Treatment wetlands, taking ideas from constructed wetlands and engineered wastewater treatment systems, are emerging as an engineering approach to sustainably treat a range of effluent, including aquaculture wastes. Marine wastewater adds an extra challenge in that there is salt in the effluent making it difficult to land apply on freshwater plants. This project, a multi-institution collaboration, takes advantage of macrophytes (plants) whose roots and affiliated bacterial communities can remove ammonia, nitrite, nitrate, carbon, and phosphorus from marine aquaculture wastewater. By using salt tolerant plants (e.g. Juncus sp; Spartina sp; Distichlis sp) these systems seem effective at removing nutrients in salt water and then reusing or redirecting treated water.
The current study was done in triplicate with three different species of plants (Distichlis spicata, Juncus roemerianus, and Spartina alterniflora) in combinations (by themselves; with one other plant species; or all three plant species). Once plants begin to grow and bacterial communities are developed, the nutrients were removed quite effectively. Preliminary findings indicate approximately 91% ammonium reduction in treatments containing J. roemerianus. Phosphate reductions of 22% occurred in the treatment consisting of both J. roemerianus and D. spicata. The treatments consisting of all three species achieved 95% reduction of combined nitrate and nitrite.
A number of key engineering parameters are needed to predictably design these systems: Temperature effects (on both plants and bacteria); an understanding of the ‘warm up’ time; rates of nutrient removal and thus effective hydraulic retention time; as well as optimum plant selections (single species or mixed). Data from this study will contribute to our understanding of how to optimally design floating treatment wetlands to remediate nutrients from marine aquaculture wastewater.
Keywords: Recirculating aquaculture system, ammonia, plants, phosphorus, biofiltration.