Study On Membrane Fouling And Its Control Of Dynamic Membrane Bioreactor

Dynamic membrane bioreactor(DMBR) is a new wastewater treatment by combining the dynamic membrane filtration technology with biological wastewater treatment process. Besides its the traditional advantages, the membrane bioreactor(MBR) also has the characteristics of low power consumption and low cost; therefore it is a promising sewage and wastewater treatment technology. However, the application of DMBR and MBR technology is limited by membrane fouling. This study intended to delay and control the membrane fouling by adding fly ash, and provide experimental basis for the practical application.Contrast experiments were conducted by using non-woven film substrate, and two types of anoxic, anaerobic and aerobic dynamic membrane bioreactor(inverted A2/O-DMBR). Influence on the control and delay of membrane fouling was found by observing pollutants removal rates and sewage mixture of reactor A(without adding the modified fly ash) and reactor B(adding the modified fly ash). The experimental results showed when the two reactors ran continuously 40 d without discharging sewage, the average removal rates of COD 、NH3- N 、TN and TP from reactor A and the reactor B were 92.4%, 95.4%, 70.67%, 65.78% and 94.7%, 97.8%, 69.53%, 97.8% respectively, and the removal rate of the conventional indexes of reactor B was significantly higher than reactor A except the TN.Extracellular polymers(EPS) was the main material that affected the membrane fouling. With the increase of the running time, the concentration of the EPS(mg/g MLVSS) of the aerobic pool of the reactor A and B was increased from 2.7 to 10.9 and 2.6 to 11.7. The protein and polysaccharide were the primary components of the EPS. When the protein content increased, the membrane pollution aggravated. In the whole operation process, the ratio of the each pool reaction of the reactor A and B present first increased and then changed from 8.2 to 21 and 8.5 to 26, with the peak in 12 d and 18 d respectively. EPS was divided into two types- close extracellular polymers(TB-EPS) and loose extracellular polymers(LB- EPS). When the LB- EPS content increased, the membrane flux declined and the membrane fouling aggravated. When the trend of the TB- EPS/LB-EPS of the reaction pool changed similarly, ie, all first increased and then decreased, the ratio of the each pool reaction in reactor A and reactor B were from 4.5 to 31.5 and from 4.5 to 36 respectively, and the peak was in the 15 d and 25 d respectively.When the running processes of reactor A and reactor B were compared, it was found the membrane flux of the reactor A were reduced from 71.1 L/(m2.h) to 16.1(L/m2.h), and reactor B were reduced from 72.4 L/(m2. h) to 15.8 L/(m2. h). The size of the sludge particles(d50) in reactor A and B was 52.44 um and 52.78 um respectively when the membrane hanged first. With the extension of running process, the size of the sludge particles(d50) in reactor A reached the peak, 63.78μm when running 10 d while the sludge particles in reactor B reached the peak, 79.5μm. When the membrane fouling increased, the membrane module needed to be cleaned. The first clean cycle of reactor A was 5 days while reactor B was 8 days. In the whole process, the running time of reactor A was shorter, the membrane flux was irreversibly declined to 25 d, and the membrane fouling was serious while reactor B could run for a longer time, 36 d. It showed that adding the modified fly ash could effectively delay membrane fouling and make membrane cleaning cycle longer.