation on the ground under the solar panels in an agrivoltaic system with rotatable panels. The validity of the model was confirmed by comparison of predictions with the observed solar radiation in a paddy field provided with an agrivoltaic system. The effect of rotation direction of solar panels tracking the sun (east to west or north to south) was then investigated using the model. The results showed that east-west sun tracking control was superior in terms of spatial uniformity of solar radiation under the panels and of power generation, although the total annual solar radiation on the ground was smaller than with the north–south control.

To achieve a decarbonized society and sustainable goals, there is an urgent need to expand the use of industrial unused heat and renewable energy. In order to expand the flexibility of utilization of unused heat, it is necessary to develop a thermal energy storage and transport system that can resolve the spatiotemporal gap between generating unused heat and heat demand. In this study, we focused on the heat storage side in the system and devised a counter-flow type moving bed reactor that stores unused heat continuously. A demonstration test on a scale of about 1/400 of the full scale under actual conditions at a sugar mill was conducted, and a full-scale model was designed by a validated numerical model. In the test, 0.75 kW of continuous heat storage was successfully demonstrated. A numerical model was developed to predict the performance of the heat storage system, and it was found that the test results could be simulated by a steady-state one-dimensional model considering the radial effective thermal conductivity of the packed bed. A full-scale storage system was designed using the validated steady-state one-dimensional numerical model. The design parameters were organized, and a method was established to determine the variable parameters, i.e., packing layer height and inlet gas flow rate, to minimize the auxiliary power required for heat storage at each zeolite flow rate.

In order to construct a metal hydride heat pump system that is active at subzero temperatures, this study aimed to estimate temperature rise from the equilibrium hydrogen pressure. Temperature rise experiments of dry heating and water heating were carried out using a heat-driven metal hydride heat pump. As a result, the characteristics of two types of alloys could be expressed in terms of the exponent of the state quantity ΔP_A and the state change ΔT_B in the heat pump operation before the temperature rise. A prediction formula was created based on the experimental values of the temperature rise from the reaction characteristics of the two storage alloys during the chemical reaction, the change in the hydrogen pressure in the container, and the temperature rise of the alloy. In the water heating experiment, the metal hydride was cooled by putting water around the alloy storage container, and the capacity for storing hydrogen was maintained, so that the calorific value was larger than that in the empty-fired state.

Self-supported porous membranes composed of geopolymer, inorganic polymers with amorphous aluminosilicates were fabricated. Geopolymer paste was prepared by mixing metakaolin, as a aluminosilicate source, with sodium hydroxide or potassium hydroxide and silica gel in water. The paste was then casted on a glass plate and sandwiched with another glass plate to control the thickness of the membrane. The cast geopolymer paste was solidified to form a membrane by the curing process under a controlled temperature oven. The molar ratio of Si, Al, K or Na and the solid/liquid in the geopolymer paste was changed and the self-supported membrane was successfully formed for solid-liquid ratio at 0.5 and the molar ratio of SiO₂ : Al₂O₃ : K₂O=65 : 22.5 : 12.5. The pore size distribution of the geopolymer membrane depended on the curing temperature: the peak of the pore size distribution was observed for 20–30 nm for the membranes cured at 75°C or 100°C, while two peaks at about 20–30 nm and about 9 nm were observed for the membrane cured at 25°C. The gas permeation rate though the geopolymer membranes were inversely proportional to the one-half power of the product of the molecular weight of the permeated gas, the mean pore diameter, and the porosity, suggesting the Knudsen diffusion mechanism is dominant.

Despite its industrial value, sulfur hexafluoride (SF₆) has a high global warming potential of about 24,000, and proper processing is therefore required. In this study, we examined SF₆ decomposition treatment by long DC arc, a new thermal plasma generation method, with addition of steam, H₂, or O₂. The long DC arc was generated between electrodes with a gap of 300 mm at about 5 kW of arc power. Destruction and removal efficiency of 99% or more was obtained with steam and H₂ addition, whereas a maximum of 89% was obtained with O₂ addition. As byproducts, H₂S was generated with excess H₂ addition, and the greenhouse gas SO₂F₂ was generated with insufficient H₂O or O₂ addition. In order to suppress these harmful byproducts, it is desirable to have a strong oxidizing atmosphere and to recover fluorine in the form of HF. Processing with addition of steam at an H/F molar ratio of unity or above was found to be ideal for safe and complete decomposition of SF₆.

