Search Results (24)

Urban development and intensive human activities have led to increasingly prominent nitrogen pollution issues in the Baiyangdian Lake basin. Accurately identifying the sources of nitrate pollution is a crucial prerequisite for implementing targeted remediation strategies, while flooding further complicates this task by exacerbating the transport and mixing of multi-source pollutants within the basin. This study, conducted from August to October 2023 (encompassing flood and post-flood periods), established 20 sampling sites in the lake area and its major inflow rivers. By integrating hydrochemical parameters, nitrate dual-isotope tracers (δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻), and the Bayesian mixing model (MixSIAR), we quantitatively revealed the contributions of nitrate sources and their response mechanisms to a major flood event. The results indicate that domestic sewage and livestock wastewater (Manure & Sewage, MS) were the dominant sources of nitrate, with an average contribution of 84.0%, which further increased to 90.3% after the flood. Soil nitrogen was a secondary source (average 12.3%), while contributions from chemical fertilizers and atmospheric deposition were negligible (<4%). The results quantified a flood-driven dynamic response process of the nitrate source structure, characterized by “dilution-mixing-pollution rebound-process transformation”: the initial flood stage (August) showed multi-source mixing; the post-flood period (September) witnessed a rapid rebound of sewage sources; and during the October, nitrification persisted, but the basin’s overall denitrification capacity was limited, indicating a risk of nitrogen accumulation. Spatially, rivers like the Fu River were identified as key input pathways. This study revises the traditional understanding by emphasizing the absolute dominance of sewage sources after extreme hydrological events and the risk of insufficient denitrification capacity. The findings provide a scientific basis for water quality management in Baiyangdian and similar lakes. Full article

Although tropical ecosystems have become increasingly vulnerable to fire over the past century, the mechanisms by which fire disturbance influences N₂O emissions in these regions remain poorly understood. This study investigated the effects of fire on nitrous oxide (N₂O) emissions, the gross nitrification rate (GN), denitrification genes, and carbon (C) and nitrogen (N) fractions in a tropical forest. The results showed that fire increased the GN by 41.5%. The abundance of the nirK and nirS genes encoding nitrite reductase increased by 16.3% and 27.5%, respectively, while the abundance of the nosZI gene encoding N₂O reductase increased by 28%, suggesting a potentially enhanced denitrification capacity. This enhancement in nitrification and denitrification was mainly due to increased easily oxidizable organic C (EOC, +35%), light fraction organic C (LFOC, +32%), hydrolyzable ammonium N (HAN, +13%), and amino sugar N (ASN, +11%), which provided additional substrates for nitrification and denitrification. As a result, soil N₂O emissions increased by 18% in response to fire. Soil N₂O emissions showed a significant and positive linear correlation with GN, EOC, LFOC, HAN, nirK, nirS, and nosZI. Thus, the post-fire increase in N₂O emissions is likely driven by enhanced nitrification and denitrification processes, facilitated by the elevated availability of labile C and N fractions. Our findings provide new evidence for the role of soil C and N fractions in controlling N₂O emission and nitrification–denitrification under fire disturbances in tropical soils. Full article

The post-combustion technology of circulating fluidized beds (CFBs) can largely reduce the emission of nitrogen oxides (NO_x) in the process of combustion, significantly reducing the removal cost of NO_x. To explore the potential of the combined removal of NO_x and SO₂ emissions under post-combustion technology, experiments were conducted on a 0.1 MWth circulating fluidized bed test platform. This paper focuses on the effect of temperature in CFB with limestone addition on NO_x and SO₂ emissions under post-combustion technology combined with sorbent injection into the furnace. The low-cost combined removal of NO_x and SO₂ can be realized by denitrification in the furnace and through secondary desulfurization in the furnace and post-combustion chamber. In the optimized experimental condition, with combustion temperatures at 845 °C and sorbent addition in the furnace under post-combustion, the emission of NO_x can be reduced to 47.10 mg/Nm³(@6%O₂), and meanwhile, the emission of SO₂ can be reduced to 92.09 mg/Nm³. Sulfur removal efficiency is higher under lower temperatures in a weakly reducing atmosphere. The reaction of sulfur fixation occurred in the post-combustion chamber and caused the particle size of fly ashes at the tail flue to become bigger and the sulfur content in the fly ash at the tail flue to increase. At 845–905 °C, the combustion temperature had a bigger effect on the SO₂ emission than the NO_x with sorbent addition in the furnace under post-combustion. Full article

