At a pilot scale wastewater treatment plant ozonation and powdered activated carbon
filtration were assessed for their efficacy to remove trace organic contaminants from secondary
treated effluents. A chemical analysis of 16 organic compounds was accompanied by
a comprehensive suite of in vitro and in vivo bioassays with the focus on genotoxicity to account
for the potential formation of reactive oxidation products. In vitro experiments were
performed with solid phase extracted water samples, in vivo experiments with native
wastewater in a flow through test system on site at the treatment plant. The chemical
evaluation revealed an efficient oxidation of about half of the selected compounds by more
than 90% at an ozone dose of 0.7 g/g DOC. A lower oxidizing efficiency was observed for the
iodinated X-ray contrast media (49e55%). Activated carbon treatment (20 mg/L) was less
effective for the removal of most pharmaceuticals monitored. The umuC assay on genotoxicity
delivered results with about 90% decrease of the effects by ozonation and slightly lower
efficiency forPACtreatment. However, theAmestest on mutagenicity with the strain YG7108
revealed a consistent and ozone-dose dependent increase of mutagenicity after wastewater
ozonation compared to secondary treatment. Sand filtration as post treatment step reduced
the ozone induced mutagenicity only partly. Also the fish early life stage toxicity test revealed
an increase in mortality after ozonation and a reduced effect after sand filtration. Only
activated carbon treatment reduced the fish mortality compared to conventional treatment
on control level. Likewise the in vivo genotoxicity detected with the comet assay using fish
erythrocytes confirmed an increased (geno-)toxicity after ozonation, an effect decrease after
sand-filtration and no toxic effects after activated carbon treatment.
This study demonstrates the need for a cautious selection of methods for the evaluation
of advanced (oxidative) treatment technologies and of the effectiveness of post-treatments
for elimination of adverse effects caused by oxidative treatments case by case.