Fouling characterization in entrapped cells-based-membrane bioreactor treating wastewater

- Entrapped cell-membrane bioreactor (MBR) delayed fouling condition.
- Treatment performances of entrapped cell- and suspended cell-MBRs were comparable.
- Pore blocking was the main fouling cause in entrapped cell- and suspended cell-MBRs.
- Extracellular substance and product releases were limited in entrapped cell-MBR.

Membrane fouling in an entrapped cells-based-membrane bioreactor (E-MBR) treating synthetic medium strength municipal wastewater was investigated. Laboratory scale models of E-MBR and regular (suspended cell) membrane bioreactor (S-MBR) were operated in parallel. The two systems showed comparable performances on organic matter and nutrient removal. The removal efficiencies of soluble chemical oxygen demand and ammonia of E-MBR were 95.6 ± 0.9% and 92.6 ± 2.1% while those of S-MBR were 95.8 ± 0.8% and 93.3 ± 0.8%. Membrane fouling was monitored based on transmembrane pressure through a constant permeate flux at 10.63 L/m2·h. Due to lower concentrations of bound extracellular polymeric substances (bEPS) and soluble microbial products (SMP), E-MBR experienced less fouling and provided longer operation time before required chemical cleaning compared to S-MBR (16 days for E-MBR and 9 days for S-MBR). bEPS in E-MBR consisted of higher molecular weight compounds and had a broader molecular weight distribution than those in S-MBR. The Fourier transform infrared analysis of bEPS suggested proteins and carbohydrates as major components. According to the 3-dimension fluorescence excitation-emission matrix spectra, SMP in E-MBR were mainly tryptophan, protein-like and humic acid-like substances, while those in S-MBR were mainly humic acid-like substances, hydrophobic acid substances and fulvic acid substances. The particles size of sludge in E-MBR was smaller than that in S-MBR. The delayed membrane fouling in E-MBR is a great advantage as it lowers costs associated with membrane cleaning processes and prolongs the membrane lifespan.

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