Variations of nitrogen-metabolizing enzyme activity and microbial community under typical loading conditions in full-scale leachate anoxic/aerobic system

Simultaneous suppression of As mobilization and N2O emission from NH4+/As-rich paddy soils by combined nitrate and birnessite amendment

The environmental impacts of As mobilization and nitrous oxide (N2O) emission in flooded paddy soils are serious issues for food safety and agricultural greenhouse gas emissions. Several As immobilization strategies utilizing microbially-mediated nitrate reducing-As(III) oxidation (NRAO) and birnessite (δ-MnO2)-induced oxidation/adsorption have proven effective for mitigating As bioavailability in flooded paddy soils. However, several inefficiency and unsustainability issues still exist in these remediation approaches. In this study, the effects of a combined treatment of nitrate and birnessite were assessed for the simultaneous suppression of As(III) mobilization and N2O emission from flooded paddy soils. Microcosm incubations confirmed that the combined treatment achieved an effective suppression of As(III) mobilization and N2O emission, with virtually no As(T) released and at least a 87% decrease in N2O emission compared to nitrate treatment alone after incubating for 8 days. When nitrate and birnessite are co-amended to flooded paddy soils, the activities of denitrifying enzymes within the denitrification electron transport pathway were suppressed by MnO2. As a result, the majority of applied nitrate participated in nitrate-dependent microbial Mn(II) oxidation. The regenerated biogenetic MnO2 was available to facilitate subsequent cycles of As(III) immobilization and concomitant N2O emission suppression, sustainable remediation strategy. Moreover, the combined nitrate-birnessite amendment promoted the enrichment of Pseudomonas, Achromobacter and Cupriavidu, which are known to participate in the oxidation of As(III)/Mn(II). Our findings document strong efficacy for the combined nitrate/birnessite treatment as a remediation strategy to simultaneously mitigate As-pollution and N2O emission, thereby improving food safety and reducing greenhouse gas emissions from flooded paddy soils enriched with NH4+ and As.

Enhanced denitrification of the AO-MBBR system used for expressway service area sewage treatment: A new perspective on decentralized wastewater treatment

Decentralized wastewater treatment warrants considerable development in numerous countries and regions. Owing to the unique characteristics of high ammonia nitrogen concentrations and low carbon/nitrogen ratio, nitrogen removal is a key challenge in treating expressway service area sewage. In this study, an anoxic/oxic-moving bed biofilm reactor (A/O-MBBR) and a traditional A/O bioreactor were continuously operated for 115 days and their outcomes were compared to investigate the enhancement effect of carriers on the total nitrogen removal (TN) for expressway service area sewage. Results revealed that A/O-MBBR required lower dissolved oxygen, exhibited higher tolerance toward harsh conditions, and demonstrated better shock load resistance than traditional A/O bioreactor. The TN removal load of A/O-MBBR reached 181.5 g‧N/(m3‧d), which was 15.24% higher than that of the A/O bioreactor. Furthermore, under load shock resistance, the TN removal load of A/O-MBBR still reached 327.0 g‧N/(m3‧d), with a TN removal efficiency of above 80%. Moreover, kinetics demonstrated that the denitrification rate of the A/O-MBBR was 121.9% higher than that of the A/O bioreactor, with the anoxic tank biofilm contributing 60.9% of the total denitrification rate. Community analysis results revealed that the genera OLB8, uncultured_f_Saprospiraceae and OLB12 were the dominant in biofilm loaded on carriers, and OLB8 was the key for enhanced denitrification. FAPROTAX and PICRUSt2 analyses confirmed that more bacteria associated with nitrogen metabolism were enriched by the A/O-MBBR carriers through full denitrification metabolic pathway and dissimilatory nitrate reduction pathway. This study offers a perspective into the development of cost-effective and high-efficiency treatment solutions for expressway service area sewage.

Application fruit tree hole storage brick fertilizer is beneficial to increase the nitrogen utilization of grape under subsurface drip irrigation

It is very important to promote plant growth and decrease the nitrogen leaching in soil, to improve nitrogen (N) utilization efficiency. In this experiment, we designed a new fertilization strategy, fruit tree hole storage brick (FTHSB) application under subsurface drip irrigation, to characterise the effects of FTHSB addition on N absorption and utilization in grapes. Three treatments were set in this study, including subsurface drip irrigation (CK) control, fruit tree hole storage brick A (T1) treatment, and fruit tree hole storage brick B (T2) treatment. Results showed that the pore number and size of FTHSB A were significantly higher than FTHSB B. Compared with CK, T1 and T2 treatments significantly increased the biomass of different organs of grape, N utilization and 15N content in the roots, stems and leaves, along with more prominent promotion at T1 treatment. When the soil depth was 15-30 cm, the FTHSB application significantly increased the soil 15N content. But when the soil depth was 30-45 cm, it reduced the soil 15N content greatly. T1 and T2 treatments obviously increased the activities of nitrite reductase (NR) and glutamine synthetase (GS) in grape leaves, also the urease activity(UR) in 30 cm of soil. Our findings suggest that FTHSB promoted plant N utilization by reducing N loss in soil and increasing the enzyme activity related to nitrogen metabolism. In addition, this study showed that FTHSB A application was more effective than FTHSB B in improving nitrogen utilization in grapes.

Study on the chemical compositions and microbial communities of cigar tobacco leaves fermented with exogenous additive

Fermentation process plays an important role in the biochemical properties and quality of cigar tobacco leaves (CTLs). In industry, exogenous additive (EA) was usually adopted for improving the quality of CTLs during fermentation. However, the mechanism of enhanced quality of CTLs fermented with EA was confused. Herein, the chemical compositions and microbial communities of CTLs during fermentation with EA were analyzed. The increased contents of total nitrogen and total sugar, as well as the improved consumption rate of reducing sugar in CTLs were found with the addition of EA. Besides, fermentation with EA reduced the content of total nonvolatile organic acid, especially unsaturated fatty acid. The contents of total and several representative aroma components were improved. Additionally, the increased abundance of Staphylococcus and decreased abundance of Aspergillus were detected. Combined with the changes of chemical compositions and microbial communities, it was confirmed that the carbohydrates and alcohols originated from EA promote the enrichment of Staphylococcus and accelerate biochemical reactions, such as Maillard reaction and esterification reaction, thus improving the contents and quality of aroma components in CTLs. This study demonstrated the mechanism of enhanced quality of CTLs fermented by EA, which provides more ideas for developing novel and efficient EAs.