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This study explores nitrogen removal performance, bioelectricity generation, and the response of microbial community in two novel tidal flow constructed wetland-microbial fuel cells (TFCW-MFCs) when treating synthetic wastewater under two different chemical oxygen demand/total nitrogen (COD/TN, or simplified as C/N) ratios (10:1 and 5:1). The results showed that they achieved high and stable COD, NH4 +-N, and TN removal efficiencies. Besides, TN removal rate of TFCW-MFC was increased by 5-10% compared with that of traditional CW-MFC. Molecular biological analysis revealed that during the stabilization period, a low C/N ratio remarkably promoted diversities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the cathode layer, whereas a high one enhanced the richness of nitrite-oxidizing bacteria (NOB) in each medium; the dominant genera in AOA, AOB, and NOB were Candidatus Nitrosotenuis, Nitrosomonas, and Nitrobacter. Moreover, a high C/N ratio facilitated the growth of Nitrosomonas, while it inhibited the growth of Candidatus Nitrosotenuis. The distribution of microbial community structures in NOB was separated by space rather than time or C/N ratio, except for Nitrobacter. This is caused by the differences of pH, dissolved oxygen (DO), and nitrogen concentration. The response of microbial community characteristics to nitrogen transformations and bioelectricity generation demonstrated that TN concentration is significantly negatively correlated with AOA-shannon, AOA-chao, 16S rRNA V4-V5-shannon, and 16S rRNA V4-V5-chao, particularly due to the crucial functions of Nitrosopumilus, Planctomyces, and Aquicella. Additionally, voltage output was primarily influenced by microorganisms in the genera of Nitrosopumilus, Nitrosospira, Altererythrobacter, Gemmata, and Aquicella. This study not only presents an applicable tool to treat high nitrogen-containing wastewater, but also provides a theoretical basis for the use of TFCW-MFC and the regulation of microbial community in nitrogen removal and electricity production.

This study investigated synthetic wastewater treatment under low inflow C/N ratio and characterized NO3−–N-transforming and electricity-producing bacteria in a multi-anode tidal constructed wetland–microbial fuel cell (TFCW–MFC). The optimal concurrent average removal rates of NH4+–N and NO3−–N were 73% and 78%, respectively, under a flood/rest/flood time of 4 h/2h/4h in “tide” mode accompanied by one recirculation. The lowest NO3−–N concentration among all anodes was observed when the electrode gap was 45 cm. Similarly, the 45 cm anode exhibited selective enrichment of Variovorax and Azoarcus. Correction analysis showed that the high relative abundance of Azoarcus was crucial in enhancing NO3−–N removal, and the internal resistance significantly decreased as the relative abundance of Acidovorax increased. These results suggest that NO3−–N removal and bioelectricity generation can be promoted in a TFCW–MFC with limited carbon by improving the culture conditions for specific genera.

Increasing attention has been given to the treatment of livestock and poultry wastewater because of its high ammonium nitrogen (NH4+-N) content and low carbon/nitrogen ratio (C/N). Ceramic filter medium (CFM) and dewatered aluminum sludge (DAS), which are products from cast-off materials, are used as small-scale combined biological filters (CFM-DAS) for wastewater treatment. The high and stale removal efficiency of chemical oxygen demand (COD), NH4+-N, and total nitrogen (TN) in the DAS filter indicate that DAS plays a major role in pollutant removal. Although significant differences are found between the composition of nitrifying bacteria in CFM and DAS, the structures of nitrifying communities are evenly distributed in each layer of CFM or DAS irrespective of the running time. Microbial compositions are attributed to the comprehensive effect of various environmental factors such as pH and TN at effluents. In the DAS, Nitrosospira shows significant negative correlation with the concentrations of NH4+-N in effluents, whereas it has positive correlation with NO3&minus, N, and Nitrososphaera has a significant negative correlation with NO3&minus, N in effluents. Pearson correlation test reveals that certain genera may be used in estimating or predicting NH4+-N consumption and NO3&minus, N accumulation in CFM-DAS for treating sewage with a high NH4+-N content.

