Oxygen-limited Environment Research Articles

Comammox rather than AOB dominated the efficient autotrophic nitrification-denitrification process in an extremely oxygen-limited environment

The discovery of complete ammonia oxidizer (comammox) has challenged the traditional understanding of the two-step nitrification process. However, their functions in the oxygen-limited autotrophic nitrification-denitrification (OLAND) process remain unclear. In this study, OLAND was achieved using comammox-dominated nitrifying bacteria in an extremely oxygen-limited environment with a dissolved oxygen concentrations of 0.05 mg/L. The ammonia removal efficiency exceeded 97 %, and the total nitrogen removal efficiency reached 71 % when sodium bicarbonate was used as the carbon source. The pseudo-first- and second-order models were found to best fit the ammonia removal processes under low and high loads, respectively, suggesting distinct ammonia removal pathways. Full-length 16S rRNA gene sequencing and metagenomic results revealed that comammox-dominated under different oxygen levels, in conjunction with anammox and heterotrophic denitrifiers. The abundance of enzymes involved in energy metabolism indicates the coexistence of anammox and autotrophic nitrification-heterotrophic denitrification pathways. The binning results showed that comammox bacteria engaged in horizontal gene transfer with nitrifiers, anammox bacteria, and denitrifiers to adapt to an obligate environments. Therefore, this study demonstrated that comammox, anammox, and heterotrophic denitrifiers play important roles in the OLAND process and provide a reference for further reducing aeration energy in the autotrophic nitrogen removal process.

Insights into the evolutionary and ecological adaption strategies of nirS- and nirK-type denitrifying communities.

Denitrification is a crucial process in the global nitrogen cycle, in which two functionally equivalent genes, nirS and nirK, catalyse the critical reaction and are usually used as marker genes. The nirK gene can function independently, whereas nirS requires additional genes to encode nitrite reductase and is more sensitive to environmental factors than nirK. However, the ecological differentiation mechanisms of those denitrifying microbial communities and their adaptation strategies to environmental stresses remain unclear. Here, we conducted metagenomic analysis for sediments and bioreactor samples from Lake Donghu, China. We found that nirS-type denitrifying communities had a significantly lower horizontal gene transfer frequency than that of nirK-type denitrifying communities, and nirS gene phylogeny was more congruent with taxonomy than that of nirK gene. Metabolic reconstruction of metagenome-assembled genomes further revealed that nirS-type denitrifying communities have robust metabolic systems for energy conservation, enabling them to survive under environmental stresses. Nevertheless, nirK-type denitrifying communities seemed to adapt to oxygen-limited environments with the ability to utilize various carbon and nitrogen compounds. Thus, this study provides novel insights into the ecological differentiation mechanism of nirS and nirK-type denitrifying communities, as well as the regulation of the global nitrogen cycle and greenhouse gas emissions.

Low-oxygen-induced root bending is altered by phytoglobin1 through mediation of ethylene response factors (ERFs) and auxin signaling.

phytoglobin1 positively regulates root bending in hypoxic Arabidopsis roots through regulation of ethylene response factors and auxin transport. Hypoxia-induced root bending is known to be mediated by the redundant activity of the group VII ethylene response factors (ERFVII) RAP2.12 and HRE2, causing changes in polar auxin transport (PAT). Here, we show that phytoglobin1 (Pgb1), implicated in hypoxic adaptation through scavenging of nitric oxide (NO), can alter root direction under low oxygen. Hypoxia-induced bending is exaggerated in roots over-expressing Pgb1 and attenuated in those where the gene is suppressed. These effects were attributed to Pgb1 repressing both RAP2.12 and HRE2. Expression, immunological and genetic data place Pgb1 upstream of RAP2.12 and HRE2 in the regulation of root bending in oxygen-limiting environments. The attenuation of slanting in Pgb1-suppressing roots was associated with depletion of auxin activity at the root tip because of depression in PAT, while exaggeration of root bending in Pgb1-over-expressing roots with the retention of auxin activity. Changes in PIN2 distribution patterns, suggestive of redirection of auxin movement during hypoxia, might contribute to the differential root bending responses of the transgenic lines. In the end, Pgb1, by regulating NO levels, controls the expression of 2 ERFVIIs which, in a cascade, modulate PAT and, therefore, root bending.

