Total suspended solids (TSS) concentration is an important aquaculture indicator that affects the growth of farmed animals and relates to the effective utilization of dissolved oxygen (DO). To evaluate the TSS removal efficiency of a self-designed vertical-flow sedimentation tank in Litopenaeus vannamei culture, we determined its hydraulic parameters and monitored changes in water quality before and after sedimentation. The results show that under the culture conditions of this experiment, the influent flow rate of this settling tank was (779.47±18.19) m·h^–1, the hydraulic retention time was (1.09±0.03) h, and the removal rate of TSS concentration was (78.09±1.35)%, exhibiting a significant sedimentation effect. Among the water quality indicators, the TSS concentration and dissolved oxygen (DO) concentration of the influent water were significantly higher than those in the effluent water (p<0.05). At the late stage of culture, the ammonia nitrogen ( ${\mathrm{N}\mathrm{H}}_4^{+}\text{-}\mathrm{N}$) concentration increase significantly, the nitrite nitrogen ( ${\mathrm{N}\mathrm{O}}_2^{-}\text{-}\mathrm{N}$) concentration decrease and the TSS concentration decreased significantly. During the use of the settling tank, pH and total alkalinity (T-Alk) exhibited an increasing trend. Correlation analysis of water quality factors show that influent TSS concentration was significantly negatively correlated with nitrite concentration, ${\mathrm{N}\mathrm{H}}_4^{+}\text{-}\mathrm{N}$ concentration was significantly positively correlat with pH and negatively correlated with ${\mathrm{N}\mathrm{O}}_2^{-}\text{-}\mathrm{N}$ concentration. ${\mathrm{N}\mathrm{O}}_3^{-}\text{-}\mathrm{N}$ concentration was significantly positively correlated with pH and significantly negatively correlated with DO concentration (p<0.05). There was a significant positive correlation between ${\mathrm{N}\mathrm{H}}_4^{+}\text{-}\mathrm{N}$ concentration and pH in the effluent, and a significant positive correlation between ${\mathrm{N}\mathrm{O}}_3^{-}\text{-}\mathrm{N}$ concentration and both pH and T-Alk (p<0.05). The correlation coefficients of pH and T-Alk for influent and effluent water were 0.8 and 0.7, respectively. Based on water quality indicators and their correlation analysis, it is recommended to moderately increase the sedimentation tank volume, enhance airlift aeration intensity, and reduce hydraulic retention time. Meanwhile, aquatic microorganisms should be regulated in a targeted manner through the adjustment of water nutrients to further reduce the volume and frequency in aquaculture management. The sedimentation-reflux of aquaculture water using sedimentation tanks features simple operation and energy saving, which is suitable for large-scale implementation.

Nitrogen pollution often restricts the stable operation of the culture system during the indoor culture of Penaeus monodon. The encapsulated denitrifying bacterial capsule technology based on high-permeability fiber membranes has been applied in aquaculture water treatment. In this study, the system with encapsulated denitrifying bacterial capsules was set as the experimental group, and the system without capsules as the control group. Dynamic monitoring of water quality indicators was carried out, combined with scanning electron microscopy (SEM) to analyze the structural changes on the surface of the encapsulated bacterial membrane, and metagenomic sequencing technology was employed to characterize the microbial communities in both the water and bacterial capsules, aiming to explore its in-situ regulation effect and mechanism on aquaculture water quality. The results show that the ammonia nitrogen ( ${\text{NH}}_4^{+}\text{-N}$) in the experimental group peaked on day 12 at a concentration of 1.42 mg·L⁻¹, which was 4 d earlier than that in the control group with a lower peak concentration. The nitrite nitrogen ( ${\text{NO}}_2^{-}\text{-N}$) in the experimental group peaked on Day 20 at a concentration of 2.80 mg·L⁻¹, 20 d earlier than that in the control group, with a peak concentration reduction of 69.5%. The fiber spacing of the encapsulated bacterial membrane increased, and distinct microbial adhesion and deposition structures formed on its surface. The diversity and richness of the microbial community inside the encapsulated bacterial membrane increased significantly (p<0.05). The species richness of the microbial community in the water of the experimental group was higher than that of the control group, and was highly similar to the microbial composition of the encapsulated bacterial membrane. The dominant bacterial phyla were mainly Pseudomonadota and Bacteroidota, while the dominant genera at the genus level included Nitrospira, Winogradskyella, etc. The abundances of denitrification and nitrification related functional genes as well as nitrogen metabolism pathways in the experimental group were all higher than those in the control group. This study reveals the physical protection of denitrifying functional bacteria by the fiber membrane encapsulation system and its ecological regulatory effect on the microbial community, demonstrating that the addition of encapsulated denitrifying bacteria can improve the nitrogen accumulation status in aquaculture water, enhance the functional characteristics related to nitrogen metabolism, and thereby achieve in situ regulation of water quality.