Outstanding Paper Award Subcommittee of Kagaku Kogaku Ronbunshu has assessed the 31 papers published in volume 42 in 2016, and the editorial board finally selected the two papers for Kagaku Kogaku Ronbunshu Outstanding Paper of 2016; these are the papers on “Thermo-Physical Properties of Phase-Change Latent Heat Storage Material Fatty Acid and Heat Transfer of Natural Convection in a Horizontal Enclosed Rectangular Container” and “Characteristics of NO Formation on Premixed Flame with Microwave Superposition.”

Knowledge of climate change research has influenced international politics. The Kyoto Protocol in the United Nations Framework Convention on Climate Change obliges developed economic parties to reduce greenhouse gas emissions, while the Paris Agreement requests all parties to join the reduction framework. Climate change countermeasure technology is categorized into mitigation, adaptation, and climate engineering. Research organizations internationally have analyzed mitigation scenarios such as new energy technology feasibility and greenhouse gas emission pathways utilizing integrated assessment models. An inventory of model results contributed meta-analyses in the fifth assessment reports of the intergovernmental panel on climate change. Consideration of the energy system should include viewpoints of both supply and demand. For example, the net zero energy building is proposed as a new concept in which net annual energy consumption of a building is almost zero; and this could lead to zero emission in the building sector in combination with low CO₂ energy carriers. Summation of nationally determined contribution greenhouse gas emission numbers would not reach the level required to achieve the long-term temperature rise target adopted in the Paris Agreement. Some scientists consider climate engineering, namely, human intervention in the climate, as an option. CO₂ removal and solar radiation management are the options of climate engineering, and practical evaluations are under way in the area of climate-energy system modeling and social sciences. Chemical engineering-related research, development and deployment will play an important role in almost all fields of technological climate change countermeasures in the future.

Wit the increased production of plastic products worldwide, plastic recycling technology has assumed increasing importance in recent years from the standpoints of efficient use of resources and energy saving. This paper focuses on the role of feedstock recycling within the plastic recycling sector. One benefit of feedstock recycling is that it allows the collection of high concentrations of monomers, which can be used again as raw fuel. Feedstock recycling also involves techniques that use generated gas and residue. This paper chiefly discusses new technological trends and the problems in feedstock recycling. The current state of plastic recycling research and technology development are also examined from an international perspective. Results revealed an increase in technical problems associated with plastic recycling due to the increasing complexity of industrial and household plastic waste composition. On the other hand, further challenges with feedstock recycling were found to be rooted in policy and social systems, although results varied across the different countries that were analyzed.

To clarify of the adsorption behavior of arsenic ions in alkaline solutions, we conducted arsenic adsorption tests for conventional adsorbents (polymer resin adsorbents and inorganic ion-exchangers). For polymer resin adsorbent, the adsorbent with glucamine groups adsorbed trivalent arsenic ions via hydroxyl groups in glucamine, and the strong base ion-exchanger adsorbed pentavalent arsenic ions through anion exchange. For inorganic ion-exchangers, hydroxides and iron hydroxide oxides had high ability to adsorb trivalent and pentavalent arsenic ions, and the adsorbability of hydroxides and iron hydroxide oxides for trivalent arsenic ion was higher than that for pentavalent arsenic ion. In particular, cerium(IV) hydroxide was found to be an excellent adsorbent for trivalent and pentavalent arsenic ions in alkaline solutions.

Removal of arsenite (As(III)) and arsenate (As(V)) from aqueous solution by Fe–Al composite oxides as adsorbents was investigated. Fe–Al composite oxides were synthesized by calcination of precursors containing Fe³⁺ and Al³⁺ hydroxides prepared by co-precipitation. Various composite oxides were prepared, and the effects of pH and the ratio of Fe and Al on the removal of arsenic, and the simultaneous removal of As(III) and As(V) from solution were investigated. Composite oxides calcined below 500°C were found to be typically amorphous, and the results of specific surface area and As removal indicated that calcination at 300°C was appropriate. At a molar ratio of Fe : Al=1 : 1, both As(III) and As(V) were effectively removed. In particular, As(V) removal was drastically improved by the synergistic effect of complex of Fe³⁺ and Al³⁺. The adsorption isotherms of As(III) and As(V) were of Freundlich type and Langmuir type, respectively. Simultaneous removal tests at different As(III)/As(V) ratios showed that the composite oxide synthesized at Fe : Al=1 : 1 and 300°C had excellent removal ability.

