Conventional wastewater treatment plants are ineffective in removing a broad range of micropollutants,
resulting in the release of these compounds into the aquatic environment, including natural drinking
water resources. Ozonation is a suitable treatment process for micropollutant removal, although,
currently, little is known about the formation, behavior, and removal of transformation products (TP)
formed during ozonation. We investigated the elimination of 30 selected micropollutants (pharmaceuticals,
X-ray contrast media, industrial chemicals, and TP) by biological treatment coupled with ozonation
and, subsequently, in parallel with two biological filters (BF) or granular activated carbon (GAC) filters.
The selected micropollutants were removed to very different extents during the conventional biological
wastewater treatment process. Ozonation (specific ozone consumption: 0.87 ± 0.29 gO3 gDOC
1 , hydraulic
retention time: 17 ± 3 min) eliminated a large number of the investigated micropollutants. Although 11
micropollutants could still be detected after ozonation, most of these were eliminated in subsequent GAC
filtration at bed volumes (BV) of approximately 25,000 m3 m3
. In contrast, no additional removal of
micropollutants was achieved in the BF. Ozonation of the analgesic tramadol led to the formation of
tramadol-N-oxide that is effectively eliminated by GAC filters, but not by BF. For the antiviral drug
acyclovir, the formation of carboxy-acyclovir was observed during activated sludge treatment, with an
average concentration of 3.4 ± 1.4 mg L1 detected in effluent samples. Subsequent ozonation resulted in
the complete elimination of carboxy-acyclovir and led to the formation of N-(4-carbamoyl-2-imino-5-
oxo imidazolidin)-formamido-N-methoxyacetetic acid (COFA; average concentration: 2.6 ± 1.0 mg L1
).
Neither the BF nor the GAC filters were able to remove COFA. These results highlight the importance of
considering TP in the evaluation of advanced wastewater treatment processes. The results further
indicate that post-treatment of ozonated wastewater with GAC filtration seems to be more suitable than
BF, due to the sorption of formed TP to the activated carbon.