Removal of nutrients from aquaculture wastewater using cattail (Typha spp.) constructed wetlands

The aquaculture industry is among the fastest growing food production sectors in the world. Land-based aquaculture systems continue to increase in popularity as they offer the benefits of controlling diseases, managing water quality, and minimizing threats to wild populations of fish. However, these systems discharge wastewater high in N and P. The ability of cattail (Typha spp.) constructed wetlands (CWs) to remove N and P from aquaculture wastewater (AWW) was examined here. Cattail CWs were established in mesocosms and had a gradient of AWW applied weekly for a total of 5 weeks. Total N and P loadings ranged from 13.7 to 209.2 mg m⁻² and 3.01 to 45.97 mg m⁻² over 28 days, respectively. Additions of AWW did not cause elevations in total dissolved N, total ammonia N, or nitrite N in CW water; however, concentrations of nitrate N and P in CW water were related to nutrient loading conditions. Elevations in P persisted for 3–4 weeks among high nutrient loading treatments, providing an opportunity for eutrophic conditions to develop in CW systems. However, after 33 days of treatment, >95% total P concentration reduction was achieved in all mesocosms with final concentrations <0.05 mg L⁻¹, equivalent to reference conditions. High-loading treatments achieved greater P load reduction (856.8–955.0 mg m⁻² year⁻¹) than low-loading and reference treatments (591.7–792.7 mg m⁻² year⁻¹). This study demonstrates the effectiveness of cattail CWs to remove nutrients during AWW treatment and highlights the potential for end-of-season use in northern climates, providing insights regarding the operational timeline of such systems.