Hydrogels based on copolymers of N-[3-(dimethylamino)propyl] acrylamide (DMAPAA) and N,N′-methylenebis(acryl amide) (MBAA) were prepared as media for selective metal ion removal. Polymerization mixtures were polymerized to create cylindrical shapes of 6 mm in diameter. The hydrogels were protonated when they were swollen in water and exhibited higher pH internally than the surrounding water because of ionic interaction. The pH of the hydrogel could be controlled by the adjusting the preparation conditions such as the centration of monomer or crosslinker. Metal ion removal experiments were carried out by swelling the hydrogels in aqueous solutions of metal ions. The metal ions diffused into the hydrogels to produce metal hydroxide in the hydrogel. The hydrogels containing metal hydroxides were easily separated from the solution without controlling the pH of solution or the sedimentation process. The amount of metal removed in the hydrogel increased with the concentration of the metal ions in solution. A target metal ion could be selectively removed from mixed metal ion solutions by controlling the pH of the hydrogel. The metal hydroxide with lower solubility product was preferentially removed by the hydrogel. Hydrogel containing metal hydroxide could be regenerated repeatedly by immersion in aqueous sodium hydroxide solution. These results suggest the possibility of replacing the coagulation and/or adsorption methods of metal ion removal with a novel method with a simple and low emission process.

Some of the many kinds of sulfide ore previously produced in Japan have generated acid mine drainage (AMD) by exposure to oxygen in groundwater or air after closure of the mines. AMD is typically treated by neutralization with lime (Ca(OH)₂) or calcium carbonate (CaCO₃). This process can remove many toxic elements from the AMD in a simple way, but the amount of neutralizer used is often decided based on experience because the removal mechanism of each element has not been quantified. Seasonal variation in the quality and quantity of AMD is considerable, and for many mines their AMD needs to be treated semi-permanently. Thus, more efficient and stable treatment is required in order to reduce chemical input and sludge generation.

With a view to construction of a more efficient AMD treatment method and process, this study aims to develop a simulator that can represent water quality. To this end, a quantitative model that can represent changes in pH and the concentration of each element was constructed using a chemical equilibrium calculation that incorporates surface complexation by ferrihydrite and aluminum hydroxide, which have the potential to remove many kinds of toxic elements. For the surface complexation model of each hydroxide, the double layer model was used. By comparing the calculated results with experimental results obtained from neutralization of two kinds of actual AMD, it was confirmed that the quantitative model constructed in this study could successfully represent the changes in pH and residual concentration of each element.

The recent dramatic increase in demand lithium ion batteries (LIBs) in the automotive and electronic industries makes it desirable to establish sustainable recycling technology to recover cobalt from the cathode material (LiCoO₂). Although the combination of physical and hydrometallurgical processes is one option for recovery of metals, the large amount of aluminum in the cathode of spent LIBs can negatively affect the process performances. Therefore, as a means to enhance the cobalt recovery from spent LIBs, we investigated the feasibility of a physical process for separation of cobalt and aluminum by thermal treatment and wet magnetic separation. Results highlighted the efficiency of the thermal treatment for conversion of the cathode material to magnetic cobalt due to (i) the presence of the more reactive lithium-deficient Li_xCoO₂ (x<1), (ii) the presence of reductive aluminum and graphite from electrode supports, and (iii) the generation of CO, CH₄ and C₂H₄, which activate reduction and carbonation. Furthermore, a slow rise in temperature during heating promoted increases of the grain size of CoO and Co and prevented the pulverization of Al. As a result, 75.5% of cobalt could be recovered from spent LIBs without contamination by aluminum.

Use of chars produced by carbonization of biomass (cypress chips) as molecular sieving carbon was examined. The possibility of separating binary mixtures of gases (CO₂–CH₄ and C₃H₈–C₃H₆) was investigated by measuring the amounts and rates of adsorption on the chars. With the CO₂–CH₄ mixture, both gases were adsorbed, and CO₂ was adsorbed in greater amount than CH₄. On the char prepared by carbonization at above 800°C, the adsorption rate of CO₂ was 30–180 times faster than that of CH₄. With the C₃H₈–C₃H₆ mixture, only C₃H₆ was adsorbed on the char produced at 800–900°C. On the char produced at 700°C, the adsorption rate of C₃H₆ was 110 times faster than that of C₃H₈. Thus, it was concluded that the cypress char can be used for gas separation.

