Effects of ρ(COD)/ρ(TN) on Performance and Membrane Fouling in UCT-type Submerged Membrane Bioreactor

A bench-scale UCT-type submerged membrane bioreactor was utilized to treat synthetic municipal wastewater with foucus on the influences of ρ(COD)/ρ(TN) on biological nutrients removal and membrane fouling.Results show that the process has a strong capability of anti-shock organic loading and average 89.9% of organic matter is removed,indicating chemical oxygen demand(COD) removal is irrespective of ρ(COD)/ρ(TN) ratio. The average removal efficiencies of total nitrogen(TN) and total phosphorus(TP) under ρ(COD)/ρ(TN) ratio of 7.3 are the highest at 90.27% and 92.4% respectively. Futhermore, proportions of TN removal via aerobic simultaneous nitrification and denitrification(SND) and total phosphorus removal via anoxic phosphorus removal increase to 27.9%, 44.91% from 1.6%,7.94%(ρ(COD)/ρ(TN) ratio of 3.2 to 7.3) respectively. Higher fouling rate is observed with the increasing ρ(COD)/ρ(TN) ratio which changes the nitrogen removal pathway. The increase of organic loading and decrease of dissolved oxygen induce the aerobic SND behavior that affect the phychemical properties and metabolic productions of aerobic biosolids. The sludge filterabilitydeteriorate due to higher extracellular polymeric substances(EPS) concentration normalized against mixed liquor suspended solid(MLSS) and soluble microbial products(SMP) concentration under SND condition,which also result in higher modified fouling index(MFI) values both for suspendeded solids and soluble components. Bio-floc sizes decrease slightly under the backgroud of the high air shear stresses owing to the decreased dissolved oxygen. Correlation between the fouling rate and the nitrogen reduction across the membrane via dinitrification of biofilm attached on the membrane surface is also assessed.