Determination of fouling-related critical flux in self-forming dynamic membrane bioreactors: Interference of membrane compressibility

A new measurement protocol was proposed for appropriate determination of the fouling-related critical flux of highly compressible self-forming dynamic membranes (SFDMs) developed on coarse-pore supporting materials. Intermittent relaxation periods and parallel clean water filtration tests were incorporated into the common transmembrane pressure (TMP) step method to minimize the interference of SFDM compressibility on fouling-related critical flux determination and to better understand the filtration characteristic of SFDMs. The average fouling-related critical flux of SFDMs determined by the new measurement protocol turned out to be significantly higher than that obtained with the common measurement protocol. This is attributed partly to the exclusion of the flux reduction associated with SFDM compression by conducting the parallel clean water filtration tests, and partly to the minimization of the effect of "continuous" compression on the structure and fouling propensity of SFDMs by integrating the intermittent relaxation periods. The intermittent relaxation periods also prevented the occurrence of irreversible fouling and steady compression of SFDMs, embodied by the relatively smaller and faster disappeared hysteresis observed in the new measurement protocol. As one way to control SFDM compression, intermittent effluent production mode appears to be a potentially promising strategy for further optimization of SFDMBR operation. Stepwise increment of relaxation time and proper selection of higher initial TMP turned out to be the options recommended for reducing the time consumption of the new measurement protocol.