Low concentrations of Al(III) accelerate the formation of biofilm: Multiple effects of hormesis and flocculation

Abstract Residual Al(III) (at low concentration) is common in water treatment plants (WTPs) and is associated with bacteria. We hypothesize that Al(III) accelerate biofouling due to its hydrolysis and hormesis characteristics, as compared with other cations. To verify this, we elaborated the roles of Al(III) at low concentrations on the biofilm formation. Al(III) hormesis ( NH 2 and/or NH on the leaked protein, contributed to biofilm formation. Biofilm maturity was aided by polysaccharides, which shielded Al(III) toxicity for the formed biofilm. Thus, the biofilm exhibited a distinguished double-layer microstructure, principally with proteins and inactivated cells at the bottom, polysaccharides and activated cells at the top. Thus, hormesis and flocculation caused by low concentration Al(III) mutually promoted each other, and together accelerated biofilm formation.