Anaerobic ammonium oxidation (anammox) is one of the cost-effective ways to remove nitrogen from wastewater. In fact, full-scale anammox plants have been installed in many kinds of wastewater treatment all over the world. In some types of wastewater treatment systems, there is a possibility to operate anammox processes under high water temperatures due to high temperature of nitrogen wastewater. However, there are few reports on the effects of high temperature conditions on the anammox processes. In the present study, continuous feeding tests using 2 types of anammox carriers were operated under temperature control in the range of 36–38°C. Consequently, nitrogen removal performances were deactivated when water temperature was set to 37°C on the all continuous feeding tests. It was revealed that the ratio of nitrate production (ΔNO₃⁻) against to ammonium removed (ΔNH₄⁺) were decreased when water temperature was increased to 37°C. The ratio of nitrite removed (ΔNO₂⁻) against to ΔNH₄⁺ was also decreased under high temperature inhibition. Microbial community analysis revealed that dominant anammox bacteria in the reactors were Candidatus Kuenenia stuttgartiensis.

High levels of selenium(Se), boron(B), and fluorine(F) are found in wastewaters from coal-fired power plants and glass manufacture, and their efficient removal by simple and inexpensive methods is required. Magnesium oxide (MgO) and ferrous (Fe(II)) hydroxide are used for B and Se(VI), respectively, but their simultaneous removal is difficult because the pH requirements differ. In this study, we examined a wastewater treatment process that can simultaneously remove these elements. MgO and Fe(II) were added to simulated wastewater containing Se(VI), B, F, and SO₄²⁻, and the removal of the toxic elements was evaluated. When 3 g dm⁻³ of MgO and 0.415 g dm⁻³ of Fe(II) were added, concentrations of 1 mg dm⁻³ of Se(VI), 300 mg dm⁻³ of B, and 10 mg dm⁻³ of F could be reduced to below the effluent standard values. Solid analysis of the precipitates showed that the toxic elements were removed in association with hydroxides and layered double hydroxides (LDH) containing Fe(II), Fe(III), and Mg. These hydroxides and LDH were formed around MgO particles, resulting in a large particle size of about 300 µm and a high sedimentation property in suspension. Therefore, this process using MgO and Fe(II) is efficient for removal of Se(VI), B, and F simultaneously and in terms of the sludge treatment.

This study aimed to synthesize ettringite in suspension from various forms of used gypsum and by-product gypsum. We focus on the solubility of the raw material for ettringite. Heat treatment at various temperatures (400–1,000°C) was applied to gypsum and amorphous Al(OH)₃, and the effect of the solubility of Ca²⁺ and Al³⁺ as constituents of ettringite in NaOH solution at pH 12 on the ettringite formation in suspension was investigated using various heated raw materials. The removal of toxic anionic species (B, As(III), Cr(VI), Se(IV)) in dilute solution was tested for the ettringite synthesized under various conditions. By using soluble NaAlO₂ as an Al³⁺ source, ettringite was synthesized successfully after a shorter agitation time of 1 h from CaSO₄·2H₂O and its calcination product at 400°C. For calcination at 600°C and above, ettringite was formed by extending agitation time to 24 h. When amorphous Al(OH)₃ and its calcination products were used as an Al³⁺ source, longer agitation time is required for ettringite formation in suspension. From the viewpoint of ettringite formation, it implies that the solubility of Al³⁺ and the Al³⁺ sources is predominant compared with that of Ca²⁺ from gypsum. It was found that the ettringite as an anion removal agent was synthesized effectively by controlling the reaction conditions to improve the reactivity of Ca²⁺ in gypsum.

