Evaluation of submerged surface flow (SSF) constructed wetlands for recirculating tilapia production systems

A recirculating aquaculture system (RAS) treating tilapia production wastewaters used a two-step process combining a simple clarifier and a submerged surface flow (SSF) constructed wetlands for suspended solids removal and removal of nitrogenous compounds. This system successfully supported a commercial scale level of production (>35 kg/m(3)) for over 36 months of operation. The innovative SSF wetland design incorporated a high hydraulic loading rate (3.03 m/day), larger effective diameter media (380 mm), and a deeper bed depth (0.90 m) than previously suggested design guidelines. The SSF wetland flow pattern was characterized as plug flow with dispersion, but this analysis based on bed volume data indicated that media porosity was reduced from an assumed design value of 54-27% under operating conditions. The TSS, TAN, NO0-N, and NO3-N, percent mass removal for the SSF wetlands was 67.2, 46.0, 87.0, and 40.6, respectively. The TSS, TAN, NO2-N, and NO3-N mass removal for the SSF wetlands was 8.21, 0.58, 0.63, and 0.93 g/(m(2) day), respectively. Optimal performance of the SSF wetlands with simultaneous removal of TAN and NO2-N, and NO3-N occurred at TAN loadings less than 6.0 g/(m(2) day). Bed depth and hydraulic loading rates were major factors controlling this aerobic/anaerobic removal of nitrogen. The wetlands appeared to be oxygen limited at very high TAN loadings above 6.0 g/ ((2) day). Site elevation (1189 m) and warm culture temperatures (similar to 25 degrees C) contributed, but supplemental aeration could provide better TAN removal. Summary of design parameters were presented. Mean K-T values calculated for TSS, TAN, NO2-N, and NO3-N were 9.861, 0.614, 20.033, and 8.292 days(-1) compared favorably to other SSF systems. Published by Elsevier B.V.