Metagenomic 16S rRNA analysis and predictive functional profiling revealed intrinsic organohalides respiration and bioremediation potential in mangrove sediment

BackgroundMangrove sediment microbes are increasingly attracting scientific attention due to their demonstrated capacity for diverse bioremediation activities, encompassing a wide range of environmental contaminants.Materials and methodsThe microbial communities of five Avicennia marina mangrove sediment samples collected from Al Rayyis White Head, Red Sea (KSA), were characterized using Illumina amplicon sequencing of the 16S rRNA genes.ResultsOur study investigated the microbial composition and potential for organohalide bioremediation in five mangrove sediments from the Red Sea. While Proteobacteria dominated four microbiomes, Bacteroidetes dominated the fifth. Given the environmental concerns surrounding organohalides, their bioremediation is crucial. Encouragingly, we identified phylogenetically diverse organohalide-respiring bacteria (OHRB) across all samples, including Dehalogenimonas, Dehalococcoides, Anaeromyxobacter, Desulfuromonas, Geobacter, Desulfomonile, Desulfovibrio, Shewanella and Desulfitobacterium. These bacteria are known for their ability to dechlorinate organohalides through reductive dehalogenation. PICRUSt analysis further supported this potential, predicting the presence of functional biomarkers for organohalide respiration (OHR), including reductive dehalogenases targeting tetrachloroethene (PCE) and 3-chloro-4-hydroxyphenylacetate in most sediments. Enrichment cultures studies confirmed this prediction, demonstrating PCE dechlorination by the resident microbial community. PICRUSt also revealed a dominance of anaerobic metabolic processes, suggesting the microbiome’s adaptation to the oxygen-limited environment of the sediments.ConclusionThis study provided insights into the bacterial community composition of five mangrove sediments from the Red Sea. Notably, diverse OHRB were detected across all samples, which possess the metabolic potential for organohalide bioremediation through reductive dehalogenation pathways. Furthermore, PICRUSt analysis predicted the presence of functional biomarkers for OHR in most sediments, suggesting potential intrinsic OHR activity by the enclosed microbial community.

A Study on Physicochemical, Microbiological and Biochemical Properties of Wetland Soils in Eket, Akwa Ibom State, Nigeria

The physicochemical, microbiological and biochemical characteristics of wetland soils in the Eket Local Government Area were studied between March 2019 to February 2021. Soil samples were collected at depths of 0-15cm and 15-30cm and analyzed for physicochemical, Microbiological and Biochemical properties. Laboratory data obtained were subjected to statistical analysis. The results showed that sand particles dominated the particle size distribution, of the entire wetland soils, while silt and clay were very low. Chemical analysis revealed that the mean pH obtained was 6.2 ± 0.2, 6.45 ± 0.07, and 6.60 ± 0.14 for Ntak Inyang, Etebi, and Ekpene Obo wetland soils respectively. Similarly, the highest organic matter was obtained in Ekpene Obo (6.96 ± 0.74%) followed by Ntak Inyang (6.58 ± 2.69%), while Etebi had the least (4.89 ± 1.77%). The highest total nitrogen was obtained in Ekpene Obo (0.17 ± 0.02%), followed by Ntak Inyang (0.16 ± 0.07%) and Etebi having the least with (0.12 ± 0.04%). Ntak Inyang wetland soils had the highest biomass carbon (1.58 ± 00 µg-1) followed by Etebi (1.37 ± 0.44 µg-1), and Ekpene Obo the least (1.01 ± 00 µg-1). The highest biomass of Nitrogen was obtained in soils of Ekpene Obo (0.4 ± 0.01 µg-1) followed by Ntak Inyang (0.02 ± 0.02 µg-1) while soils of Etebi had the least (0.03 ± 0.01 µg-1). The Pearson correlation matrix showed that moisture content had a strong and negative relationship with bulk density (r = -0.69), while base saturation correlates positively with total nitrogen (r=0.681). Urease had a strong, and positive relationship with catalase (r=0.734), whereas bacteria relate negatively with total N (r=-0.801), and B.S (r=-0.781), but positively with catalase (r=-0.698). The negative correlation observed in most of the soil properties is a result of the low decomposition of organic matter in wetland soils, because anaerobic bacteria operate at a much slower energy level than aerobic bacteria, decomposition proceeds much more slowly in anaerobic and oxygen-limited environments such as wetlands.

