Ecotoxicological properties of wastewater treated using tertiary
Department of Chemical Engineering, Chemical
Process Engineering Laboratory, Aristotle University of Thessaloniki and
Chemical Process Engineering Research Institute,6th km Harilaou Thermi
Road, 57001 Thessaloniki, Greece.
The objective of this work was the examination of the
efficiency of coagulation and ozonation processes for the production of
reclaimed wastewater with low toxicity. Municipal secondary effluents
were treated by FeCl3, Al2(SO4)3 (alum), and a commercial substance at
metal ion concentrations of 0.5 and 1 mmol/L. Alternatively, the
effluents were treated by ozonation in a semibatch ozone reactor. The
feed gas was introduced at a flowrate of 3 L/min containing ozone at
various concentrations, ranging between 2.5 and 8 mg/L; ozone residence
times were 2, 5, 15, and 30 min. The toxic effects of the advanced
treated effluents were examined by a battery of tests using the marine
bacteria Vibrio fischeri, the freshwater crustaceans Daphnia magna,
Daphnia pulex, and Thamnocephalus platyurus, and the rotifers Brachionus
calyciflorus. The addition of alum decreased the toxic effect of
reclaimed wastewater on immobilization of D. pulex, from 90 to 60%.
Ozonation was also effective for toxicity removal, which decreased to
25% effect on D. pulex after treatment by 2.5 mg O3/L for 2 min.
However, acute toxic effects after ozonation, were observed on V.
fischeri and were related to ozone gas concentration and contact time.
At the highest ozone dosage, the toxicity reached almost 100% inhibition
of bioluminescence after 15 min. The toxicity of the ozonated effluents
to bacteria decreased with sample storage time and was almost negligible
after 48 h, indicating that the potential adverse effect of reclaimed
wastewaters on receiving waters might be reduced by storage for a
certain time. Copyright 2006 Wiley Periodicals, Inc.
PMID: 16841328 [PubMed - indexed for MEDLINE]