Abstract
Constructed wetlands (CWs) are environmentally-friendly methods for mariculture wastewater purification. The hydraulic regime is a key factor in the effectiveness of sub-surface flow CW treatment. The objectives of this study were to investigate the effects of five hydraulic operating regimes (i.e. Intermittent, Continuous, Batch I, Batch II and Batch III) on the purification performance of CW treated with mariculture wastewater and to assess the correlations between enzyme activities (i.e. urease, dehydrogenase) and purification performance of CW. Fifteen pilot sub-surface CWs with Salicornia bigelovii were investigated for the performance of CW as well as urease activity (UA) and dehydrogenase activity (DA). Over the experiment, removal efficiencies of TAN, NO3−-N, TN and COD under five hydraulic operating regimes were 26.6 to 37.2%, −6.0 to 16.5%, 9.4 to 16.8% and 33.9 to 44.6% respectively, corresponding to removal rates of 147.6 to 456.9 mg m−2 d−1, −18.1 to 229.2 mg m−2 d−1, 174.0 to 603.6 mg m−2 d−1 and 501.9 to 1421.6 mg m−2 d−1 respectively. CW with a Batch III operating regime had the best treatment performance, with mean removal efficiencies of TAN, NO3−-N, TN and COD of 37.2%, 16.5%, 14.9% and 34.0% respectively, with the corresponding removal rates of 456.9, 229.2, 603.6 and 873.6 mg m−2 d−1. As for enzyme activities, the UA was significantly higher in CW under Batch II than in Intermittent and Continuous operating regimes and the DA in CW with Batch I was significantly higher than under an Intermittent operating regime. UA and DA had significant positive correlations with COD concentrations but negative correlations with TAN and TN concentrations. The correlation analysis results showed that UA and DA can be an important indicator in evaluating removal performance of CW with Salicornia bigelovii in marine aquaculture wastewater treatment.