The construction of an anaerobic digester coupled with post-digestion low-level aeration for agricultural wastewater treatment is described. The digester employs underwater speakers to accelerate the anaerobic digestion process while retaining solids to reduce the strength of the effluent. The effluent is sent to a holding tank and fed at a low flow rate to an aeration tank to effect partial nitrification of the wastewater. The outlet of this tank is sent to a settling tank to retain biomass that developed in the aeration tank, and the effluent is sent to a small constructed wetland to further reduce wastewater nitrogen and phosphorus. The wetland was planted with the broadleaf cattail, Typha latifolia, and hence led to the formation of a retention basin. The system has reduced energy consumption due to the use of underwater sonic treatment and low-level aeration that is not designed to achieve full nitrification/denitrification but rather to achieve a mixture of ammonium, nitrite, and nitrate that might foster the development of a consortium of organisms (i.e., nitrifiers and Anammox bacteria) that can remediate wastewater ammonium at low cost. The system is meant to serve as a complex where various technologies and practices can be evaluated to improve the treatment of agricultural wastewater. Preliminary data from the system are presented. Full article

Background/Objectives: Chemical fumigation can effectively inhibit the occurrence of soil-borne diseases; however, this approach can negatively affect the structure of the soil microbial community. The combination of soil fumigant and organic fertilizer application thus represents a widely adopted strategy in agricultural practice. Traditional Chinese medicine residue (TCMR) is a high-quality organic fertilizer; however, the impact of post-fumigation TCMR application on keystone taxa and their functional traits remains uncertain. Methods: This study examined the effects of five fertilization treatments on the diversity, key species, and related functional genes of microbial communities in rhizosphere soil of continuous cropping pepper. Results: Chemical fumigation followed by TCMR application markedly enhanced soil nutrient content in the rhizosphere and significantly influenced microbial community composition as well as functional gene patterns associated with microbial nitrogen cycling. It was also strongly correlated with soil bioavailable nitrogen content. The abundance of keystone bacterial species (Pseudomonadota, Actinomycetota, and Bacillota) substantially increased following TCMR application, alongside a notable rise in Ascomycota abundance within the fungal community. This shift contributed to an increase in beneficial bacterial abundance while reducing that of harmful bacteria. Additionally, TCMR addition affected the abundance of denitrification and DNRA genes involved in nitrogen cycling; specifically, nirB and nirK were strongly associated with soil organic nitrogen content. Conclusions: The combined application of chemical fumigants and TCMR modified the composition of keystone microbial community species by influencing rhizosphere soil TN and other nutrients, and these alterations were linked to multiple nitrogen-cycling functional genes. Full article

Pilot-scale experimental measurements and simulations were utilised to evaluate the nutrient removal efficiency of three submerged membrane bioreactor designs. This study compared setups with post- and pre-denitrification processes. A 625 L pilot plant for treating primary effluent provided the operational data necessary for calibrating the activated sludge model, specifically for chemical oxygen demand and nitrogen removal under steady-state flow. Identical influent conditions were maintained for all configurations while varying the sludge retention times (from 5 to 100 d), hydraulic retention times (ranging from 4 to 15 h), return activated sludge flow rates (between 0.1 and 3.0), and aerobic volume fractions (from 0.3 to 1.0). The pilot plant tests showed high COD and ammonia removal (above 90%) but moderate total nitrogen removal (above 70%). The simulation results successfully forecasted the effluent concentrations of COD and nitrogen for each configuration. There were noticeable variations in the kinetic parameters, such as mass transfer coefficients and biomass decay rates, related to the activated sludge model. However, increasing the sludge retention time beyond 20 d, hydraulic retention time beyond 8 h, return activated sludge rates above 2.0, or aerobic volume fractions beyond 0.4 did not significantly enhance nutrient removal. The post-denitrification setup showed a clear benefit in nitrogen removal but required a greater oxygen supply. Full article

