Search Results (13)

Municipal solid waste incineration generates by-products like nitrogen oxides, sulfur dioxide, and hydrogen chloride, contributing to environmental issues such as acid rain, ozone depletion, and photochemical smog. While industrial sites use desulfurization and denitrification to reduce emissions, no studies have modeled the formation mechanisms and influencing factors of these pollutants from a pollution reduction perspective. This study first analyzes the municipal solid waste incineration process to identify the main factors affecting the concentration of pollutants related to desulfurization and denitrification. A coupled numerical simulation model for the whole life cycle desulfurization and denitrification process in real municipal solid waste incineration power plants is then constructed using a method that couples two software tools. Next, based on a double orthogonal experimental design, virtual simulation data are generated using the numerical simulation model. Finally, an improved interval type-II fuzzy broad learning algorithm is applied to construct a mechanism model for the whole process of desulfurization and denitrification-related pollutant concentration, using the obtained virtual simulated data. Using a Beijing incineration plant as a case study, the whole life cycle model is successfully established. The research provides data for optimizing pollutant reduction, examines influencing factors, and lays the groundwork for future intelligent control. Full article

A novel species of the genus Methylocystis is proposed based on polyphasic evidence from strain SC2^T, isolated from the heavily polluted Saale River near Wichmar, Germany. Digital DNA–DNA hybridization and phylogenomic analyses demonstrate that strain SC2^T represents a distinct species within the genus, clearly separated from its closest relatives, namely Methylocystis suflitae NLS-7^T, Methylocystis rosea SV97^T, Methylocystis silviterrae FS^T, and Methylocystis hirsuta CSC1^T. As is typical of the family Methylocystaceae, cells possess intracytoplasmic membranes arranged parallel to the cytoplasmic membrane, and the dominant fatty acids are C18:1ω8c and C18:1ω7c. The strain grows aerobically on methane as the primary carbon and energy source and expresses both low- and high-affinity particulate methane monooxygenase (pMMO), but lacks the soluble form. The species epithet reflects the strain’s ability to utilize hydrogen as an alternative energy source. A further feature is its use of asparagine as an osmoprotectant, enhancing salt tolerance. Genomic analysis reveals complete pathways for nitrogen fixation, denitrification, and hydrogen oxidation. These genetic and physiological characteristics support the designation of a novel species, for which the name Methylocystis hydrogenophila sp. nov. is proposed. The type strain is SC2^T (=DSM 114506 = NCIMB 15437). Full article

In response to increasingly stringent emission regulations, low-carbon fuels have received significant attention as sustainable energy sources for internal combustion engines. This study investigates four representative low-carbon fuels, methane, methanol, hydrogen, and ammonia, by systematically summarizing their combustion characteristics and emission profiles, along with a review of existing after-treatment technologies tailored to each fuel type. For methane engines, unburned hydrocarbon (UHC) produced during low-temperature combustion exhibits poor oxidation reactivity, necessitating integration of oxidation strategies such as diesel oxidation catalyst (DOC), particulate oxidation catalyst (POC), ozone-assisted oxidation, and zoned catalyst coatings to improve purification efficiency. Methanol combustion under low-temperature conditions tends to produce formaldehyde and other UHCs. Due to the lack of dedicated after-treatment systems, pollutant control currently relies on general-purpose catalysts such as three-way catalyst (TWC), DOC, and POC. Although hydrogen combustion is carbon-free, its high combustion temperature often leads to elevated nitrogen oxide (NO_x) emissions, requiring a combination of optimized hydrogen supply strategies and selective catalytic reduction (SCR)-based denitrification systems. Similarly, while ammonia offers carbon-free combustion and benefits from easier storage and transportation, its practical application is hindered by several challenges, including low ignitability, high toxicity, and notable NO_x emissions compared to conventional fuels. Current exhaust treatment for ammonia-fueled engines primarily depends on SCR, selective catalytic reduction-coated diesel particulate filter (SDPF). Emerging NO_x purification technologies, such as integrated NO_x reduction via hydrogen or ammonia fuel utilization, still face challenges of stability and narrow effective temperatures. Full article

