Effects Of Inorganic Particles On The Dynamic Membrane Structure And Filtration Behavior In The Dynamic Membrane Bioreactor

Dynamic membrane bioreactor(DMBR)rely on in-situ formed dynamic membrane(DM)on inexpensive filtration materials with large pore size to reject fine particles in wastewater,which exhibits a great potential for achieving excellent effluent quality with low transmembrane pressure and high flux.Therefore,DMBR had attracted extensive attention in wastewater treatment and reuse in recent years.Inorganics particles are common components of wastewater,the inorganics will become a component of DMs when using DMBRs to treat domestic wastewater.However,the effects of inorganic particles with different sizes and their interactions with microorganisms on the formation,structure,and filtration resistance of DMs in DMBRs are unclear.In present study,eight lab-scale and one pilot-scale DM based filtration processes were set up to investigate the effects of inorganic particles and their interaction with biofilms on DM structure,DM component and long-term filtration behavior.Following conclusion had been obtained from this study:(1)When only large inorganic particles(e.g.,sands and 1.3-69.2 μm)were added in the influent,the effluent turbidity was still higher than 2.26 NTU within 50 days,which indicated that an effective DM had not been formed for more than 50 days,but on the basis of this experiment,the effluent turbidity was smaller than 0.6 NTU within eight days when the influent changed into added small inorganics particles(e.g.,clays and 0.5-2.7 μm),suggesting that an effective DM was formed on the support mesh.When the influent contained only natural clays,or both sands and clays,the effluent turbidity decreased to less than 1 NTU in about 20 days,10 days,respectively.Sands and clays promoted effective DM formation synergistically in the processes without feeding organics.(2)When the influent contained biodegradable organics,biofilms could grow on the support mesh as a major component of DMs.Which could achieve long-term stable operation with low effluent turbidity(< 1 NTU)and low TMP(< 10 Pa).This demonstrated that pure biofilms without containing inorganic particles were ideal materials for DMs.(3)Inorganic particles in simulated wastewater could affect DMs structure,which in return affects the filtration performance of DMBRs,and their negative effects were size dependent.The large inorganic particles(e.g.,sands and 1.3-69.2 μm)in wastewater could disturb the DM structures and result in unstable effluent turbidity.The small inorganic particles in wastewater,e.g.,natural clays(0.5–2.7 μm),were very liable to deposit on the support materials to form thick and compact DMs.In addition,the addition of inorganic particles in the mixed liquor affects bacterial community structure and increases the biomass and EPS contents in DMs,which decreased the DM porosity and enhanced the filtration resistance of DMBR.(4)The small inorganic particles(1.1-2.3 μm)in wastewater could accumulate on the membrane surface and become a part of DM,which increased DM density and decreased porosity and thus,rapid rising in membrane resistance occurred in pilot-scale DMBR.Therefore,removing the inorganic particles in wastewater as many as possible when using DMBR to treat actual municipal wastewater.