University of Duisburg-Essen, Germany
Title: Seven deadly sins in membrane biofouling
Biography: Hans-Curt Flemming
Biofouling is caused by biofilms, but not all biofilms cause biofouling. Only if biofilm growth and effects exceed a given threshold of interference in a membrane process, the quest for reasons begins and if everything else is excluded, biofouling remains as a kind of “joker”. The first intuitive response of the operator is to “disinfect” the system. However, this does not necessarily work and if so, not for a long time. Here we address the most common mistakes of operation and maintenance of membrane plants in terms of biofouling, which we call “deadly sins”: 1. ignoring that nutrients are potential biomass and removal of biologically degradable organic carbon or phosphate from the water by pre-treatment would restrict biofilm accumulation; 2. Unintentional dosing of nutrients after pre-treatment, undoing the effect of pre-treatment. Organic acids, antiscalants and even biocides can be biodegradable, supporting biofilm growth; 3. Killing instead of cleaning: Biofouling is essentially caused by extracellular polymeric substances (EPS) produced by the bacteria. Inactivation only, will leave biomass and thus, the problem in place. Cleaning is more important than killing; 4. No early warning systems. All water systems bear biofilms but only the excess of biofilm effects above threshold of interference causes problems. Early warning of (sudden) biofilm accumulation enables earlier and more effective corrective actions. Monitors are available but usually considered as too expensive, although their use may considerably reduce costs; 5. Rely only on conventional feed spacer design in membrane elements. With a modified spacer design, biofilm effects can be reduced; 6. Ignorance about advanced technologies e.g., feed flow reversal in pressure vessels, pressure vessel loop operation, hybrid membrane systems and others; 7. Sticking to high flux membrane systems. A high flux sounds attractive, but compacts the EPS in biofilms, leading to increasing hydraulic resistance. If the scientific laws for biofilm formation and development are acknowledged and followed, it is possible to live with biofilms and successfully manage biofouling.