NOM removal through coagulation, sedimentation and filtration as a remedial action to prevent adverse effects of re-growth in networks / Fjerning av NOM ved koagulering, sedimentering og filtrering som tiltak mot biofilmdannelse i ledningsnett for drikkevann
A qualitative and quantitative monitoring of biofilm formation was performed in four categories of water: raw water, filtered water (after removal of natural organic matter (NOM)), disinfected water and distributed water. The biofilm formation was reduced by 95–99 % as a result of the NOM removal, a reduction considerably more significant than indicated by the change in biodegradable organic carbon in the water. The biofilm formation was almost constant in the distribution system regardless of residence time. The mould in the biofilm changed from excess growth in biofilm grown in raw water to marginal or no growth in treated water or distributed water. The amount of bacteria in the biofilm was considerably reduced during the treatment, and particularly low in biofilm grown in water taken shortly after disinfection. Presumptive Pseudomonas, presumptive Aeromonas, coliform bacteria and E. coli were identified in biofilm grown in raw water, but not in biofilm grown in treated water or distributed water. Presumptive Legionella was identified in biofilm grown in raw water, in water after NOM removal but before disinfection and in distributed water. Confirmed Legionella was identified in biofilm grown in water after NOM removal and during distribution.