Abstract The current study combined P and N removal using organic flocculant chemicals and woodchip bioreactors in both freshwater and brackish water (7 ppm) recirculating aquaculture systems (RAS). The use of carbon (C) containing flocculant chemicals in the process was hypothesized to further stimulate C-demanding N removal (denitrification) in bioreactors. The trial of combined P and N removal consisted of four treatments: freshwater and brackish water RAS with and without the addition of supernatant from flocculation process to the woodchip reactor. Duplicate woodchip reactors were used per treatment and the trial was run for six weeks. 56% and 49% of P was removed from fresh and brackish sludge water, respectively. The nitrate-N (NO3-N) removal rate was improved in the treatment when supernatant from flocculation process was used together with RAS discharge water when compared against the control. In brackish water RAS, the improvement was more pronounced (from 6.6–16.5 g NO3-N m−3 d-1) than in freshwater RAS (from 5.1–6.5 NO3-N m−3 d-1). In the freshwater bioreactors using supernatant, N was largely discharged as a nitrite-N (NO2-N). High NO2-N concentrations in freshwater reactors allude to incomplete denitrification reactions taking place. The results suggest that the organic flocculants did provide an additional C source for denitrification, which improved the N-removal process. However, in freshwater RAS this might have been partly due to untargeted processes such as DNRA (dissimilatory nitrate reduction to ammonium), and/or insufficient denitrification reactions taking place (excessive NO2-N production).

中文翻译：

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淡水和微咸水的排放管理 RAS：有机絮凝剂除磷和木片反应器除氮相结合

摘要 当前的研究在淡水和微咸水 (7 ppm) 再循环水产养殖系统 (RAS) 中使用有机絮凝剂化学品和木片生物反应器结合去除 P 和 N。假设在该过程中使用含碳 (C) 的絮凝剂化学品可进一步刺激生物反应器中需要 C 的 N 去除（反硝化）。联合去除 P 和 N 的试验包括四种处理：淡水和微咸水 RAS，有和没有从絮凝过程中向木片反应器添加上清液。每次处理使用重复的木片反应器，试验进行了六周。分别从新鲜和微咸污泥水中去除了 56% 和 49% 的 P。与对照相比，当絮凝过程的上清液与RAS排放水一起使用时，处理中硝酸盐-N（NO3-N）的去除率得到提高。在微咸水 RAS 中，改进（从 6.6-16.5 g NO3-N m-3 d-1）比在淡水 RAS（从 5.1-6.5 NO3-N m-3 d-1）更明显。在使用上清液的淡水生物反应器中，N 主要以亚硝酸盐-N (NO2-N) 的形式排放。淡水反应堆中的高 NO2-N 浓度暗示正在发生不完全的反硝化反应。结果表明，有机絮凝剂确实为反硝化提供了额外的 C 源，从而改善了 N 去除过程。然而，在淡水 RAS 中，这可能部分是由于非目标过程，如 DNRA（异化硝酸盐还原为铵），