To achieve the in situ capacity expansion of the post-denitrification biological aerated filter (BAF-DN), the integration of BAF with the anammox process (BAF/AX) was proposed. With the objective of maximizing retaining ammonia nitrogen, the operational optimization of BAF was achieved by two distinct strategies. The treatment performance of BAF demonstrated that the removal efficiencies of chemical oxygen demand (COD) and ammonia nitrogen (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$) was 66.3~67.3% and 4~12%, respectively, under conditions of low aeration intensity (0.4 m³·m⁻²·h⁻¹) or a shortened empty bed residence time (EBRT) of 30 min. Residual ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ in the BAF effluent served as the ammonia substrate for the subsequent anammox process, which was successfully launched by using ceramic particles and sponges as carriers. Notably, the sponge carrier facilitated a shorter start-up period of 41 to 44 days. Furthermore, the sponge-based anammox reactor exhibited a superior ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ removal capacity (≥85.7%), under operations of a shorter EBRT of 40 min, low influent ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ concentrations (≤30 mg/L), and COD levels of ≤67 mg/L. In addition, a comprehensive evaluation of the BAF/AX process was conducted, which considered performance, cost-effectiveness, and engineering feasibility. The performance results illustrated that the effluent quality met the standard well (with a COD level of ≤ 50 mg/L, and a TN of ≤3.1~10.5 mg/L). Following a comparison against the low aeration intensity operation, it was recommended to operate BAF at a low EBRT within the BAF/AX process. Consequently, the treated volume was double the volume of the standalone BAF-DN, synchronously achieving low costs (0.413 yuan/m³). Full article

Moving bed biofilm reactors (MBBRs) are compact biofilm systems that provide a sustainable solution for biological nitrogen removal. A study was conducted on an innovative post-denitrification method as a polishing step to reduce low nitrate nitrogen concentrations (10 mg/L) to 2.1–4.9 mg/L. The objective was to minimize residual chemical oxygen demand (COD) in the effluent caused by the external carbon source required for this final treatment step. Therefore, four continuous flow reactors with varying synthetic loads and hydraulic retention times (HRTs), as well as two carrier sizes, were operated over 335 days. The results showed that an HRT of 2 h is necessary to successfully reduce the residual COD to 5–6 mg/L. Additionally, it was demonstrated that the protected volume of the biofilm carriers has a significant impact on MBBRs compared to the protected surface, which is commonly discussed in the literature. The available protected volume can limit biofilm growth, as demonstrated by measuring the total biofilm solids (TBS) and biofilm thickness on the carrier at varying COD eliminations. When providing sufficient protected volume for the biofilm through the filling ratio and carrier size, a COD elimination rate of 1.4 to 1.45 kg/(m³d) was achieved with a biofilm thickness of only 500 µm. Full article

Nitrate contamination in groundwater is a global concern due to its widespread presence and consequential social, environmental, and economic ramifications. This study investigates the efficacy of biological denitrification in a humid tropical setting, utilizing corn cob in batch and column tests to assess nitrate removal under varying conditions. Batch tests demonstrated the nitrate removal efficiencies of 93.14%, 91.58%, 90.77%, and 98.74% for initial concentrations of 22.18 ± 2.82 mg/L, 27.3 mg/L, 69.1 ± 1.2 mg/L and 115.08 ± 1.88 mg/L, respectively. In the column test, the removal efficiency was 99.86%, 87.13%, and 74%, and the denitrification rate was 32.82, 53.43, and 83.53 mg NO₃⁻-N/L d, for a hydraulic retention time (HRT) of 24 h, 16 h, and 7 h, respectively. Predominantly, nitrate removal occurred via biological denitrification, particularly favoring a 24 h HRT. The corn cob effectively removed high nitrate concentrations of up to 115 mg NO₃⁻-N/L. Scanning electron microscopy and Fourier transform infrared spectroscopy revealed surface characteristic changes of the carbon source pre- and post-denitrification. This research sheds light on the potential of biological denitrification using corn cob in humid tropical environments, offering a promising avenue for addressing nitrate contamination challenges in groundwater systems. Full article

