Influence of Legionella pneumophila Viability States on Colonization in Granular Activated Carbon Filters

Abstract

Legionella is an important opportunistic pathogen in drinking water distribution and premise plumbing systems. This study investigated the potential growth of Legionella pneumophila during granular activated carbon (GAC) filtration, considering their viability states in the filter beds. Laboratory-scale biologically active GAC columns were used, and L. pneumophila cells were spiked with different viability states (culturable, viable but non-culturable (VBNC), and dead cells). The gene concentrations in the effluents were monitored for 70 days. In columns spiked with the culturable cells, high levels of L. pneumophila were detected in the effluents even after 70 days of operation, suggesting that the GAC filter bed could serve as an ecological niche for L. pneumophila colonization. However, when VBNC-cells were introduced, the levels of L. pneumophila in the effluents were significantly lower, though still higher than in the column spiked with dead cells. This suggested that the growth potential of L. pneumophila was influenced by their viability states in the influent water. These findings underscored the ecological potential for Legionella regrowth and emphasized the necessity of monitoring their behavior during GAC treatment, particularly when incomplete inactivation during ozonation is concerned.

Keywords

• legionella
• granular activated carbon
• viable but non-culturable
• biofilm
• spiking experiment