Influence of COD:N ratio on sludge properties and their role in membrane fouling of a submerged membrane bioreactor

• Published in: Water research (Oxford) Vol. 89; pp. 132 - 141
• Main Authors: Hao, L., Liss, S.N., Liao, B.Q.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.02.2016
• Subjects: Biological Oxygen Demand Analysis; Bioreactors; Carbohydrates - chemistry; COD:N; EPS; Extracellular polymeric substances; Fouling; Industrial wastewater; Membrane bioreactor; Membrane fouling; Membranes; Membranes, Artificial; Microorganisms; Nitrogen - chemistry; Photoelectron Spectroscopy; Polymers; Proteins - chemistry; Receiving; Sewage - chemistry; Sewage - microbiology; Sludge; Sludge properties; Spectroscopy, Fourier Transform Infrared; Waste Disposal, Fluid - methods; Waste Water - chemistry; Waste Water - microbiology; X-ray photoelectron spectroscopy; Industrial wastewater; Membrane bioreactor; Extracellular polymeric substances; COD:N; Sludge properties; Membrane fouling
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2015.11.052

The effect of COD:N ratio on sludge properties and their role in membrane fouling were examined using a well-controlled aerobic membrane bioreactor receiving a synthetic high strength wastewater containing glucose. Membrane performance was improved with an increase in the COD/N ratio (100:5–100:1.8) (i.e. reduced N dosage). Surface analysis of sludge by X-ray photoelectron spectroscopy (XPS) indicates significant differences in surface concentrations of elements C, O and N that were observed under different COD/N ratios, implying changes in the composition of extracellular polymeric substances (EPS). Fourier transform-infrared spectroscopy (FTIR) revealed a unique characteristic peak (CO bonds) at 1735 cm−1 under nitrogen limitation conditions. Total EPS decreased with an increase in COD/N ratio, corresponding to a decrease in the proteins (PN) to carbohydrates (CH) ratio in EPS. There were no significant differences in the total soluble microbial products (SMPs) but the ratio of PN/CH in SMPs decreased with an increase in COD/N ratios. The results suggest that EPS and SMP composition and the presence of a small quantity of filamentous microorganisms played an important role in controlling membrane fouling. [Display omitted] •An increase in COD:N ratio led to improved membrane performance.•Surface concentrations of elements O and N and C bonds are different under different COD:N ratios.•Bound EPS/SMP composition is more important than the quantity in controlling membrane fouling.•The presence of a small quantity of filamentous microorganisms led to improved membrane performance.•A characteristic peak of FTIR at 1735 cm−1 was observed for sludge under N deficiency.