Aerobic denitrification microbes have great potential to solve the problem of NO₃⁻-N accumulation in industrialized recirculating aquaculture systems (RASs). A novel salt-tolerant aerobic denitrifier was isolated from a marine recirculating aquaculture system (RAS) and identified as Halomonas alkaliphile HRL-9. Its aerobic denitrification performance in different dissolved oxygen concentrations, temperatures, and C/N ratios was studied. Investigations into nitrogen balance and nitrate reductase genes (napA and narG) were also carried out. The results showed that the optimal conditions for nitrate removal were temperature of 30 °C, a shaking speed of 150 rpm, and a C/N ratio of 10. For nitrate nitrogen (NO₃⁻-N) (initial concentration 101.8 mg·L⁻¹), the sole nitrogen source of the growth of HRL-9, the maximum NO₃⁻-N removal efficiency reached 98.0% after 24 h and the maximum total nitrogen removal efficiency was 77.3% after 48 h. Nitrogen balance analysis showed that 21.7% of NO₃⁻-N was converted into intracellular nitrogen, 3.3% of NO₃⁻-N was converted into other nitrification products (i.e., nitrous nitrogen, ammonium nitrogen, and organic nitrogen), and 74.5% of NO₃⁻-N might be converted to gaseous products. The identification of functional genes confirmed the existence of the napA gene in strain HRL-9, but no narG gene was found. These results confirm that the aerobic denitrification strain, Halomonas alkaliphile HRL-9, which has excellent aerobic denitrification abilities, can also help us understand the microbiological mechanism and transformation pathway of aerobic denitrification in RASs.

Wetland plants that cover the wetlands play an important role in reducing pollutants. The aim of this study was to investigate the effect of two plant species on microbial communities and nitrogen-removal genes and to evaluate the contributions of absorbing pollutants by Canna indica (CI) and Cyperus alternifolius (CA) to the removal performance in both a vertical subsurface flow constructed wetland and a horizontal subsurface flow constructed wetland, which were part of a full-scale hybrid constructed wetland system. The microbial assemblages were determined using 16S rRNA high-throughput sequencing. Results showed that the presence of CI and CA positively affected microbial abundance and community in general and which was positive for the total bacteria and ammonia nitrogen removal in the CWs. The higher abundance of Nitrospirae appeared in the non-rhizosphere sediment (NRS) than that in the rhizosphere sediment (RS). More denitrification genes were found in NRS than in RS. The copy numbers of narG, nirS and nosZ genes for CA were higher than those for CI. Wetland plant species can significantly (P < 0.05) affect the distribution of microbial communities in RS. Plant selection is important to promote the development of microbial communities with a more active and diverse catabolic capability and the contribution of plant absorption to the overall removal rate of wetland system can be neglected.

The toxicity of nanomaterials to microorganisms is related to their dose and environmental factors. The aim of this study was to investigate the shifts in the microbial community structure and metabolic profiles and to evaluate the environmental factors in a laboratory scale intertidal wetland system exposed to zinc oxide nanoparticles (ZnO NPs). Microbial assemblages were determined using 16S rRNA high-throughput sequencing. Community-level physiological profiles were determined using Biolog-ECO technology. Results showed Proteobacteria was the predominant (42.6%–55.8%) phylum across all the sediments, followed by Bacteroidetes (18.9%–29.0%). The genera Azoarcus, Maribacter, and Thauera were most frequently detected. At the studied concentrations (40 mg·L⁻¹, 80 mg·L⁻¹, 120 mg·L⁻¹), ZnO NPs had obvious impacts on the activity of Proteobacteria. Adverse effects were particularly evident in sulfur and nitrogen cycling bacteria such as Sulfitobacter, unidentified_Nitrospiraceae, Thauera, and Azoarcus. The alpha diversity index of microbial community did not reflect stronger biological toxicity in the groups with high NP concentrations (80 mg·L⁻¹, 120 mg·L⁻¹) than the group with low NP concentration (40 mg·L⁻¹). The average well color development (AWCD) values of periodically submersed groups were higher than those of long-term submersed groups. The group with NP concentration (40 mg·L⁻¹) had the lowest AWCD value; those of the groups with high NP concentrations (80 mg·L⁻¹, 120 mg·L⁻¹) were slightly lower than that of the control group. The beta diversity showed that tidal activity shaped the similar microbial community among the periodically submerged groups, as well as the long-term submerged groups. The groups with high DO concentrations had higher diversity of the microbial community, better metabolic ability, and stronger resistance to ZnO NPs than the groups with a low DO concentration.

An integrated constructed wetland-microbial electrolysis cell (ICW-MEC) system was investigated for nitrogen removal under different pollution loads, hydraulic loads (HLRs), and aeration conditions. The treatment performance of each unit and the microbial community characteristics for nitrogen removal were elucidated. The results showed that, on average, 80% of NH₄⁺-N, around 70% of nitrate nitrogen (NO₃⁻-N), and 70% of total nitrogen (TN) were removed by the system under three pollution loads, with less influence by pollution loads. The high removal efficiencies of NH₄⁺-N (81.8%), NO₃⁻-N (71.4%), and TN (72.8%) indicated tolerable to high HLRs. The intermittent aeration negatively affected NH₄⁺-N removal, while increasing NO₃⁻-N and TN removals by 3.2–13.0% and 3.7–16.7%. The contribution efficiencies of the secondary unit to the removal of NH₄⁺-N, NO₃⁻-N, TN, and total organic carbon (TOC) reached 47.4%, 55.0%, 45.9%, and 38.8%, respectively. The distinct microbial communities existed in various units of the ICW-MEC system, which were strongly affected by environmental factors and shaped by diverse fillers and structures of the system. The dominant bacteria contributed to the efficient nitrogen removal performance of the ICW-MEC system. The three units exerted their advantages to ensure efficient and stable system operation.