Conventionally, nitrification in biological nitrogen removal (BNR) requires high dissolved oxygen (DO) concentrations (>2 mg L⁻¹), making the process energy intensive. Recent studies have shown that efficient ammonium removal and energy reduction can be realized by operating the nitrification at low DO concentrations (<1 mg L⁻¹). In this study, the low-DO oxic anoxic (low-DO OA) process was operated in a pilot-scale sequencing batch reactor (SBR) over 218 days to evaluate the feasibility of nitrogen removal from low chemical oxygen demand-to-nitrogen ratio (COD/N) tropical municipal wastewater. The results revealed that the low-DO OA process attained high removal efficiency for ammonium (97%) and total nitrogen (TN) (80%) under an average DO concentration of 0.6 mg L⁻¹. The effective TN removal efficiency is attributed to the occurrence of simultaneous nitrification–denitrification (SND) under low DO conditions. Further batch tests revealed that slowly biodegradable COD (sbCOD) in tropical wastewater can support denitrification in the post-anoxic phase, resulting in a high TN removal rate. Compared with high DO concentrations (2 mg L⁻¹), low DO conditions achieved 10% higher TN removal efficiency, with similar ammonium and COD removal efficiency. This study is crucial in promoting the energy efficiency and sustainability of wastewater treatment plants treating low COD/N wastewater. Full article

Supplementation of alternative carbon sources is a technological bottleneck, particularly in post-denitrification processes due to stringent effluent nitrogen levels. This study focuses on enhancing the sustainability of wastewater treatment practices by partially replacing conventionally used fossil-derived methanol with organic waste-derived volatile fatty acids (VFAs) in moving bed biofilm reactors (MBBRs). In this regards, results of denitrification batch assays with sequential or simultaneous addition of VFA effluent from acidogenic fermentation of potato starch residue (AD-VFA_PPL) and chicken manure (AD-VFA_CKM), simulated synthetic VFAs solutions (sVFAs), and methanol as carbon source were presented and discussed. Although methanol has proven superior in the conversion of nitrate to nitrite, VFAs are more effective when it comes to reducing nitrite. Although solely added AD-VFA_PPL had a slower denitrification capability (0.56 ± 0.13 mgNO_x-N removed/m²/day) than methanol (1.04 ± 0.46 mgNO_x-N removed/m²/day), up to 50% of the methanol can be replaced by waste-derived AD-VFA_PPL and achieve comparable performance (1.08 ± 0.07 mgNO_x-N removed/m²/day) with the pure methanol. This proves that the co-addition of VFAs together with methanol can fully compete with pure methanol in performance, providing a promising opportunity for wastewater treatment plants to potentially reduce their carbon footprint and become more sustainable in practice while benefiting from recovered nutrients from waste. Full article

Nitrogen oxide (NOx) is a major gaseous pollutant in flue gases from power plants, industrial processes, and waste incineration that can have adverse impacts on the environment and human health. Many denitrification (de-NOx) technologies have been developed to reduce NOx emissions in the past several decades. This paper provides a review of the recent literature on NOx post-combustion purification methods with different reagents. From the perspective of changes in the valence of nitrogen (N), purification technologies against NOx in flue gas are classified into three approaches: oxidation, reduction, and adsorption/absorption. The removal processes, mechanisms, and influencing factors of each method are systematically reviewed. In addition, the main challenges and potential breakthroughs of each method are discussed in detail and possible directions for future research activities are proposed. This review provides a fundamental and systematic understanding of the mechanisms of denitrification from flue gas and can help researchers select high-performance and cost-effective methods. Full article