Molecular hydrogen (H₂) is crucial for agricultural microbial systems. However, the mechanisms underlying its influence on crop yields is yet to be fully elucidated. This study observed that H₂-based irrigation significantly increased strawberry (Fragaria × ananassa Duch.) yield with/without nutrient fertilization. The reduction in soil available nitrogen (N), phosphorus (P), potassium (K), and organic matter was consistent with the increased expression levels of N/P/K-absorption-related genes in root tissues at the fruiting stage. Metagenomics profiling showed the alterations in rhizosphere microbial community composition achieved by H₂, particularly under the conditions without fertilizers. These included the enrichment of plant-growth-promoting rhizobacteria, such as Burkholderia, Pseudomonas, and Cupriavidus genera. Rhizobacteria with the capability to oxidize H₂ (group 2a [NiFe] hydrogenase) were also enriched. Consistently, genes related to soil carbon (C) fixation (i.e., rbcL, porD, frdAB, etc.), dissimilar nitrate reduction (i.e., napAB and nrfAH), and P solublization, mineralization, and transportation (i.e., ppx-gppA, appA, and ugpABCE) exhibited higher abundance. Contrary tendencies were observed in the soil C degradation and N denitrification genes. Together, these results clearly indicate that microbe-mediated soil C, N, and P cycles might be functionally altered by H₂, thus increasing plant nutrient uptake capacity and horticultural crop yield. Full article

Due to low sludge production and being a clean source without residuals, hydrogen-based autotrophic denitrification appears to be a promising choice for nitrate removal from agricultural drainage waters or water/wastewater with a similar composition. Although the incorporation of hydrogen-based autotrophic denitrification with membrane bioreactors (MBRs) enabled almost 100% utilization of hydrogen, the technology still needs to be improved to better utilize its advantages. This study investigated the anoxic treatment of both synthetic and real drainage waters using hydrogen gas in a recently developed membrane bioreactor configuration, a venturi-integrated submerged membrane bioreactor, for the first time. The study examined the effects of the inflow nitrate concentration, and the use of a venturi device on the removal efficiency, as well as the effects of the presence of headspace gas circulation and circulation rate on membrane fouling. The study found that using the headspace gas circulation through a venturi device did not significantly affect the treatment efficiency, and in both cases, a removal efficiency of over 90% was achieved. When the inlet $N{O}_3^{-}–N$ concentration was increased from 50 mg/L to 100 mg/L, the maximum removal efficiency decreased from 98% to 92%. It was observed that the most significant effect of the headspace gas circulation was on the membrane fouling. When the headspace gas was not circulated, the average membrane chemical washing period was 5 days. However, with headspace gas circulation, the membrane washing period increased to an average of 12 days. The study found that the headspace gas circulation method significantly affected membrane fouling. When the upper phase was circulated with a peristaltic pump instead of a venturi device, the membrane washing period decreased to one day. The study calculated the maximum hydrogen utilization efficiency to be approximately 96%. Full article

In this study, a hydrogen-based denitrification (HD) reactor was used to investigate the simultaneous treatment of nitrogen and decolorization in textile wastewater contaminated with organic matter. The reactor operated in two phases: without and with organic matter. Despite the short hydraulic retention time, the HD system successfully removed all pollutants, including nitrate, nitrite, reactive black-5 dye and chemical oxygen demand. The unhindered treatment efficiency for nitrogen and decolorization in the presence of organic pollutants was observed. With the addition of organic matter, the nitrogen removal efficiency increased slightly from 85% to 90–100%, and the decolorization rate doubled from 25% to 50–60%. Organic matter played a crucial role in stimulating heterotrophic bacteria during biological denitrification and acted as a carbon source facilitating biological denitrification and azo bond cleavage during dye degradation. Despite the generation of toxic byproducts and changes in the dominant microbial community, the treatment efficiency remained stable and improved. This approach offers a promising solution for enhancing treatment efficiency in textile wastewater, providing a cost-effective and environmentally friendly option for developing countries to treat wastewater before discharge. Full article

Nitrite accumulation in hydrogen-based denitrification (HD) has been reported as a difficulty for achieving complete denitrification. Thauera sp. has been found as the dominant bacterial species in HD previously when using a plentiful amount of HCO₃⁻. This present study was successful in isolating Pseudomonas sp., Dietzia sp., Pannonibacter sp., Halomonas sp., Bacillus sp., and Thauera sp. These isolated strains were selected for investigating the nitrogen removal performance under the plentiful HCO₃⁻ condition. Only Pseudomonas sp. and Thauera sp. were capable of removing NO₂⁻ where the specific NO₂⁻ removal rate of Thauera sp. (36.02 ± 5.66 mgN gVSS⁻¹ day⁻¹) was 9 times quicker than that of Pseudomonas sp. (3.94 ± 0.80 mgN gVSS⁻¹ day⁻¹). The Thauera sp. strain was then tested at different HCO₃⁻ amounts. As a result, Thauera sp. had no ability to function both NO₃⁻ and NO₂⁻ removals under HCO₃⁻ deficit condition. This study provided evidence on the role of Thauera sp. and the necessity of bicarbonate in the hydrogen-based denitrification process to enhance its efficiency and to simultaneously reduce the operational cost especially for hydrogen. Full article