The dry-thermophilic anaerobic digestibility of alternative biomasses to rice straw for pig manure treatment was evaluated. Seven grass and three woody biomasses were subjected to batch dry-thermophilic anaerobic digestion for methane (CH₄) production. The CH₄ production potential ranged from 109±8.1 to 347±62 m³/t-VS, with woody biomasses showing the lowest potential. This trend indicates a negative correlation between lignin content and CH₄ production potential, suggesting that lignin content determines the CH₄ production of the grass and woody biomasses. CH₄ production quantities in Ibaraki Prefecture, where pig farming has been intensively practiced, were estimated to be respectively 31.3, 1.68, and 1.42 m³/y from rice straw, riverbed grasses, and wood (from riverbeds, parks, roads, and orchards). CH₄ production yields from semi-batch dry-thermophilic anaerobic digestion of pig manure with cogon grass (Imperata cylindrica) and wood chips were respectively 251±44 and 157±9.4 m³/t-VS. These values were comparable to the CH₄ production potential of these biomasses, suggesting their promise as alternatives to rice straw.

With a view to establishing a methodology for using the heat from aerobic fermentation of woody biomass as a heat source for greenhouses, the influence of temperature, water content and C/N ratio on the fermentation rate of larch shavings was investigated using a laboratory-scale fermentation apparatus. Larch shavings were mixed with fermented chicken manure, which was utilized to alter a C/N ratio of the mixture, and further mixed with a microorganism source. A 2-L aluminum fermenter loaded with the mixture was maintained at a constant temperature with forced aeration. Oxygen concentration was continuously monitored at the inlet and outlet of the fermenter, and the fermentation rate was evaluated as the oxygen consumption rate estimated from the difference in the measured oxygen concentrations. The results showed the highest oxygen consumption rate was obtained at 40°C and 60% of water content (wet mass basis) at a C/N ratio of 70. Experiments at C/N ratios of 13, 20 and 70 showed that the oxygen consumption rate per unit mass of the mixture did not always increase with decreasing C/N ratio, while the oxygen consumption rate per unit mass of larch increased. This was because the nitrogen content of the fermented chicken manure was small, and a large amount of the chicken manure needed to be added to reduce the C/N ratio. Analysis of the gas discharged from the fermenter showed that almost all the oxygen consumed in the fermenter was converted to carbon dioxide, which indicated that fermentation took place under aerobic conditions. Finally, the mass and volume of the fermentation materials required for heating were estimated.

Experiments were conducted to elucidate the auxiliary effect of adding fibrous materials recovered from a primary settling tank on dewatering digested sludge. Experiments with a constant-pressure filtration device revealed that addition of the fibrous materials increased the filtration rate and decreased the average specific filtration resistance. This improvement in filterability increased with the increase in the amount of the fibrous materials added. Experiments with a full-scale screw press for dewatering demonstrated a decrease in the water content of the dewatered cake from 82 to 68% on addition of the fibrous materials. The correlation between the increase in the proportion of fibrous material added and the decrease in water content of the dewatered cake could be rationally described by a quadratic equation, indicating that the water content of dewatered cake can be controlled by adjusting the proportion of fibrous materials added. Furthermore, the addition of the fibrous materials to digested sludge increased the speed of treatment and decreased the amount of polymer coagulant required. These findings indicate that fibrous materials recovered from a primary settling tank are promising auxiliary agents to improve the dewatering of digested sludge.

Seaweed bed depletion in coastal areas resulting in “barren ground” is a serious problem in Japan and around the world. Focusing on the lack of dissolved iron as one of the possible factors causing barren ground, we have developed a method for restoring seaweed beds using steelmaking slag and compost containing humic substances. This method is useful for effective utilization of a byproduct and unused biomass for improvement of the coastal environment. Its effectiveness has been confirmed in a field test in the Sea of Japan in Hokkaido, and fundamental studies have been conducted for practical use. In the previous works, the effect of organic matter on the acceleration of iron elution from steelmaking slag was investigated through iron elution tests using steelmaking slag, compost, and bamboo. In this study, we evaluated the effect of organic matter through an iron elution test with nine samples consisting of steelmaking slag, compost, bamboo charcoal, and magnesium ammonium phosphate (MAP) supported on bamboo charcoal. We also evaluated the characteristics of phosphorus elution from the samples. It was found that mixing steelmaking slag with organic matter was effective for accelerating iron elution, and the amount of organic matter eluted and its structural characteristics were important for utilizing this method. We also confirmed the elution of phosphorus from the fertilizer. However, this method was expected to be useful for iron fertilizer rather than phosphorus fertilizer.

