| Two kinds of sub-millifiltration(SMF) modules, high-end of SMF(pore size 0.10～1.00mm) and low-end of SMF(pore size 0.01-0.10mm) were called separately module H and module L,and introduced to artificially confine high concentration sludge within one tank for favoured nutrient biodegradation and to maintain appropriate activated sludge as mixed liquor suspended solids (MLSS) in another tank for either membrane filtration or secondary sedimentation, which got rid of the limit of high concentration sludge on bioreactor wastewater treatment system.Module H was made of stainless steel mesh, (1) effects of sludge MLSS (10-30 g/L), module pore size (0.10-1.00 mm) and pressure drop (water head:30 cmH2O and 90 cmH2O) on the flux of module H were investigated, (2) effects of five different pore sizes (0.10～1.00mm) on the flux and filtrate MLSS of sub-millifiltration (SMF) were investigated by module H for separating 20g/L sludge MLSS and achieving average sludge MLSS 2-4g/L. Results showed that the flux of SMF module vs time exhibited negative exponent patterns, logarithmic of average flux had extremely notable linear relationship with sludge MLSS,module pore size and water head, and a mathematical formula J= e6.1372-0.0799C+1.0570P+0.0034H was obtained to compute the average flux of SMF module at given parameters; modules of different pore sizes could achieve separation of high concentration sludge, as far as design value(2-4g/L) was concerned, the module of pore size 0.47mm was considered to be the best choice, which achieved average sludge MLSS 3.1 g/L during the 40 min, the corresponding average flux was obtained 282.3L/(m2.h) and 30- to 60-fold higher than ultra/microfiltration, and the filtrate MLSS was relatively stable with the time change at this pore the module.Module L was made of organic polymer material, clear water experiment,pore size measure,filtering sludge test,backwashing test and surface modification of module L were investigated.Results showed (1) resistances of various kinds of module were all within 108-109 m-1, reducing by over 3-4 orders of magnitude compared to resistance of membrane,(2) the smallest and biggest intercept particle size of module were separately tested for 22.8μm and 35.3μm by solute intercept method,(3) various concentration sludge were filtered by module L, initial MLSS was obtained very lowly for 5-53mg/L and rapidly for 0, the bigger the intercept particle size, the bigger average flux of module L was obtained at the different sludge concentration,(4) air backwash was employed for cleaning of module L, the module of the biggest intercept particle size was cleaned more easily, and its flux recovery rate was the biggest. When 2g/L and lOg/L sludge MLSS were filtered by the biggest intercept particle size module, the optimal intensity of backwash and backwashing time were obtained for 10m/h and 0.5min,when 30g/L sludge MLSS was filtered, the optimal intensity of backwash and backwashing time were acquireed for 15m/h and 0.5min,(5) the surface of module L was modified by two kinds of methods ethanol process and sludge process, the filter flux was improved compared to unprocessed ones, the significance in decreased order was found to be sludge process, ethanol process and unprocessed one.Module H could be considered to be a cost effective and efficient technology for compromise separation of high concentration sludge, and provide appropriate activated sludge as mixed liquor suspended solids (MLSS) for either membrane filtration or secondary sedimentation, but initial MLSS of SMF low-end was very lowly, and could not be used for compromise separation of sludge, to realize such a goal, module L could be operated by intermittently or processed by continuously along with bypass separation of sludge to indirectly realize compromise separation of sludge. |
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