Adhesion strength and spreading characteristics of EPS on membrane surfaces during lateral and central growth

Analysis of wastewater treatment plant data identifies the drivers of PFAS enrichment in foams

The concept of incorporating foam fractionation in aerated bioreactors at wastewater treatment plants (WWTPs) for the removal of per- and polyfluoroalkyl substances (PFAS) has recently been proposed. The extent of PFAS enrichment in aerated bioreactors' foams, as indicated by enrichment factors (EFs), has been observed to vary widely. Laboratory evidence has shown that factors affecting PFAS enrichment in foams include conductivity, surfactant concentrations and initial PFAS concentrations. However, real wastewaters are complex heterogenous matrices with physical, chemical and biological characteristics potentially contributing to the phenomenon of PFAS partitioning into foams. In this study, we characterised mixed liquor suspensions, including conductivity, filament content, aqueous PFAS concentrations, surface tension and total suspended solids concentrations (TSS) as well as foams, including bubble size and half-life. We used statistical tools - linear mixed-effects model - to establish relationships between PFAS enrichment in aerated bioreactor foams and the examined characteristics. We found that some of the examined characteristics, specifically filament content, surface tension and TSS concentrations measured in mixed liquor suspension and foam half-life, are negatively and significantly associated with the enrichment of longer chain PFAS (with perfluorinated carbon number ≥ 6). Of these, filament content is the important determinant of PFAS enrichment, potentially leading to an increase in, for example, perfluorooctanoic acid (PFOA) EF from 3 to 100 between typical filamentous and non-filamentous suspended biomass. However, enrichment of shorter chain PFAS (with perfluorinated carbon number ≤ 5) is negligible and is not affected by the characteristics that were measured. The findings of our study may serve as valuable information for the implementation of foam fractionation at WWTPs by elucidating the drivers that contribute to the enrichment of longer chain PFAS, under conditions typically found at WWTPs.

Characterization of the Initial Fouling Layer on the Membrane Surface in a Membrane Bioreactor: Effects of Permeation Drag

In this study, the properties of the initial fouling layer on the membrane surface of a bioreactor were investigated under different operating modes (with or without permeate flux) to improve the understanding of the effect of permeation drag on the formation of the initial fouling layer. It was found that protein was the major component in the two types of initial fouling layers, and that the permeation drag enhanced the tryptophan protein-like substances. The attraction of the initial foulants to the polyvinylidene fluoride (PVDF) membrane was ascribed to the high zeta potential and electron donor component (γ-) of the membrane. Thermodynamic analyses showed that the permeation drag-induced fouling layer possessed high hydrophobicity and low γ-. Due to permeation drag, a portion of the foulants overcame an energy barrier before they contacted the membrane surface, which itself possessed a higher fouling propensity. A declining trend of the cohesive strength among the foulants was found with the increasing development of both fouling layers.

The characterization and comparison of exopolysaccharides from two benthic diatoms with different biofilm formation abilities

Exopolysaccharide (EPS) of two benthic diatoms, Amphora sp. and Stauroneis sp., with different biofilm formation abilities were investigated. The ratio of suspension-cells/biofilm-cells was employed to indicate the diatom biofilm formation abilities. The soluble EPS from the supernatant of whole culture, tightly bound EPS from floating cells, loosely and tightly bound EPS from biofilm cells were fractionated as SL-EPS, F-TB-EPS, BF-LB-EPS and BF-TB-EPS, respectively. The analysis for productions and monosaccharide compositions indicated that EPS from two diatoms were different in terms of the productions, distributions, and monomer compositions. Amphora sp. produced more (1.5-fold) total exopolysaccharides, but less (<0.4-fold) BF-TB-EPS than Stauroneis sp. The monosaccharides of the EPS from Amphora sp. were more diverse than those of Stauroneis sp., with 13 and 10 monomers, respectively. Neutral sugars, Glc, Xyl and Man, were abundant in Stauroneis sp., while Gal, Glc and Xyl were rich in Amphora sp. Uronic acid and hexosamine were present in all fractions of two diatoms, especially Glc-A being the most abundant monomer in SL-EPS of Amphora sp. It was proposed that the high content of uronic acid (especially Glc-A) might be crucial for the strong biofilm formation abilities of Amphora sp.