Chelating agents were used to accelerate the photodegradation of perfluorooctanoic acid (PFOA) catalyzed by Fe³⁺. Citrate, oxalate, and EDTA as chelating groups each accelerated the catalytic photodegradation to a similar degree. The dissolved iron concentration in the Fe-citrate system with equimolar amounts of citrate and Fe³⁺ was about 1.8 times higher than that in the absence of chelating agent, indicating that the higher concentration of dissolved iron was a factor in the acceleration. Since about 70% of the added Fe³⁺ remained in solution in the Fe-citrate system, use of a higher molar ratio of citrate did not result in further acceleration of the PFOA photodegradation. As for the mass balance of fluorine, the use of Fe³⁺ in combination with citrate resulted in much more defluorination of the PFOA molecules and the resultant perfluoro intermediates. The acceleration resulting from the combined use of Fe³⁺ and citrate was diminished by increase of the UV light power from 14 to 40 W.

To investigate the environmental dynamics of radioactive cesium (Cs) and strontium (Sr) in farmland in Japan, non-radioactive Cs and Sr were added to field plots and their absorption by pasture crops was examined. The intrinsic Cs absorption capacity of plants was also examined by cultivating them in agar to exclude the possibility of Cs adhering to soil particles. In the field experiment, crop yields decreased when Cs and Sr were added together but did not change significantly when Cs or Sr alone was added. Addition of Cs to the field plot resulted in significantly higher Cs concentration in the crop, while addition of Sr had no such effect. The amount of Cs accumulated by the crop, however, was less than 1% of the amount added to the plot, suggesting that only a limited amount of radioactive Cs from fallout would be translocated to the crop. The agar cultivation test revealed a positive correlation between the growth rate and the Cs content of the crop. The Cs concentration in plants cultivated in agar was closely correlated with that in the field crop. This suggested that Cs absorbed by plants in farmland remained in a free state because K and Ca in soil inhibited its adhesion to soil particles. In conclusion, it was considered that almost all Cs in farmland adhered to soil particles and was not available for adsorption by plants, while a small portion remained in a free, absorbable state due to the effects of nutrient elements.

Discharge of chemical compounds in pharmaceuticals and personal care products (PPCPs) without appropriate treatment is an environmental problem. Ammonia-oxidizing bacteria (AOB) oxidize ammonia to nitrite and have also been reported to degrade recalcitrant organic compounds by co-metabolism. In this study, Nitrosomonas europaea, a typical ammonia-oxidizing bacterium, was tested against the antibiotic clarithromycin (CAM) and the anticonvulsant carbamazepine (CBZ) and was found to degrade CAM but not CBZ. The pseudo-first-order degradation rate constant of N. europaea for CAM was at maximum one order of magnitude higher than that of activated sludge, showing the feasibility of biodegredation of CAM by N. europaea. Respirometric assay indicated that N. europaea was inhibited at a CAM concentration above 10 µg/L. The microarray for gene expression demonstrated the presence of upregulated genes for ammonia oxidation and ribosome synthesis.

In a fluidized catalyst bed, defluidization occurs when the fluidizing gas is switched from lower to higher density gases. This phenomenon occurs when the gas velocity in the emulsion phase falls below the minimum fluidizing velocity due to non-equimolar counter diffusion between the emulsion phase and the bubble phase. Non-equimolar diffusion in small pores under isobaric condition is known as Graham’s law, and many models have been proposed since the mid-20-century. In these models, non-equimolar counter diffusion is explained using the binary diffusion coefficient, because the phenomenon occurs in the molecular diffusion region. In this study, equimolar counter diffusion is not assumed when the pore size is small even in the molecular diffusion region; rather, according to the recognized mechanism of equimolar diffusion, it is explained by the intrinsic diffusion of each molecule and the flow caused by the pressure gradient. To confirm this explanation, a model was proposed that includes an equation for the intrinsic diffusion coefficient. Calculations based on this model showed good agreement with previously reported experimental data on the binary gas diffusion in pores under isobaric or isovolumetric conditions.

