Fractionation of organic matters in sludge rejected by NF membrane

Nanofiltration membrane bioreactor (NF-MBR) was proposed to provide quality effluent free of virus and most large organic substances. The dissolved organic matter (DOM) in soluble microbial products (SMP), loosely bound extracellular polymeric substances (LBEPS) and tightly bound extracellular polymeric substances (TBEPS) of wastewater sludge before and filtered through nanofiltration membrane were fractionated using size exclusion chromatography, characterized with ultraviolet absorbance at 230, 254 and 280 nm, dissolved organic carbon (DOC) content, and excitation-emission-matrix (EEM) spectra. Except for long-chain organic acids, the membrane rejected most organic matters in SMP and LBEPS fractions. However, the membrane failed to reject fluorescent DOM from TBEPS at molecular weight of 3000–7000 Da. The content of TBEPS in the mixed liquor affected significantly the effluent quality in NF-MBR application.

This study fractionated the DOM into SMP, LBEPS and TBEPS fractions from a wastewater sludge using size exclusion chromatography, and filtered the extracted DOM using NF membrane. Fig. 3. The SEC chromatograms (LEFT) (A) 230 nm, (B) 254 nm, (C) 280 nm and EEM spectra (right) of TBEPS sample.