Treatment of rainbow trout farm effluents in constructed wetland with emergent plants and subsurface horizontal water flow

The objective of this research was to investigate treatment of aquaculture effluents of flow-through systems in created wetlands. The constructed wetlands types used in this study were subsurface root zone systems with emergent plants and horizontal effluent soil percolation. Three 1.40 x 1.00 x 0.70 in (L x W x H) root zone systems were filled with sands of 1-2 mm particle size and planted with 20 rooted shoots of reed per square meter (Phragmites australis). Nutrient removal of rainbow trout (Oncorhynchus mykiss) effluents flowing through the wetland was determined for hydraulic loading rates of 1, 3 and 5 1/min corresponding to very short hydraulic residence times (HRTs) of 7.5, 2.5 and 1.5 h, respectively. Inflowing nutrients were removed within every continuously flooded wetland. Total suspended solids (TSS) and chemical oxygen demand (COD) were reduced by 95.8-97.3% and 64.1-73.8%, respectively, and demonstrated no influence of HRT. Total phosphorus (TP) and total nitrogen (TN) removal rates varied from 49.0% to 68.5% and 20.6% to 41.8%, respectively, and were negatively correlated with HRTs. Effluent purification was best at HRT of 7.5 h, but sufficient removal rates were achieved for shorter HRTs. (C) 2003 Elsevier Science B.V. All rights reserved.