Effects of the three amendments on NH3 volatilization, N2O emissions, and nitrification at four salinity levels: An indoor experiment.

The marked salinity and alkaline pH of coastal saline soil profoundly impact the nitrogen conversion process, leading to a significantly reduced nitrogen utilization efficiency and substantial gaseous nitrogen loss. The application of soil amendments (e.g. biochar, manure, and gypsum) was proved to be effective for the remediation of saline soils. However, the effects of the three amendments on soil nitrogen transformation in soils with various salinity levels, especially on NH3 volatilization and N2O emission, remain elusive. Here, we reported the effects of biochar, manure, and gypsum on NH3 volatilization and N2O emission under four natural salinity gradients in the Yellow River Delta. Also, high-throughput sequencing and qPCR analysis were performed to characterize the response of nitrification (amoA) and denitrification (nirS, nirK, and nosZ) functional genes to the three amendments. The results showed that the three amendments had little effect on NH3 volatilization in low- and moderate-salinity soils, while biochar stimulated NH3 volatilization in high-salinity soils and reduced NH3 volatilization in severe-salinity soils. Spearman correlation analysis demonstrated that AOA was significantly and positively correlated with the NO3--N content (r = 0.137, P < 0.05) and N2O emissions (r = 0.174, P < 0.01), which indicated that AOA dominated N2O emissions from nitrification in saline soils. Structural equation modeling indicated that biochar, manure, and gypsum affected N2O emission by influencing soil pH, conductivity, mineral nitrogen content, and functional genes (AOA-amoA and nosZ). Two-way ANOVA further showed that salinity and amendments (biochar, manure, and gypsum) had significant effects on N2O emissions. In summary, this study provides valuable insights to better understand the effects of gaseous N changes in saline soils, thereby improving the accuracy and validity of future GHG emission predictions and modeling.

The Microbiome and Antibiotic Resistome in Soil under Biodegradable Composite Carbon Source Amendment.

The decomposition of biodegradable composite carbon sources generates a large amount of biodegradable microplastics, which may not only furnish microbial denitrification, but might also pose potential environmental risks. In the present study, the effects of different dosages of a biodegradable composite carbon source on the microbial communities, the nitrogen metabolic pathways and the antibiotic resistome were explored through Illumina MiSeq sequencing analysis and metagenomic analysis. The results of partial least-square discriminant analysis (PLS-DA) and analysis of similarity (ANOSIM) demonstrated that the response of the bacterial community to a biodegradable composite carbon source was more obvious than the fungal community. The application of biodegradable microplastics diminished the complexity of the microbial communities to some extent and obviously stimulated denitrification. Antibiotics resistance gene (ARG) dispersal was not evidently accelerated after the addition of biodegradable composite carbon source. Lysobacter, Methylobacillus, Phyllobacterium, Sinorhizobium, Sphingomonas from Proteobacteria and Actinomadura, Agromyces, Gaiella and Micromonospora from Actinobacteria were the major ARG hosts. Overall, the addition of a biodegradable composite carbon source shaped microbial communities and their antibiotic resistance profiles in this study.

Reinforced Bioremediation of Excessive Nitrate in Atrazine-Contaminated Soil by Biodegradable Composite Carbon Source.

Bioremediation is a good alternative to dispose of the excessive nitrate (NO3-) in soil and alleviate the secondary salinization of soil, but the presence of atrazine in soil interferes with the bioremediation process. In the present study, the biodegradable composite carbon source with different dosages was added to the atrazine-contaminated soil to intensify the bioremediation of excessive NO3-. The atrazine-contaminated soil with a 25 g/kg composite carbon source achieved the optimal NO3- removal performance (92.10%), which was slightly higher than that with a 5 g/kg composite carbon source (86.15%) (p > 0.05). Unfortunately, the negative effects of the former were observed, such as the distinctly higher emissions of N2O, CO2 and a more powerful global warming potential (GWP). Microbial community analysis showed that the usage of the composite carbon source clearly decreased the richness and diversity of the microbial community, and greatly stimulated nitrogen metabolism and atrazine degradation (p < 0.05). To sum up, the application of a 5 g/kg composite carbon source contributed to guaranteeing bioremediation performance and reducing adverse environmental impacts at the same time.

Improved Denitrification Performance of Polybutylene Succinate/Corncob Composite Carbon Source by Proper Pretreatment: Performance, Functional Genes and Microbial Community Structure.

