Biofilters made of Ulva and periphyton differ in their effectiveness in removing ammonia and nitrate from mariculture effluents. Our research evaluated the practicality of a combination of these two biofilters in improving the overall removal of dissolved N, where efficient removal of ammonia by the seaweed is followed by efficient removal of nitrate by periphyton. A paired Ulva-periphyton biofilter was exposed to various areal loads of ammonia and nitrate, the primary nitrogen forms in fishpond effluents. A first upstream macroalgae biofilter stocked with Ulva was fed with fishpond effluents at different areal loads of ammonia and nitrate, while a second downstream periphyton biofilter was paired for further nitrogen removal from the effluent. Ulva removed ammonia at a rate of 0.7–5.4 g TAN m−2 d−1, in correlation with the TAN areal load, with Vmax of 5.1 and Km of 4.4 g TAN m−2 d−1. Downstream periphyton was exposed to a lower TAN, but nitrate-rich effluent, and revealed similar capacities for the removal of both N forms, at removal rates of up to 1.7 and 1.8 g N m−2 d−1, respectively. Compared to nitrate, areal load of TAN had a greater impact on the removal dynamics of both N forms by periphyton. Overall, the paired biofilter resulted in a nearly total depletion of ammonia (97%) and efficient nitrate removal (67%), when areal loads in fishpond effluents were below 2 and 4 g N m−2 d−1 of TAN and NO3-N, respectively.
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