Mitochondrial DNA (mtDNA) polymerase chain reaction (PCR) technology has recently been developed to identify sources of fecal contamination, but information regarding environmental fate of mtDNA is limited. In this study, quantitative real-time PCR was used to determine the persistence of three species-specific mtDNA markers (human, pig and chicken) in river microcosms under different laboratory conditions and in dialysis tubes incubated in river environments during different seasons. Human feces had a higher abundance of mtDNA marker than pig and chicken feces. A biphasic decay pattern was observed for the mtDNA markers in microcosms incubated in darkness, and T90 (time needed for 90% reduction) ranged from 2.03 to 13.83 d. Each species-specific mtDNA marker persisted for relatively longer time at lower temperatures, and light exposure and predation increased the decay rates. Field experiments showed that the mtDNA markers could survive for longer time in winter (T90: 1.79-4.37 d) than in summer (T90: 0.60-0.75 d). Field application of mtDNA technology indicated that the markers were mainly distributed on the sites near animal breeding plants and had lower abundance in downstream water of the receiving river. This study expands our knowledge of the environmental fate of mtDNA markers and the results may be useful for practical application of the technology in fecal source tracking.

A novel tidal flow constructed wetland coupled with a microbial fuel cell system (TFCW-MFC), using the influent chemical oxygen demand (COD)/total nitrogen (TN) ratio of 10:1 (Device A) and 5:1 (Device B), systematically assessed nitrogen attenuation and power production performance; the spatiotemporal distribution characteristics of denitrifying functional genes and their relationship with nitrogen removal were also determined. The results showed that the TFCW-MFC achieved high removal efficiencies for COD and TN, with both devices above 95% and 83%, respectively. The maximum power density showed a notable increase from 16.97 in Device B to 25.78 mW/m3 in Device A. The distribution of the Shannon index indicated that the diversity of napA, nirK, and nirS were higher at the cathode layers in two devices. The high COD/TN ratio obviously increased the nirK diversity in anode on the 30th day, while a low COD/TN ratio apparently promoted the diversities increase of narG, nirK, and nirS in upper or bottom layers. Proteobacteria was the dominant phylum in both devices, and the composition differentiation of the dominant denitrifying genera was mainly affected by the space variation, specifically the nitrogen concentration, pH, dissolved oxygen, and their collaborative roles, rather than the COD/TN ratio. Furthermore, TN removal was very significantly positively correlated with voltage and the relative abundance of Rhodanobacter. In summary, this study provided an insight for the key functional genes shaping the enhanced nitrogen removal by the newly designed TFCW-MFC system.

A newly combined dewatered alum sludge (DAS) and neutralized used acid (NUA) biofilter has been constructed and investigated recently, aiming for improving nitrate (NO3−–N) removal in simulated groundwater and exploring the spatiotemporal distribution of nirS and nosZ. The biofilter achieved 81.54% and 13.6 g N/ (m3 d) removal efficiency of NO3−–N during the stabilization period. Spatiotemporal distributions of diversity and composition of nirS and nosZ varied approximately in two media with depths and time. Both DAS and NUA played important roles in attenuating nitrate because of predominant denitrifying genera functions, and the core differences were Rhodanobacter and Rhodobacter in DAS while Halomonas, Pseudogulbenkiania, and Cupriavidus in NUA. Acting as the strongly correlated genera, Magnetospirillum and Halomonas had a significantly positive or negative correlation with other dominant genera. Positive correlations existed among COD, TN, NO3−−N, NO2−−N, and both nirS and nosZ in the DAS filter, whereas the correlations were negative in the NUA filter. Particularly, the effluent concentration of NO3−−N had a significantly negative correlation with the relative abundance of Rubrivivax and Pseudomonas. These results could be useful in adjusting the denitrification of nitrogen contaminants at the genetic level, especially in mitigating the influence of discharge of NO3−−N on the process of groundwater restoration.

This study systematically evaluated five microbial and four mitochondrial DNA (mtDNA) markers, including sensitivities and specificities under PCR method, and fecal concentrations and decay rates in water under qPCR method. The microbial DNA markers were the three human-associated (BacH, HF183 and B.adolescentis) and two pig-associated (Pig-2-Bac and L.amylovorus), while the mtDNA ones were two human- (H-ND6 and H-ND5) and two pig-associated (P-CytB and P-ND5). All the mtDNA markers showed higher sensitivity (100%) than the microbial ones (84.0–88.8%) except Pig-2-Bac (100%). Specificities of the human mtDNA markers (99.1 and 98.1%) were higher than those of the human-associated microbial ones (57.0–88.8%). But this pattern was not observed in the pig-associated markers where Pig-2-Bac had 100% specificity. The reliability of H-ND6 and H-ND5 was further evidenced to identify locations of the most polluted within the Taihu Lake watershed of China. In general, the microbial DNA markers demonstrated a higher fecal concentration than the mtDNA ones; increasing temperature and sunlight exposure accelerated significantly the decay of all the DNA markers. Results of this study suggest that DNA markers H-ND6, H-ND5, and Pig-2-Bac may be among the best for fecal source tracking in water.