N. Al-Jassim, M.I. Ansari, M. Harb, P.-Y. Hong
Water Research 73, 277-290, (2015)
Antibiotic resistance, Conventional activated sludge processes, Microbial contaminants, Microbial risk, Water reuse
This study aims to assess the removal
efficiency of microbial contaminants in a local wastewater treatment
plant over the duration of one year, and to assess the microbial risk
associated with reusing treated wastewater in agricultural irrigation.
The treatment process achieved 3.5 logs removal of heterotrophic
bacteria and up to 3.5 logs removal of fecal coliforms. The final
chlorinated effluent had 1.8 × 10(2) MPN/100 mL of fecal coliforms and
fulfils the required quality for restricted irrigation. 16S rRNA
gene-based high-throughput sequencing showed that several genera
associated with opportunistic pathogens (e.g. Acinetobacter, Aeromonas,
Arcobacter, Legionella, Mycobacterium, Neisseria, Pseudomonas and
Streptococcus) were detected at relative abundance ranging from 0.014 to
21 % of the total microbial community in the influent. Among them,
Pseudomonas spp. had the highest approximated cell number in the
influent but decreased to less than 30 cells/100 mL in both types of
effluent. A culture-based approach further revealed that Pseudomonas
aeruginosa was mainly found in the influent and non-chlorinated effluent
but was replaced by other Pseudomonas spp. in the chlorinated effluent.
Aeromonas hydrophila could still be recovered in the chlorinated
effluent. Quantitative microbial risk assessment (QMRA) determined that
only chlorinated effluent should be permitted for use in agricultural
irrigation as it achieved an acceptable annual microbial risk lower than
10(-4) arising from both P. aeruginosa and A. hydrophila. However, the
proportion of bacterial isolates resistant to 6 types of antibiotics
increased from 3.8% in the influent to 6.9% in the chlorinated effluent.
Examples of these antibiotic-resistant isolates in the chlorinated
effluent include Enterococcus and Enterobacter spp. Besides the presence
of antibiotic-resistant bacterial isolates, tetracycline resistance
genes tetO, tetQ, tetW, tetH, tetZ were also present at an average 2.5 ×
10(2), 1.6 × 10(2), 4.4 × 10(2), 1.6 × 10(1) and 5.5 × 10(3) copies per
mL of chlorinated effluent. Our study highlighted that potential risks
associated with the reuse of treated wastewater arise not only from
conventional fecal indicators or known pathogens, but also from
antibiotic-resistant bacteria and genes.
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