Turbidity composition and the relationship with microbial attachment and UV inactivation efficacy

Area of Science:

• Water treatment
• Environmental microbiology
• Public health

Background:

• Turbidity-causing materials (TCMs) in water can harbor bacteria, potentially compromising drinking water safety.
• Understanding bacterial attachment to TCMs and their impact on disinfection is crucial for public health.
• TCMs can originate from water sources or treatment processes.

Purpose of the Study:

• To assess bacterial attachment to various TCMs.
• To determine the impact of TCMs on UV disinfection of bacteria.
• To evaluate the influence of different turbidity levels and TCM types on UV disinfection efficacy.

Main Methods:

• Investigated bacterial attachment of Escherichia coli and Enterococcus faecalis to chalk, Fe(III) hydroxide, kaolin clay, manganese dioxide, and humic acids at varying turbidity levels (0-5 NTU).
• Assessed the effect of TCMs on UV disinfection efficiency by measuring bacterial inactivation (log10 reduction) and UV transmittance (UVT).

Main Results:

• Bacterial attachment was highest to Fe(III) hydroxide and chalk, attributed to their more neutral surface charge.
• Humic acids and Fe(III) hydroxide significantly reduced UV transmittance (UVT) with increasing concentration, impacting UV disinfection.
• E. coli inactivation was poorest in the presence of Fe(III) at 0.2 NTU (2.5 log10 reduction at 10mJcm⁻²), compared to no TCMs (3.9 log10 reduction).
• Enterococcus faecalis exhibited greater resistance to UV irradiation than E. coli across all tested TCMs.

Conclusions:

• The type and concentration of TCMs significantly influence bacterial attachment and UV disinfection effectiveness.
• Current uniform regulations for turbidity before UV disinfection may not be universally appropriate.
• Tailoring disinfection strategies based on specific TCM characteristics is essential for ensuring safe drinking water.