Data on operation and performance of cost-effective solutions for end-of-pipe removal of nitrate from land-based saltwater recirculating aquaculture systems (RAS) are scarce but increasingly requested by the aquaculture industry. This study investigated the performance of a (semi)commercial-scale fixed-bed denitrification unit using single sludge for treating effluent from a commercial, saltwater RAS used for production of Atlantic salmon (Salmo salar). A fixed-bed denitrification reactor was fed continuously with 3-days hydrolyzed sludge from the commercial RAS, and was operated at different hydraulic retention times (HRTs; 1.82, 3.64, 5.46, or 7.28 h) or influent C/N ratios (3, 5, 7, or 10). Twenty-four h pooled samples were collected from the inflowing RAS water and the hydrolyzed sludge as well as from the denitrification reactor outlet, and samples were analyzed for nutrients and organic matter content.

Nitrate removal rates increased consistently with decreasing HRT (from 64.3 ± 5.2–162.7 ± 22.0 g NO₃-N/m³/d within the HRTs tested) at non-limiting C/N ratios, while nitrate removal efficiencies decreased (from 99.6 ± 0.3–58.2 ± 8.9 %). With increasing influent C/N ratios at constant HRT (3.64 h), nitrate removal rates increased until the removal efficiency was close to 100 % and nitrate concentration in the denitrification reactor became rate-limiting. A maximum nitrate removal rate of 162.7 ± 2.0 g NO₃-N/m³/d was achieved at a HRT of 1.82 h and an influent C/N of 6.6 ± 0.5, while the most efficient use of hydrolyzed sludge (0.19 ± 0.02 g NO₃-N removed/g sCOD supplied) was obtained with a HRT of 3.64 h and a C/N ratio of 2.9. Removal rates of organic matter significantly and consistently increased with decreasing HRT and increasing C/N ratio. In addition, reducing HRT and increasing C/N ratios significantly improved removal of total phosphorus (TP) and PO₄-P.

In conclusion, optimal management of the operating parameters (HRT and C/N ratio) in a single-sludge denitrification process can significantly reduce the discharge of nitrogen, organic matter, and phosphorous from land-based saltwater RAS and thus contribute to increased sustainability.

关于从陆上盐水再循环水产养殖系统（RAS）中通过管道末端去除硝酸盐的经济有效解决方案的操作和性能的数据很少，但水产养殖业对此的要求越来越高。这项研究调查了使用半污泥处理（半）商业规模固定床反硝化装置的性能，该污泥用于处理用于生产大西洋鲑鱼（Salmo salar）的商业盐水RAS的废水）。向固定床反硝化反应器连续供应3天的商业RAS水解水解污泥，并在不同的水力停留时间（HRT; 1.82、3.64、5.46或7.28 h）或进水C / N比下运行（3， 5、7或10）。从流入的RAS水和水解污泥以及反硝化反应器出口收集了24小时的合并样品，并分析了样品中的养分和有机质含量。

在非限制性的C / N比下，硝酸盐去除率随着HRT的降低而持续增加（在测试的HRT中为64.3±5.2–162.7±22.0 g NO ₃ -N / m ³ / d），而硝酸盐去除效率则有所降低（从99.6± 0.3–58.2±8.9％）。随着恒定HRT（3.64 h）进水C / N比的增加，硝酸盐的去除率增加，直到去除效率接近100％，反硝化反应器中的硝酸盐浓度成为速率限制。在HRT为1.82 h和进水C / N为6.6±0.5的条件下，最大硝酸盐去除率达到162.7±2.0 g NO ₃ -N / m ³ / d，而水解污泥的使用效率最高（0.19±0.02）克₃获得了-N去除/提供的g sCOD），HRT为3.64 h，C / N比为2.9。随着HRT的降低和C / N比的提高，有机物的去除率显着且持续增加。另外，降低HRT和提高C / N比可显着提高总磷（TP）和PO ₄ -P的去除率。

总之，单污泥反硝化过程中操作参数（HRT和C / N比）的最佳管理可以显着减少陆基盐水RAS中氮，有机物和磷的排放，从而有助于提高可持续性。