Estimation of the solid–liquid mass transfer coefficient is important for the design and operation of mixing equipment. The solid–liquid mass transfer coefficient increases with impeller rotational speed up to the minimum impeller rotational speed for complete suspension N_js, after which the rate of increase ratio declines. Therefore, the estimation of N_js is a key point for solid–liquid mixing. In this study, N_js based on the solid–liquid mass transfer coefficient (Kamei et al., 2008) was compared with N_js based on dimensional analysis (Zwietering, 1958). The following new correlation of N_js based on power consumption was derived by correction of the correlation of Zwietering (1958).

This study examined the factors influencing the filtration of particles and the removal of viruses during the purification of polluted water containing the viruses. We observed that viruses were adsorbed on the surface of fine particles, and the particles aggregated at certain concentrations of particles and viruses. The average specific resistance of the filter cake formed on the membrane surface decreased owing to the coarsening of particles by the viruses. This phenomenon was significantly influenced by the solution environment. When the pH of the solution was below the isoelectric point of the viruses, the increase in particle size and removal of viruses became significant. At a pH of 4.5, the average specific cake resistance decreased to approximately 1/3, and removal of viruses was 99.999% or higher. Even when the large pore size of the membrane made their capture difficult, viruses were adsorbed onto the particles and captured as a filter cake. In addition, when viral solution permeated the cake, adsorption of viruses was facilitated, and their removal increased. In experiments with for four types of fine particle and two types of virus, the viruses were found to be adsorbed onto a variety of fine particles. In each case, the pH of the polluted water significantly influenced the adsorption characteristics. Adsorption of viruses onto diatomaceous earth could be achieved by controlling the pH, and the viruses were removed by the diatomaceous earth precoat layer.

The seawater quality in a storage tank of Pseudocardium sachalinense and Megangulus venulosus fitted with a foam separator in summer and winter was investigated with the aim of building a seawater quality control system. The prototype foam separators tested were found to remove pollutants from the storage tank. In summer, the deterioration of seawater quality in the storage tank could be controlled by use of the foam separator, and the mortality rate of Megangulus venulosus decreased. In winter, the quality of seawater in the storage tank fitted with a foam separator was equivalent to that of fresh seawater.

For oxidation of gaseous VOCs, a solid catalyst of platinum black coated on alumina balls is generally used. Because platinum is an expensive and rare noble metal, the catalytic activity of the cheaper noble metal silver was tested. It was found that catalytic performance was improved by increasing the quantity of silver added, but not to the level of the platinum catalyst. Based on the results, we tried heat treatment of the supporting alumina balls to prevent the diffusion of silver and achieve an uneven distribution of silver on the surface of the alumina balls. It was found that the catalytic performance could be greatly improved, but not to the level of the platinum catalyst.