Blending biodegradable polymers with plant materials is an effective method to improve the biodegradability of solid carbon sources and save denitrification costs, but the recalcitrant lignin in plant materials hinders the microbial decomposition of available carbon sources. In the present study, corncob pretreated by different methods was used to prepare polybutylene succinate/corncob (PBS/corncob) composites for biological denitrification. The PBS/corncob composite with alkaline pretreatment achieved the optimal NO3--N removal rate (0.13 kg NO3--N m-3 day-1) with less adverse effects. The pretreatment degree, temperature, and their interaction distinctly impacted the nitrogen removal performance and dissolved organic carbon (DOC) release, while the N2O emission was mainly affected by the temperature and the interaction of temperature and pretreatment degree. Microbial community analysis showed that the bacterial community was responsible for both denitrification and lignocellulose degradation, while the fungal community was primarily in charge of lignocellulose degradation. The outcomes of this study provide an effective strategy for improving the denitrification performance of composite carbon sources.

Metagenomic analyses of microbial structure and metabolic pathway in solid-phase denitrification systems for advanced nitrogen removal of wastewater treatment plant effluent: A pilot-scale study.

The pilot-scale solid-phase denitrification systems supporting with poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PHBV) and PHBV-sawdust were constructed for advanced nitrogen removal from wastewater treatment plants (WWTPs) effluent, and the impacts of biomass blended carbon source on microbial community structure, functions and metabolic pathways were analyzed by metagenomic sequencing. PHBV-sawdust system achieved the optimal denitrification performance with higher NO3--N removal efficiency (96.58%), less DOC release (9.00 ± 4.16 mg L - 1) and NH4+-N accumulation (0.37 ± 0.32 mg L - 1) than PHBV system. Metagenomic analyses verified the significant differences in the structure of microbial community between systems and the presence of four anaerobic anammox bacteria. Compared with PHBV, the utilization of PHBV-sawdust declined the relative abundance of genes encoding enzymes for NH4+-N generation and increased the relative abundance of genes encoding enzymes involved in anammox, which contributed to the reduction of NH4+-N in effluent. What's more, the encoding gene for electrons generation in glycolysis metabolism obtained higher relative abundance in PHBV-sawdust system. A variety of lignocellulase encoding genes were significantly enriched in PHBV-sawdust system, which guaranteed the stable carbon supply and continuous operation of system. The results of this study are expected to provide theoretical basis and data support for the promotion of solid-phase denitrification.

Intensified simultaneous nitrification and denitrification performance in integrated packed bed bioreactors using PHBV with different dosing methods.

To explore an effective approach of simultaneous nitrification and denitrification in wastewater with low C/N ratios, integrated packed bed bioreactors based on poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) with different dosing methods were designed. The removal efficiency of NH4+-N in bioreactor with aeration was 88.62%, and higher NO3--N removal efficiency was observed in bioreactor filled with grainy PHBV (95.21%) than bioreactor filled with strip PHBV (93.34%). Microbial study indicated that microbes harboring amoA and nirS genes preferred to attach on the surface of ceramsite, and significant differences in microbial community compositions at phylum and genus levels were observed. To summarize, it is feasible to utilize grainy PHBV for simultaneous and efficient removal of NH4+-N and NO3--N from wastewater with low C/N ratios.

Nitrogen removal performance in pilot-scale solid-phase denitrification systems using novel biodegradable blends for treatment of waste water treatment plants effluent.

In this study, three pilot-scale solid-phase denitrification (SPD) systems filled with poly-3-hydroxybutyrate-co-hyroxyvelate (PHBV), PHBV-Rice hulls (PHBV-RH) and PHBV-Sawdust (PHBV-S) were operated to treat effluent of waste water treatment pangts (WWTPs). The fast start-up and intensified nitrogen removal performance were obtained in PHBV-RH and PHBV-S systems. Besides, the optimal total nitrogen (TN) removal efficiency was obtained in PHBV-S system (91.65 ± 4.12%) with less ammonia accumulation and dissolved organic carbon (DOC) release. The significant enrichment of amx 16S rRNA and nirS genes in PHBV-RH and PHBV-S systems indicated the possible coexistence of anammox and denitrification. Miseq sequencing analysis exhibited more complex community diversity, more abundant denitrifying and fermenting bacteria in PHBV-RH and PHBV-S systems. The co-existence of denitrification and anammox might contribute to better control of nitrogen and dissolved organic carbon in PHBV-S system. The outcomes provide an economical and eco-friendly alternative to improve nitrogen removal of WWTPs effluent.