Partial denitrification, the termination of NO₃⁻-N reduction at nitrite (NO₂⁻-N), has received growing interest for treating wastewaters with high ammonium concentrations, because it can be coupled to anammox for total-nitrogen removal. NO₂⁻ accumulation in the hydrogen (H₂)-based membrane biofilm reactor (MBfR) has rarely been studied, and the mechanisms behind its accumulation have not been defined. This study aimed at achieving the partial denitrification with H₂-based autotrophic reducing bacteria in a MBfR. Results showed that by increasing the NO₃⁻ loading, increasing the pH, and decreasing the inorganic-carbon concentration, a nitrite transformation rate higher than 68% was achieved. Community analysis indicated that Thauera and Azoarcus became the dominant genera when partial denitrification was occurring. Functional genes abundances proved that partial denitrification to accumulate NO₂⁻ was correlated to increases of gene for the form I RuBisCo enzyme (cbbL). This study confirmed the feasibility of autotrophic partial denitrification formed in the MBfR, and revealed the inorganic carbon mechanism in MBfR denitrification. Full article

Low C/N wastewater results from a wide range of factors that significantly harm the environment. They include insufficient carbon sources, low denitrification efficiency, and ${\mathrm{NH}}_4^{+}$-N concentrations in low C/N wastewater that are too high to be treated. In this research, the membrane biofilm reactor and hydrogen-based membrane biofilm reactor (MBR-MBfR) were optimized and regulated under different operating parameters: the simulated domestic sewage with low C/N was domesticated and the domestic sewage was then denitrified. The results of the MBR-MBfR experiments indicated that a C/N ratio of two was suitable for ${\mathrm{NH}}_4^{+}$-N, ${\mathrm{NO}}_2^{-}$-N, ${\mathrm{NO}}_3^{-}$-N, and chemical oxygen demand (COD) removal in partial nitrification-denitrification (PN-D) and hydrogen autotrophic denitrification for further treatment. The steady state for domestic wastewater was reached when the MBR-MBfR in the experimental conditions of HRT = 15 h, SRT = 20 d, 0.04 Mpa for H₂ pressure in MBfR, 0.4–0.8 mg/L DO in MBR, MLSS = 2500 mg/L(MBR) and 2800 mg/L(MBfR), and effluent concentrations of ${\mathrm{NH}}_4^{+}$-N, ${\mathrm{NO}}_3^{-}$-N, and ${\mathrm{NO}}_2^{-}$-N were 4.3 ± 0.5, 1.95 ± 0.04, and 2.05 ± 0.15 mg/L, respectively. High-throughput sequencing results revealed the following: (1) The genus Nitrosomonas as the ammonia oxidizing bacteria (AOB) and Denitratisoma as potential denitrifiers were simultaneously enriched in the MBR; (2) at the genus level, Meiothermus,Lentimicrobium, Thauera,Hydrogenophaga, and Desulfotomaculum played a dominant role in leading to ${\mathrm{NO}}_3^{-}$-N and ${\mathrm{NO}}_2^{-}$-N removal in the MBfR. Full article

Textile wastewater (TW) contains toxic pollutants that pose both environmental and human health risks. Reportedly, some of these pollutants, including NO₃⁻_, NO₂⁻ and reactive black 5 (RB-5) dye, can be removed via hydrogen-based denitrification (HD); however, it is still unclear how different factors affect their simultaneous removal. This study aimed to investigate the effect of H₂ flow rate, the sparging cycle of air and H₂, and initial dye concentration on the TW treatment process. Thus, two reactors, an anaerobic HD reactor and a combined aerobic/anaerobic HD reactor, were used to investigate the treatment performance. The results obtained that increasing the H₂ flow rate in the anaerobic HD reactor increased nitrogen removal and decolorization removal rates. Further, increasing the time for anaerobic treatment significantly enhanced the pollutant removal rate in the combined reactor. Furthermore, an increase in initial dye concentration resulted in lower nitrogen removal rates. Additionally, some of the dye was decolorized during the HD process via bacterial degradation, and increasing the initial dye concentration resulted in a decrease in the decolorization rate. Bacterial communities, including Xanthomonadaceae, Rhodocyclaceae, and Thauera spp., are presented as the microbial species that play a key role in the mechanisms related to nitrogen removal and RB-5 decolorization under both HD conditions. However, both reactors showed similar treatment efficiencies; hence, based on these results, the use of a combined aerobic/anaerobic HD system should be used to reduce organic/inorganic pollutant contents in real textile wastewater before discharging is recommended. Full article