In order to evaluate aerosol penetrations through a fully developed laminar flow in a cylindrical tube, the trajectories of aerosol particles were calculated by a Langevin dynamics equation that can represent the Brownian motion of aerosol particles. In our calculations, two criteria of penetration distance were employed: the maximum distance that a particle travels in the axial direction before it is deposited on inner wall of the tube, z_MTD; and the axial distance from the inlet of tube to the point of deposition, z_DD. The distributions of these two penetration distances enable us to evaluate respectively the classical penetration, defined as the ratio of total particle flux over a cross section of tube to the total particle flux at tube inlet, and the distribution of deposition flux to the tube wall. At high Péclet numbers of Pe>1000, there is almost no difference between z_MTD and z_DD. The resulting penetrations calculated from the distribution of z_MTD agree well with the conventional analytical solution of convective-diffusion of aerosols in which the diffusion of aerosol particles in the direction of flow is neglected. At low Péclet numbers of Pe<1000, the isotropic nature of Brownian motion of aerosol particles becomes obvious: the ratio of particles of which z_DD is smaller than z_MTD significantly increases. The distribution of z_MTD successfully reproduces the results of aerosol penetration obtained by the numerical solutions of the convective-diffusion equation of aerosols without neglecting the diffusion in the direction of flow, but the deposition flux obtained by the distribution of z_DD does not agree with the gradient of particle penetration, which is a numerical solution of convective-diffusion equation of aerosol particles. Consequently, it was concluded that the method of calculating the trajectories of particles directly was advantageous to evaluate the particle behavior at low Péclet numbers.

The membrane filtration properties of activated sludge and the amount of organic acid produced were explored using sludge suspensions prepared under anaerobic conditions. Membrane filtration of the supernatant separated from sludge suspensions by centrifugation revealed that metabolites produced by activated sludge microorganisms were a major factor influencing membrane fouling in membrane filtration of activated sludge. As a means to suppress the accumulation of metabolites, the replacement of treated wastewater with untreated wastewater in a batch anaerobic bioreactor was found to improve the filtration performance of activated sludge and increase the production of acetic acid, which is an important index of energy recovery. In addition, the organic composition of wastewater was found to greatly influence the membrane filtration behavior of activated sludge, and the average specific resistance of filter cake formed on the membrane surface became marked at high carbohydrate content. Regardless of the organic composition of wastewater or the sludge concentration of the suspension, however, the average specific filtration resistance could be reduced by operation to suppress the accumulation of metabolites. The results of this research are expected to contribute to the establishment of efficient operation methods for anaerobic membrane bioreactors.

Thermophysical properties of magnetic fluid (solvent, water; nanoparticulates, Mn–Zn ferrite) were elucidated in order to examine their temperature dependency in both non-magnetic and vertical magnetic fields. Heat transfer by natural convection was also investigated in a horizontal enclosed rectangular container whose bottom plate was heated uniformly in both non-magnetic and vertical magnetic fields in order to estimate the heat transfer characteristics. The results showed that the heat transfer of magnetic fluid in a horizontal enclosed rectangular container increases with increasing magnetic flux density.

With a view to controlling the melting point and extending the temperature range for practical application of calcium chloride hexahydrate as a latent heat storage material, an attempt was made in the previous study to derive an empirical equation for the melting point depression by soluble additives (Watanabe and Hirasawa, 2017). In the present study, the effect of the same nine additives on the latent heat of fusion (measured value, 182 kJ/kg) was examined. As in the case of melting point depression, the latent heat of fusion decreased with increasing amount of additive, and the effect of each additive could be expressed numerically by a simple empirical equation. Further, a constant numerical relationship was found between the melting point depression and the latent heat decrease, regardless of the type of additive.

Spent lithium ion batteries are a secondary resource of metals. To recover Li and Co ions into water, hydrothermal reactions were performed to leach cobalt and lithium from LiCoO₂ at 150–300°C for 10–60 min with 0.4 M of various acids. Sulfuric acid, nitric acid, and citric acid were introduced as leaching reagents. For 0.4 M of citric acid aqueous solution, over 90% of Li and Co ions could be leached at 150°C within 10 min. Reduction of cobalt ion (Co³⁺ to Co²⁺) is considered to be necessary for dissolution of Co ion into water solution and citric acid acted reductant. Formation of Co citrate, which was detected by UV-vis spectroscopy, was the reason why citric acid was effective for leaching LiCoO₂ with hydrothermal water.