Aspergillus fumigatus is the leading cause of the fungal invasive disease called aspergillosis, which is associated with a high mortality rate that can reach 50% in some groups of immunocompromised individuals. The increasing prevalence of azole-resistant A. fumigatus isolates, both in clinical settings and the environment, highlights the importance of discovering new fungal virulence factors that can potentially become targets for novel antifungals. Nitronate monooxygenases (Nmos) represent potential targets for antifungal compounds as no orthologs of those enzymes are present in humans. Nmos catalyse the denitrification of nitroalkanes, thereby detoxifying these mediators of nitro-oxidative stress, and therefore we tested whether Nmos provide protection for A. fumigatus against host-imposed stresses at sites of infection. The results of inhibition zone assays indicated that Nmo2 and Nmo5 are not essential for the oxidative stress resistance of A. fumigatus in vitro. In addition, the resazurin-based metabolic activity assay revealed that the growth of mutants lacking the nmo2 or nmo5 genes was only slightly reduced in the presence of 0.05 mM peroxynitrite. Nevertheless, both Nmo2 and Nmo5 were shown to contribute to defense against murine bone marrow-derived macrophages, and this was no longer observed when NADPH oxidase, the main generator of reactive oxygen species during infection, was inhibited in macrophages. Furthermore, we revealed that Nnmos promote the virulence of the fungus in the Galleria mellonella model of infection. Both nmo2 and nmo5 knock-out strains were less virulent than the wild-type control as recorded 72 h post-infection. Our results indicate that Nmos play a role in the virulence of A. fumigatus. Full article

Nitrous oxide (N₂O) is a powerful greenhouse gas that contributes to climate change. Denitrification is one of the largest sources of N₂O in soils. The soybean endosymbiont Bradyrhizobium diazoefficiens is a model for rhizobial denitrification studies since, in addition to fixing N₂, it has the ability to grow anaerobically under free-living conditions by reducing nitrate from the medium through the complete denitrification pathway. This bacterium contains a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a c-type nitric oxide reductase (cNor), and a Cu-dependent nitrous oxide reductase (Nos) encoded by the napEDABC, nirK, norCBQD and nosRZDFYLX genes, respectively. In this work, an integrated study of the role of Cu in B. diazoefficiens denitrification has been performed. A notable reduction in nirK, nor, and nos gene expression observed under Cu limitation was correlated with a significant decrease in NirK, NorC and NosZ protein levels and activities. Meanwhile, nap expression was not affected by Cu, but a remarkable depletion in Nap activity was found, presumably due to an inhibitory effect of nitrite accumulated under Cu-limiting conditions. Interestingly, a post-transcriptional regulation by increasing Nap and NirK activities, as well as NorC and NosZ protein levels, was observed in response to high Cu. Our results demonstrate, for the first time, the role of Cu in transcriptional and post-transcriptional control of B. diazoefficiens denitrification. Thus, this study will contribute by proposing useful strategies for reducing N₂O emissions from agricultural soils. Full article

Root selection of their associated microbiome composition and activities is determined by the plant’s developmental stage and distance from the root. Total gene abundance, structure and functions of root-associated and rhizospheric microbiomes were studied throughout wheat growth season under field conditions. On the root surface, abundance of the well-known wheat colonizers Proteobacteria and Actinobacteria decreased and increased, respectively, during spike formation, whereas abundance of Bacteroidetes was independent of spike formation. Metagenomic analysis combined with functional co-occurrence networks revealed a significant impact of plant developmental stage on its microbiome during the transition from vegetative growth to spike formation. For example, gene functions related to biofilm and sensorial movement, antibiotic production and resistance and carbons and amino acids and their transporters. Genes associated with these functions were also in higher abundance in root vs. the rhizosphere microbiome. We propose that abundance of transporter-encoding genes related to carbon and amino acid, may mirror the availability and utilization of root exudates. Genes related to antibiotic resistance mechanisms were abundant during vegetative growth, while after spike formation, genes related to the biosynthesis of various antibiotics were enriched. This observation suggests that during root colonization and biofilm formation, bacteria cope with competitor’s antibiotics, whereas in the mature biofilm stage, they invest in inhibiting new colonizers. Additionally, there is higher abundance of genes related to denitrification in rhizosphere compared to root-associated microbiome during wheat growth, possibly due to competition with the plant over nitrogen in the root vicinity. We demonstrated functional and phylogenetic division in wheat root zone microbiome in both time and space: pre- and post-spike formation, and root-associated vs. rhizospheric niches. These findings shed light on the dynamics of plant–microbe and microbe–microbe interactions in the developing root zone. Full article