Additional control indexes should be considered for the operation and design of post-treatment systems, as the wastewater treatment objectives are developing toward protecting the safety of ecological environments. In this study, two control indexes were selected and examined systematically in pilot-scale shallow open-water unit (SOWU) ponds for domestic effluent polishing: micropollutants and biotoxicities. The total risk quotient (RQTotal ≤ 1) and effect-based trigger value (EBT) were set as the thresholds for known micropollutants and biological effects, respectively. The results showed that RQTotal of micropollutants (n = 46) could be mitigated to an acceptable level and the luminescent bacteria toxicity was in compliance with the EBT after SOWU polishing in the warm season. The reduction of micropollutants and biotoxicities in the SOWUs both fit the k-C* model well (R2 > 0.9) in the warm and cold seasons. Finally, the k-C* model integrated with the control indexes was developed to design the SOWU dimensions, and the results indicated that a pond area of 21.7-108.5 m2 was required for every 1 m3/d of effluent when micropollutants were set as the control index, while a pond area of 3.6-18.2 m2 was required when luminescent bacteria toxicity was set as the control index.
Keywords: Biotoxicity; Ecological safety; Effluent; Micropollutant; k–C* model.
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