| By using the regular water-quality indices and the terrestrial ecotoxicological methods of inhibiting seed germination and root elongation, the ecological risk of the DAT-IAT process for municipal wastewater treatment was assessed. The results of regular water-quality indices determination showed that COD and SS in treated wastewater by the DAT-IAT process could attain the National Integrated Wastewater Discharge Standard. Although NH+4-N could also meet the standard, most of nitrogen could not be removed out of the wastewater because of the N-form changing from NH+4-N to NO-3-N. Thus, the ecological risk of eutrophication could not successfully be reduced. The results based on the determination of ecotoxicological indices showed that IC50 of COD in wastewater from inflow water, DAT and effluent toxic to the germination of wheat seeds decreased gradually. The IC50 of the inhibitory rate of seed germination was 249.3 mg·L-1, 165.3 mg·L-1 and 161.2 mg·L-1, respectively, and the IC50 of the inhibitory rate of root elongation was 257.6 mg·L-1, 154.0 mg·L-1 and 142.1 mg·L-1, respectively. It thus revealed that the ecotoxicity of wastewater increased after treatment by the DAT-IAT process, which demanded more studies to address the regulation of the ecological risk. In particular, the inhibition of wheat root elongation was far more sensitive than the germination of wheat seeds under the same water-quality conditions. Thus, the root elongation could be recommended as a sensitive method to assess ecological risk of wastewater treatment effluents. |
