A study on the enhancement of environmental durability of EPDM rubber materials for the aerator membrane was performed using a butyl rubber as a modifier. A conventional EPDM rubber formulation was evaluated as having about 26.0 wt% or more oil content from the chloroform immersion test. These oils would be gradually and continuously deleted from the aerator membrane when directly exposed to a waste-water or chemically corrosive fluids, making the membrane less flexible and the performance worse. To improve this, a butyl rubber (IIR) was utilized as the modifier for a low-ENB type of EPDM rubber formulation with low-oil content. The environmental durability of the IIR-modified EPDM rubber material was expected to be greatly enhanced compared to the conventional one. However, the mechanical and performance properties such as elongation, tensile strength, and air bubble size, etc. were still maintained as good as in the conventional one. Furthermore, TGA analysis of the IIR-modified EPDM material showed that there would be partially compatible between IIR and EPDM. It also showed that the initial degradation temperature of the IIR-modified EPDM could be somewhat increased, exhibiting the enhanced compatibility among the components and, thereby, more enhanced environmental durability.

In the present paper, batch and semi-continuous settling characteristics of a binary calcium carbonatewater system were investigated. Using experimental data of batch settling characteristics, a graphical analysis for a semi-continuous thickening column was developed and compared with experimental results on the basis of Kynch theory, only where the feed velocity line was within the limits of Kynch theorem Ⅲ. The analysis showed good agreement with experiments. Quite erroneous results, however, was observed for the analysis of a sludge region on the underloaded operation, which was considered due to the deviation from the limits of theory.