Simultaneous removal of nitrogen and pharmaceutical and personal care products from the effluent of waste water treatment plants using aerated solid-phase denitrification system.

Nowadays, waste water treatment plants (WWTPs) are regarded as the pollution sources of nitrogen and pharmaceutical and personal care products (PPCPs). In the present study, the simultaneous removal of nitrogen and typical PPCPs, ibuprofen and triclosan, was evaluated in a poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) based solid-phase denitrification (SPD) system. Results after 602 days showed that simultaneous nitrification and denitrification (SND) process occurred with average 83.85 ±â€¯13.09% NH4+-N and 93.88 ±â€¯10.19% NO3--N removals in the SPD system. Interestingly, the system achieved average 79.69 ±â€¯6.35% and 65.96 ±â€¯7.62% removals of ibuprofen and triclosan, respectively, under stable influent conditions of 50 µg L-1. Cometabolic activities of heterotrophic denitrifying bacteria and ammonia oxidizing bacteria (AOB) probably played a role in the biodegradation of the two PPCPs. Illumina MiSeq sequencing results revealed that microbial composition enhanced the simultaneous removal of nitrogen and PPCPs in the SPD system.

Nitrogen removal performance and functional genes distribution patterns in solid-phase denitrification sub-surface constructed wetland with micro aeration.

An up-flow vertical flow constructed wetland (AC-VFCW) filled with ceramsite and 5% external carbon source poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) as substrate was set for nitrogen removal with micro aeration. Simultaneous nitrification and denitrification process was observed with 90.4% NH4+-N and 92.1% TN removal efficiencies. Nitrification and denitrification genes were both preferentially enriched on the surface of PHBV. Nitrogen transformation along the flow direction showed that NH4+-N was oxidized to NO3--N at the lowermost 10 cm of the substrate and NO3--N gradually degraded over the depth. AmoA gene was more enriched at -10 and -50 cm layers. NirS gene was the dominant functional gene at the bottom layer with the abundance of 2.05 × 107 copies g-1 substrate while nosZ gene was predominantly abundant with 7.51 × 106 and 2.64 × 106 copies g-1 substrate at the middle and top layer, respectively, indicating that functional division of dominant nitrogen functional genes forms along the flow direction in AC-VFCW.

Enhanced nitrogen removal using solid carbon source in constructed wetland with limited aeration.

In this study, the performances of nitrogen removal in constructed wetlands using solid carbon source with limited aeration were investigated. The blends of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) and polyacetic acid (PLA) were used as the carbon source and biofilm support. The performances of nitrogen removal, microbial abundance and microbial community structure in the biofilm attached on PHBV/PLA were investigated. Higher ammonia removal efficiency (91.00%) and total nitrogen removal efficiency (97.03%) than non-aerated constructed wetland (System NA) were achieved in constructed wetland with limited aeration (System A). The limited aeration decreased the average concentrations of COD in effluent. And, System A had higher microbial abundance than System NA. Pyrosequencing analysis showed that denitrifying bacteria Brevinema (41.85%) and Thiothrix (12.33%) were the predominant genus in the biofilm attached on the carbon source in System NA and System A, respectively.

Microbial abundance and community in subsurface flow constructed wetland microcosms: role of plant presence.

In this research, the role of plants in improving microorganism growth conditions in subsurface flow constructed wetland (CW) microcosms was determined. In particular, microbial abundance and community were investigated during summer and winter in Phragmites australis-planted CW microcosms (PA) and unplanted CW microcosms (control, CT). Results revealed that the removal efficiencies of pollutants and microbial community structure varied in winter with variable microbial abundance. During summer, PA comprised more dominant phyla (e.g., Proteobacteria, Actinobacteria, and Bacteroidetes), whereas CT contained more Cyanobacteria and photosynthetic bacteria. During winter, the abundance of Proteobacteria was >40 % in PA but dramatically decreased in CT. Moreover, Cyanobacteria and photosynthetic bacterial dominance in CT decreased. In both seasons, bacteria were more abundant in root surfaces than in sand. Plant presence positively affected microbial abundance and community. The potential removal ability of CT, in which Cyanobacteria and photosynthetic bacteria were abundant during summer, was more significantly affected by temperature reduction than that of PA with plant presence.