Membrane Fouling Characteristics Of Nitrogen And Phosphorus Removal Membrane Bioreactor

The membrane bioreactor(MBR) has many advantages,such as a small footprint,high quality effluent,strong impact.However,membrane fouling is a key problem blocking the wide application of this process.Most studies focused on the membrane fouling factors in aerobic MBR.As the more stringent effluent standards to nitrogen and phosphorus,nitrogen & phosphorus removal MBR(for short NR-MBR) is gradually showing its advantages,and its fouling characteristics is different from ordinary aerobic MBR.Thus,this paper compared the ability to remove pollutants and membrane fouling of the nitrogen & phosphorus removal MBR and aerobic MBR in different sludge age.In this thesis,sludge age(SRT),extracellular polymer(EPS),soluble microbial products(SMP) and the temperature influences on the membrane fouling rate were inveatigated.The main experiment results and conclusions are as follows.(1) COD_Cr in the influent maintained at 500～600mg/L,and the hydraylic retention(HRT) wsa 12h,SRT did not have a big impact on the COD removel efficiencies.In the three stages of SRT for 5d,15d,30d,the average COD removal rate of nitrogen & phosphorus removal MBR and ordinary aerobic MBR could reach 96.6%.(2) SRT for 15d,in the NR-MBR,nitrogen and phosphorus removal efficiency was significantly.The average total nitrogen removal rate reached 80%,the concentration of phosphorus in effluent was maintained below 0.5mg/L,with the average removal rate of 96.3%.(3) NR-MBR is different from aerobic MBR with respect of membrane fouling pattern. The former mainly comes from pore blocking fouling,while the latter mainly comes from the absorption layer cake.In addition,the former fouling rate was significantly lower than the latter(4) Membrane fouling in NR-MBR presented two stages.The pressure difference raised quickly after over 0.014Mpa.The fouling rate was smallest at SRT is 15d,and the system could operation for a long time.(5) Sludge morphology in the NR-MBR is very sound,but massive filamentous bacteria appeared the aerobic MBR,which resulted in seriously membrane fouling.In the same reactors,the fouling rates and sludge concentrations was positive correlation.(6) A proportional relationship was found between sludge settlement and EPS in sludge. The membrane fouling rate raised as the EPS increased.The declined proportion of protein of EPS would speed up the formation of membrane fouling.(7) The longer SRT,the higher SMP concentration.The SMP in aerobic MBR was slightly higher than it in NR-MBR.However,the SMP in effluent was three times larger.NR-MBR have better interception on SMP,also one of the membrane fouling substances.(8) Various pools of nitrogen & phosphorus removal MBR had different ability on SMP degradation.Aerobic microbial released more polysaccarides than anaerobic microbial.