Enhancing Photosynthesis Efficiency of Hydrogen Peroxide by Modulating Side Chains to Facilitate Water Oxidation at Low-Energy Barrier Sites.

Hydrogen peroxide (H2O2) is a crucial oxidant in advanced oxidation processes. In situ, photosynthesis of it in natural water holds the promise of practical application for water remediation. However, current photosynthesis of H2O2 systems primarily relies on oxygen reduction, leading to limited performance in natural water with low dissolved oxygen or anaerobic conditions found in polluted water. Herein, a novel photocatalyst based on conjugated polymers with alternating electron donor-acceptor structures and electron-withdrawing side chains on electron donors is introduced. Specifically, carbazole functions as the electron donor, triazine serves as the electron acceptor, and cyano acts as the electron-withdrawing side chain. Notably, the photocatalyst exhibits a remarkable solar-to-chemical conversion of 0.64%, the highest reported in natural water. Furthermore, even in anaerobic conditions, it achieves an impressive H2O2 photosynthetic efficiency of 1365µmolg-1h-1, surpassing all the reported photosynthetic systems of H2O2. This remarkable improvement is attributed to the effective relocation of the water oxidation active site from a high-energy carbazole to a low-energy acetylene site mediated by the side chains, resulting in enhanced O2 or H2O2 generation from water. This breakthrough offers a new avenue for efficient water remediation using advanced oxidation technologies in oxygen-limited environments, holding significant implications for environmental restoration.

Characterization of modern and waterlogged archaeological cypress (Glyptostrobus pensilis) wood: An analytical pyrolysis (Py-GC-MS and THM-GC-MS) and infrared spectroscopy (FTIR-ATR) study of within tree (radial) and decay-induced compositional variations

A fundamental understanding of the composition of archaeological wood stored under oxygen-limited environments, such as waterlogged sediments, is needed to inform preservation conditions of remains and to evaluate the validity of sediment and tree core-derived proxies of past environmental conditions. For this purpose, we determined chemical changes along the radial direction of archaeological (∼2000 yrs old) and modern (growth period 1948 to 2018 CE) wood of the Chinese swamp cypress (Glyptostrobus pensilis), an ethnobotanically important species in subtropical China, using conventional analytical pyrolysis (pyrolysis-gas chromatography-mass spectrometry; Py-GC-MS), pyrolysis with in situ methylation (thermally assisted hydrolysis and methylation; THM-GC-MS), and Fourier-transform infrared (FTIR) spectroscopy. The results showed 1) excellent preservation of the archaeological wood expressed by significant contributions of levoglucosan to the polysaccharides fingerprint after Py-GC-MS; 2) considerable chemical differences between archaeological and modern wood, i.e. archaeological wood samples yield relatively small proportions of lignin and large proportions of polysaccharides and terpenoids; 3) major differences in chemical characteristics of sapwood (more polysaccharides) and heartwood (more lignin). Furthermore, some tested decay proxies show large differences between sap- and heartwood (and are therefore of little value), yet the 4-acetylguaiacol/total guaiacol ratio (4AG/G; Py-GC-MS) of heart- and sapwood are similar, implying that this ratio is a more suitable proxy for decay assessment. Data comparison allowed to identify discrepancies and complementarities of Py-GC-MS, THM-GC-MS and FTIR for the characterization of different wood constituents and their preservation during long-term storage under waterlogged conditions. These results expand our understanding of the chemical composition of decomposing trunks of archaeological wood in general, and of G. pensilis in particular.

Investigation of Optical and Structural Properties of VO2 Thin Films by Thermal Treatment

In this study, VO2 thin films were grown on SiO2 substrate using the PLD method. Then the grown VO2 thin films were subjected to heat treatments at different temperatures and times in the atmosphere environment. The structural properties of the heat-treated films were investigated using X-ray diffraction (XRD) technique and Raman spectroscopy techniques. The surface microstructures of these films were investigated by Scanning Electron Microscope (SEM) technique, and their optical properties and bond structures were investigated by Photoluminescence (PL) spectra and Fourier Transform Infrared Spectroscopy (FTIR) measurements, respectively. Especially XRD and Raman results revealed that heat treatments with high temperature values transformed the films into VO2 and V2O5 mixed-phase crystal structures. Due to the heat treatment carried out in the atmosphere and the high oxygen affinity of the vanadium metal, crystallization took place in both VO2 and V2O5 forms. In order to obtain homogeneous crystalline VO2 structures, heat treatments should be carried out for a long time in oxygen-limited environments.

