Effect of chemical and biological surfactants on activated sludge of MBRsystem: Microscopic analysis and foam test

A bench-scale MBR unit was operated, under stressing condition, with the aim of stimulating the onset offoaming in the activated sludge. Possible synergies between synthetic surfactants in the wastewater andbiological surfactants (Extra-Cellular Polymeric Substances, EPSs) were investigated by changing C/Nratio. The growth of filamentous bacteria was also discussed. The MBR unit provided satisfactory overallcarbon removal overall efficiencies: in particular, synthetic surfactants were removed with efficiencyhigher than 90% and 95% for non-ionic and ionic surfactants, respectively. Lab investigation suggestedalso the importance to reduce synthetic surfactants presence entering into mixed liquor: otherwise, theirpresence can significantly worsen the natural foaming caused by biological surfactants (EPSs) producedby bacteria. Finally, a new analytic method based on ‘‘ink test’’ has been proposed as a useful tool toachieve a valuation of EPSs bound fraction.