Silica scale can cause pipe obstructions in the operation of geothermal power plants, and no effective countermeasure has been established. In this study, we experimentally evaluated the effect of pH (3, 6, 9), temperature (298–353 K), and the presence of metal elements (Mg, Al, and Fe) on silica polymerization and discussed an effective and practical countermeasure against silica scale formation. In our experiments, the behavior of silica and the metal elements varied greatly depending on pH and temperature. At pH 3, no silica polymerization or decrease of the metal elements was observed. At pH 6 and pH 9, however, silica polymerization proceeded. The nucleus growth rate of amorphous silica was lower at pH 6 than at pH 9 and higher in the presence of coexisting elements than in their absence. Furthermore, no induction period was observed in the presence of the metal elements. These results indicated that the metal elements promote the nucleation and growth of silica scale. On the basis of the observed silica scale formation rate, we suggest reducing the residence time (from pumping to re-injection) of hydrothermal fluid under neutral pH conditions in order to suppress silica scale formation, because the nucleus growth rate is relatively low at pH 6. For example, if the geothermal water is re-injected at 353 K, we can confine the decrease of silica concentration to less than 100 ppm by returning the fluid within 4 h.

Perfluorocarbons (PFCs) are used in various industries but require decomposition before they are released into the atmosphere. Many decomposition processes involve hydrolysis of PFCs to produce hydrofluoric acid, which is highly corrosive and leads to rapid deactivation of catalysts. Therefore, we propose the decomposition of CF₄ by a chemical reaction with CaO-enhanced mordenite (MOR) under relatively mild conditions. This study examined, the effects on CF₄ decomposition of the water added when mixing zeolite and a calcium compound and of the inorganic binders used to prepare pellets of the reactant. The reactant comprising CaCO₃ as the calcium compound and attapulgite as the inorganic binder showed equal to or better decomposition of CF₄ compared with MOR/CaO mixed under dry conditions. Due to its low solubility in water, CaCO₃ did not affect the acidity of MOR when water was added. In addition, the fibrous shape of attapulgite improved the diffusivity inside the pellets.

The Dynamix Mixer (WONDER MIX, Nippon Sosey Kogyo Co., Ltd.) has been used in the mixing of two-component curable resins such as two-part mixed adhesives and sealants. Focusing on a performance improvement of the WONDER MIX, several types of elements were newly developed to evaluate mixing performance. As a result thereof, an element structure has been found in which inverse T-shaped unit structures are arranged so as to alternately interlace. This novel element enables mixing at lower rotational speed and with shorter element length compared to existing elements.

HRX300 has high mixing performances and promotes the evaporation by splashing liquid from the free surface. The mixing performance was evaluated by measuring mixing time, power consumption and volume of splashed liquid. The dimensionless mixing time of HRX300 was equivalent to that of Super-Mix MR205 under turbulent flow conditions. The power number of HRX300 was correlated by the same equations as Super-Mix MR205. Furthermore, HRX300 was found to have a high splashing performance at most liquid depths.

A heat exchange system with three heat storage containers filled with phase change materials having different melting points was experimentally investigated to develop a cascaded heat storage system that allows the use of low-level thermal energy in an ambient temperature range. Capric, lauric and myristic acids, which are harmless to the human body, were used as heat storage materials. The heat transport mechanisms involved in the melting and solidification processes were analyzed by means of appropriate visualization and a series of heat transfer experiments.

Dielectric barrier discharge (DBD) plasma treatment of polypropylene (PP) particles using a spouted bed plasma reactor was performed, and the effects of plasma conditions and particle fluidization conditions on the charge of the particle surface were investigated. In the experiment, the plasma conditions such as plasma processing time and applied voltage and the fluidization conditions such as gas flow rate, particle filling amount, and particle size were changed, and the effects of these conditions on the surface charge of PP particles were evaluated. As a result, it was clarified that the spouted bed plasma reactor can add an electric charge to the surface of PP particles. However, the particle surface potential differs greatly depending on the gas flow rate, plasma processing time, and applied voltage, and the gas flow rate has the highest surface potential when the particles are fluidized in the entire reactor. Although the particle surface potential increases as the applied voltage is increased, the surface potential with respect to the applied voltage has a maximum value, and the particle surface potential tends to decrease when a high voltage is applied. It was also found that the surface potential differs depending on the number of loading particles and the particle size, and that the surface potential increases as the number of particles increases and the particle size increases.