Screening of potential donors for anaerobic stress tolerance during germination in rice.

The rising cost of transplanting rice has made direct seeding an affordable alternative for rice establishment, particularly in Africa. However, direct seeding, while cost-effective, faces crop establishment challenges due to flooding. Uncontrolled water, driven by erratic rains in low-lying areas or uneven fields, limit germination. Rice possesses the unique ability of anaerobic germination, enabling it to sprout and emerge in oxygen-deprived conditions. Understanding rice's response to anaerobic stress during germination is crucial for resilience breeding. Africa, although relying on direct seeding, has made limited progress in addressing flooding during germination compared to Asia. Anaerobic stress tolerance ensures successful crop emergence even in oxygen-limited environments and can help suppress weeds, a significant challenge in direct-seeded rice cultivation. This study aims to contribute by screening for potential rice donors exhibiting anaerobic stress tolerance. We screened 200 rice genotypes at Sokoine University of Agriculture (SUA) in Morogoro, Tanzania, primarily focusing on landraces with untapped potential. Using an alpha lattice design, we conducted two anaerobic experiments in September and October 2022, adding 7cm of standing water immediately after dry seeding for flooded and maintaining a 2cm water level after germination in the control for duration of 21 days. We identified potential donors based on selection index computed from genomic estimated breeding values (GEBVs) using eight variables: germination at 14 DAS, germination at 21 DAS, seedling height at 14 DAS, seedling height at 21 DAS, shoot dry matter at 21 DAS, root dry matter at 21 DAS, culm diameter at 21 DAS, and root length at 21DAS. Ten genotypes emerged as the most promising, exhibiting at least 70% germination in floodwater at 21 DAS and greater selection indices. These genotypes were like: Afaa Mwanza 1/159, Rojomena 271/10, Kubwa Jinga, Wahiwahi, Magongo ya Wayungu, Mpaka wa Bibi, Mwangaza, Tarabinzona, IB126-Bug 2013A, and Kanamalia with respective percentages of 75, 74, 71, 86, 75, 80, 71, 80, 70, and 73. These findings contribute to global efforts to mitigate the impacts of flooding during germination. These donors, will be potential to enrich the gene pool for anaerobic germination, providing valuable resources for breeding for flooding tolerance.

To explore the remediation mechanism and effect of biochar and KH2PO4 on soils contaminated with heavy metal ions Hg2+, Cd2+ and Pb2+

In this study, wheat straw-derived biochar was prepared by setting a temperature of 400 °C under an oxygen-limited environment using the technique of “programmed temperature increase control”. The results showed that the biochar had a strong adsorption capacity for Hg2+, Cd2+ and Pb2+ ions, and the adsorption pattern was Hg2+>Cd2+>Pb2+. There was a competitive adsorption effect during the coexistence of the ions. The results of the soil remediation tests showed that the effects of biochar on soil physicochemical properties and heavy metal distribution was generally greater than those of KH2PO4 in single or combined contaminated soil. The adsorption effect of heavy metal ions in soil was the best in the case of mixed additions. The results can provide a scientific basis for the treatment of heavy metal contaminated soil with wheat straw biochar in the future.

Kinetics, stoichiometry, and mechanism of arsenopyrite-water interaction under anoxic conditions

