Controlling Of Membrane Fonling And Its Mechanism Of On-line Ultrasound In A Fluidized Bed Membrane Bioreactor

Membrane bioreactor is the sewage processing system and recycling technology that combines high efficient membrane dividing technology with biological decomposing function of active sludge; Fluidized bed is a new sewage processing technology with the advantages of both biomembrane and active sludge. Combination of fluidized bed and membrane bioreactor brings the two into full play and makes better nitrogen removal result. But membrane fouling has become "bottleneck" that restricts the. application and development of the technology.For effective control of membrane fouling in the fluidized bed membrane bioreactor, an ultrasonic fluidized bed membrane bioreactor technology was proposed in this dissertation. A long-term operating experiment of simulative sewage in daily life processed by ultrasonic fluidized bed membrane bioreactor was conducted. The eliminating effect of online ultrasonic cleansing on membrane fouling as well as effect of short-term ultrasonic on characteristic of the mixed liquor was studied and the comparison between ultrasonic fluidized bed membrane bioreactor (FMBR-US) and common fluidized bed membrane bioreactor (FMBR-C) was made. In order to reveal microbial diversity of activated sludge in both system, the sludge samples were analyzed by polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis.In the long term operation, ultrasonic fluidized bed membrane bioreactor had a obvious slower growth rate of trans-membrane pressure (TMP) than the common fluidized bed membrane bioreactor which could prolong the cleaning cycle of membrane by51%. Online ultrasound reduced the average size of sludge about94.53μm, increased the sludge exocellular polymer (EPS) content (14±5) mg· g-1and reduced the mixture soluble microbial products (SMP); in the mean while, ultrasound reduced the sludge concentration and the viscosity of the mixed sludge liquor which help to the control of membrane fouling. Analysis showed that online ultrasound could reduce the irreversible pollution on membrane surface; the main mechanism of membrane fouling was cake layer pollution in FMBR-US which accounts for86.63%of the total membrane resistance. Besides cake layer pollution, the pore adsorption was another main mechanism of membrane fouling in FMBR-C of59.26%and38.18%respectively. PCR-DGGE analysis results showed that there were both the same and the own specific microbial species in two fluidized bed membrane bioreactor. The difference of microbial diversity between the reactor and membrane was not obvious in FMBR-C while online ultrasound increased the microbial diversity and increased the differences of microbial diversity in aerobic area, anoxia area and the membrane.