Bacteria associated with granular activated carbon particles in drinking water

Area of Science:

• Environmental Microbiology
• Water Treatment Technology
• Public Health

Background:

• Granular activated carbon (GAC) filters are widely used in drinking water treatment.
• Microbial colonization of filter media can impact water quality.
• Understanding particle release and microbial attachment is crucial for assessing treatment efficacy.

Purpose of the Study:

• To develop and validate a sampling protocol for detecting bacteria on particles from GAC filters.
• To quantify the prevalence of heterotrophic plate count (HPC) and coliform bacteria attached to carbon fines.
• To investigate the potential for these bacteria-laden particles to compromise drinking water safety.

Main Methods:

• A gauze filter/Swinnex procedure was employed to collect carbon fines from 201 GAC-treated drinking water samples over 12 months.
• Homogenization and modified most-probable-number (MPN) and membrane filtration techniques were used for bacterial enumeration.
• Scanning electron microscopy (SEM) was utilized to visualize bacterial microcolonies on carbon particles.

Main Results:

• 41.4% of samples contained HPC bacteria attached to carbon particles, with 8.6 times higher recovery rates than conventional methods.
• Over 17% of samples had carbon particles colonized with coliform bacteria, with recovery rates 122–1,194 times higher than standard procedures.
• Nearly 28% of attached coliforms were of the fecal biotype; SEM revealed bacterial microcolonies on particle surfaces.

Conclusions:

• Bacteria readily attach to carbon fines released from GAC filters.
• Carbon fines carrying bacteria may serve as a pathway for microbial penetration of water treatment barriers.
• This mechanism poses a potential risk to the microbiological safety of potable water supplies.