The back-diffusion of inactive gases severely inhibits the hydrogen (H₂) delivery rate of the close-end operated hydrogen-based membrane biofilm reactor (H₂-based MBfR). Nevertheless, less is known about the response of microbial communities in H₂-based MBfR to the impact of the gases’ back-diffusion. In this research, the denitrification performance and microbial dynamics were studied in a H₂-based MBfR operated at close-end mode with a fixed H₂ pressure of 0.04 MPa and fed with nitrate (NO₃⁻) containing influent. Results of single-factor and microsensor measurement experiments indicate that the H₂ availability was the decisive factor that limits NO₃⁻ removal at the influent NO₃⁻ concentration of 30 mg N/L. High-throughput sequencing results revealed that (1) the increase of NO₃⁻ loading from 10 to 20–30 mg N/L resulted in the shift of dominant functional bacteria from Dechloromonas to Hydrogenophaga in the biofilm; (2) excessive NO₃⁻ loading led to the declined relative abundance of Hydrogenophaga and basic metabolic pathways as well as counts of most denitrifying enzyme genes; and (3) in most cases, the decreased quantity of N metabolism-related functional bacteria and genes with increasing distance from the H₂ supply end corroborates that the microbial community structure in H₂-based MBfR was significantly impacted by the gases’ back-diffusion. Full article

In this study, we proposed an innovative oxidation–absorption method for low-temperature denitrification (160–240 °C), in which NO is initially catalytically oxidized by hydrogen peroxide (H₂O₂) vapor over titania-based catalysts, and the oxidation products are then absorbed by NaOH solution. The effects of flue gas temperature, molar H₂O₂/NO ratio, gas hourly space velocity (GHSV), and Fe substitution amounts of Fe/TiO₂ catalysts on the denitrification efficiency were investigated by a well-designed experiment. The results indicated that the Fe/TiO₂ catalyst exhibited a combination of remarkable activity and deep oxidation ability (NO converted into harmless NO₃⁻). In order to comprehend the functional mechanism of the Fe dopant’s local environment in TiO₂ support, the promotional effect of the calcination temperature of Fe/TiO₂ on the denitration performance was also studied. A tentative synergetic mechanism could be interpreted from two aspects: (1) Fe³⁺ as a substitute of Ti⁴⁺, leading to the formation of enriched oxygen vacancies at the surface, could significantly improve the adsorption efficiency of •OH; (2) the isolated surface Fe ion holds a strong adsorption affinity for NO, such that the adsorbed NO could be easily oxidized by the pre-formed •OH. This process offers a promising alternative for current denitrification technology. Full article

Alloying Pd with Cu is important for catalytic reactions such as denitrification reaction and CO oxidation reaction, but understanding of the catalyst preparation and its correlation with the catalyst’s activity and selectivity remains elusive. Herein, we report the results of investigations of the preparation of PdCu alloy nanocatalysts using different methods and the catalytic properties of the catalysts in catalytic denitrification reaction and CO oxidation reaction. PdCu alloy nanocatalysts were prepared by conventional dry impregnation method and ligand-capping based wet chemical synthesis method, and subsequent thermochemical activation as well. The alloying characteristics depend on the bimetallic composition. PdCu/Al₂O₃ with a Pd/Cu ratio of 50:50 was shown to exhibit an optimized hydrogenation activity for the catalytic denitrification reaction. The catalytic activity of the PdCu catalysts was shown to be highly dependent on the support, as evidenced by the observation of an enhanced catalytic activity for CO oxidation reaction using TiO₂ and CeO₂ supports with high oxygen storage capacity. Implications of the results to the refinement of the preparation of the alloy nanocatalysts are also discussed. Full article