New fundamental insights on biofouling during gravity-driven membrane filtration.
The use of filtration technologies has emerged as being a solution to current issues in global water security.
The use of filtration technologies has emerged as being a solution to current issues in global water security. Access to clean and safe water for millions of people around the world is achievable through Gravity Driven Membrane (GDM) filtration technologies, which require no energy input, specialized equipment or high pressures; simply gravity. While GDM offers an attractive solution, it is not exempt from biofouling, a caveat to filtration known as biofilm mediated membrane fouling.
Mr Peter Desmond from Dr Nicolas Derlon’s lab at Eawag (Zurich, Switzerland) recently published a study in Water Research entitled: “Linking composition of extracellular polymeric substances (EPS) to the physical structure and hydraulic resistance of membrane biofilms” on the fundamental aspects of fouling in GDM systems. Their study highlights that hydraulic resistances caused during GDM fouling are dependent on the biofilm’s chemical composition (EPS composition) and structural profile (thickness and density), all of which are linked to the nutrient profile of the water feeding the system. This finding is indeed a significant one, as this helps bring a step closer to accurately managing fouling events in GDMs, while at the same time, predict GDM performance based on water quality being filtered.
I, for one, will be on a lookout for exciting follow-up studies concerning GDM from Mr Desmond, Dr Derlon and his team in the very near future...
The effect of extracellular polymeric substances (EPS) on the meso-scale physical structure and hydraulic resistance of membrane biofilms during gravity driven membrane (GDM) filtration was investigated. Biofilms were developed on the surface of ultrafiltration membranes during dead-end filtration at ultra-low pressure (70 mbar). Biofilm EPS composition (total protein, polysaccharide and eDNA) was manipulated by growing biofilms under contrasting nutrient conditions. Nutrient conditions consisted of (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), and (iii) a nitrogen limitation (C: N: P ratio: 100:0:10). The structure of the biofilm was characterised at meso-scale using Optical Coherence Tomography (OCT). Biofilm composition was analysed with respect to total organic carbon, total cellular mass and extracellular concentrations of proteins, polysaccharides, and eDNA. 2D-confocal Raman mapping was used to characterise the functional group composition and micro-scale distribution of the biofilms EPS. Our study reveals that the composition of the EPS matrix can determine the meso-scale physical structure of membrane biofilms and in turn its hydraulic resistance. Biofilms grown under P limiting conditions were characterised by dense and homogeneous physical structures with high concentrations of polysaccharides and eDNA. Biofilm grown under nutrient enriched or N limiting conditions were characterised by heterogeneous physical structures with lower concentrations of polysaccharides and eDNA. For P limiting biofilms, 2D-confocal Raman microscopy revealed a homogeneous spatial distribution of anionic functional groups in homogeneous biofilm structures with higher polysaccharide and eDNA concentrations. This study links EPS composition, physical structure and hydraulic resistance of membrane biofilms, with practical relevance for the hydraulic performances of GDM ultrafiltration.
Reference: Desmond P, Best JP, Morgenroth E, Derlon N. Linking composition of extracellular polymeric substances (EPS) to the physical structure and hydraulic resistance of membrane biofilms. Water. Res. 2017 Dec 27;132:211-221. doi: 10.1016/j.watres.2017.12.058. [Epub ahead of print]