The structure of denitrifying microbial communities in constructed mangrove wetlands in response to fluctuating salinities.

In this study, the experimental vertical-flow constructed wetland (CW) systems planted with the salt-tolerant mangrove species Kandelia candel were established to investigate the influence of salinity fluctuations on the denitrification performance and denitrifying microbial community structure of the CWs. The high-throughput sequencing analysis showed that 10-13 genera aerobic microbes had been enriched in the upper layer of wetland matrix in the depth of 10-25 cm, with the relative abundance accounting for 19.1 ±â€¯7.9%. Although the ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were inhibited significantly in the CW systems with salinity levels in the range of 0.9-1.8%, the aerobic denitrifying (AD) bacteria including Pseudomonas, Acinetobacter and Aeromonas, removed 99% of ammonia nitrogen from the influent by heterotrophic nitrification (HN) functions, and conducted denitrification at the same time to remove 90% of the TN in the system, indicating that the wetland test system successfully enriched a variety of aerobic denitrifying bacterial communities under different salinity conditions. Not only the nitrogen removal efficiency but also the adaptability of the wetland system to salinity fluctuations had been improved by the enriched HN-AD bacteria. In addition, HN-AD bacterial communities can conduct both nitrification and denitrification in the middle and upper layers of the vertical flow wetland, hereby saving the reaction space of the constructed wetland and reducing the construction cost.

Isolation and identification of a salt-tolerant aerobic denitrifying bacterial strain and its application to saline wastewater treatment in constructed wetlands.

A salt-tolerant aerobic denitrifying bacterium, Zobellella denitrificans strain A63, was isolated, and its effects on the efficiency of denitrification of saline wastewater and the denitrifying microbial community structure in the matrix were studied in vertical-flow constructed wetlands (VFCWs). In a VFCW system with strain A63, the removal efficiencies of NH4+-N, NO3--N, and total nitrogen reached 79.2%, 95.7%, and 89.9%, respectively. Quantitative PCR analysis indicated that the amoA gene from ammonia-oxidizing archaea (AOA) was highly abundant, whereas amoA from ammonia-oxidizing bacteria and nxrA from nitrite-oxidizing bacteria were lowly abundant because of the influent salinity, irrespective of whether strain A63 was added. However, the addition of strain A63 significantly increased the abundance of nirK in the top layer of the VFCW. Therefore, AOA-driven partial nitrification and aerobic denitrification by strain A63 occurred in VFCWs. Our findings suggest that adding salt-tolerant denitrifying strains to constructed wetlands can enhance denitrification for saline wastewater treatment.

The influence of complex fermentation broth on denitrification of saline sewage in constructed wetlands by heterotrophic nitrifying/aerobic denitrifying bacterial communities.

An experimental vertical-flow constructed wetland (CW) was tested to treat salt-containing sewage. CW clogging deposits and withered Pontederia cordata L. were collected into a complex fermentation broth to serve as the carbon source and its effects on the denitrification capacity and microbial composition of the CW were examined. Addition of the complex fermentation broth into the CW influent (1.8% salinity) led to high removal efficiencies of NH4+-N > 99.82 ±â€¯0.00% and TN > 90.39 ±â€¯0.05%. Heterotrophic nitrifiers and aerobic denitrifiers were entirely dominant in the middle and upper layers of the CW, where obligate halophilic, aerobic denitrifiers Zobellella occurred. The CW successfully cultivated and enriched heterotrophic nitrifying-aerobic denitrifying bacteria, overcoming the effects of salinity and insufficient organic carbon sources on the denitrification capacity of CW. This type of complex carbon sources can also facilitate the utilization of waste resources, such as CW clogging deposits and withered wetland plants.

Effect of plant-based carbon sources on denitrifying microorganisms in a vertical flow constructed wetland.

The effects of supplementing plant-based carbon sources, fermented tissues of Arundo donax and Pontederia cordata, and a combination of the two plants, on the nitrogen removal efficiency and microbial composition in a vertical flow constructed wetland (VFCW) were examined. The results showed that the addition of the composite carbon source produced the highest removal efficiencies of NH4+-N 91.5%, NO3--N 94.5% and TN 92.8% in VFCW. The detected abundance of amoA, nirS, and nxrA genes indicated that ammonia oxidation bacteria and denitrifying bacteria were more abundant than the nitrite oxidation bacteria. Furthermore, the addition of the composite carbon source significantly promoted the growth of the denitrifying bacteria in VFCW. The results indicated that supplementing the system with plant-based carbon sources achieved partial nitrification and denitrification, as well as classic denitrification in VFCWs. The study suggested that multiple nitrogen removal pathways were required to feasibly and efficiently remove nitrogen.