On the shrinking and hardening of EPDM rubber membranes in water sanitation filtration tanks

A water reclamation plant (WRP) uses a fine bubble-diffuser system to treat biological sewage waste. The process involves pumping air through slits in rubber membranes to feed bacteria in the waste stream. This case study deals with problems encountered with shrinking and hardening of the EPDM rubber membranes. Several factors affecting the performance of the rubber were investigated, including leaching of plasticizers, accelerated cross-linking due to the effects of temperature, and vulcanization effects on rubber flexibility. Different rubber materials were evaluated (i.e. silicone, Hypalon, Viton, neoprene, and a different formulation of the EPDM rubber). The investigation found that EPDM compound 7195 provided superior performance and met the required parameters for the wastewater treatment application. Additional investigations revolved around improving pumping losses in membrane through optimized perforation sizes and the inclusion of a cooling system (water misting or heat-exchanger) to cool the air before it reaches the membrane. (C) 2003 Elsevier Ltd. All rights reserved.