Arsenopyrite dissolution is an important source of arsenic’s environmental occurrence and is well-studied under oxidative conditions. However, little is known of anoxic leaching of arsenopyrite by water, though it is probably one of the dominant abiotic processes controlling arsenic mobility in oxygen-limited environments such as groundwaters and paddy fields. The present study attempts to probe the mechanism of arsenopyrite-water interaction in anoxic environment through examining the pH dependence of dissolution kinetics and stoichiometry, as well as speciation changes both on the surface and in solution. Batch and flow-through experiments were first carried out to measure dissolution rates and the results showed alkaline pH mildly encourages As release. Furthermore, the dissolution was found to be near stoichiometric with respect to As and S but not with Fe/As or Fe/S, and the non-stoichiometry exhibited a negative dependence on pH. Combining speciation analyses that revealed the presence of H2O2, SO42− and S2O32− in solutions and a positive correlation of surface species Fe(III)-O, S(-II), and As(I), As(III), As(V), and As(-III) to solution pH, we interpreted the anoxic dissolution behavior of arsenopyrite through a mechanism that combines surface complexation and interfacial redox reactions. The kinetic measurements came to be concerning as data indicates arsenopyrite dissolution in anoxic environment can lead to water having arsenic concentrations above the 10 ppb WHO guideline value in one day at the experimental conditions. The observed H2O2 production indicated the dissolution is associated with or initiated by electron transfer despite the anoxic condition, further suggesting that a more comprehensive theory other than surface complexation model may be needed to better understand the geochemical behavior of As and possibly S in the context of sulfide mineral–water interactions.

Competitive and substrate limited environments drive metabolic heterogeneity for comammox Nitrospira

Nitrospira has been revealed as a high versatile genus. Although previously considered only responsible for the conversion of nitrite to nitrate, now we know that Nitrospira can perform complete ammonia oxidation to nitrate too (comammox). Comammox activity was firstly reported as dominant in extremely limited oxygen environments, where anaerobic ammonia oxidation was also occurring (anammox). To explain the comammox selection, we developed an Individual-based Model able to describe Nitrospira and anammox growth in suspended flocs assembled in a dynamic nitrogen and oxygen-limiting environment. All known and hypothesized nitrogen transformations of Nitrospira were considered: ammonia and nitrite oxidation, comammox, nitrate-reducing ammonia oxidation, and anaerobic nitrite-reducing ammonia oxidation. Through bioenergetics analysis, the growth yield associated to each activity was estimated. The other kinetic parameters necessary to describe growth were calibrated according to the reported literature values. Our modeling results suggest that even extremely low oxygen concentrations (~1.0 µM) allow for a proportional growth of anammox versus Nitrospira similar to the one experimentally observed. The strong oxygen limitation was followed by a limitation of ammonia and nitrite, because anammox, without strong competitors, were able to grow faster than Nitrospira depleting the environment in nitrogen. These substrate limitations created an extremely competitive environment that proved to be decisive in the community assembly of Nitrospira and anammox. Additionally, a diversity of metabolic activities for Nitrospira was observed in all tested conditions, which in turn, explained the transient nitrite accumulation observed in aerobic environments with higher ammonia availability.

Carbon Sequestration Strategies in Soil Using Biochar: Advances, Challenges, and Opportunities.

Biochar, a carbon (C)-rich material obtained from the thermochemical conversion of biomass under oxygen-limited environments, has been proposed as one of the most promising materials for C sequestration and climate mitigation in soil. The C sequestration contribution of biochar hinges not only on its fused aromatic structure but also on its abiotic and biotic reactions with soil components across its entire life cycle in the environment. For instance, minerals and microorganisms can deeply participate in the mineralization or complexation of the labile (soluble and easily decomposable) and even recalcitrant fractions of biochar, thereby profoundly affecting C cycling and sequestration in soil. Here we identify five key issues closely related to the application of biochar for C sequestration in soil and review its outstanding advances. Specifically, the terms use of biochar, pyrochar, and hydrochar, the stability of biochar in soil, the effect of biochar on the flux and speciation changes of C in soil, the emission of nitrogen-containing greenhouse gases induced by biochar production and soil application, and the application barriers of biochar in soil are expounded. By elaborating on these critical issues, we discuss the challenges and knowledge gaps that hinder our understanding and application of biochar for C sequestration in soil and provide outlooks for future research directions. We suggest that combining the mechanistic understanding of biochar-to-soil interactions and long-term field studies, while considering the influence of multiple factors and processes, is essential to bridge these knowledge gaps. Further, the standards for biochar production and soil application should be widely implemented, and the threshold values of biochar application in soil should be urgently developed. Also needed are comprehensive and prospective life cycle assessments that are not restricted to soil C sequestration and account for the contributions of contamination remediation, soil quality improvement, and vegetation C sequestration to accurately reflect the total benefits of biochar on C sequestration in soil.

Development of a novel biochar-made porous monolith for enhanced C1 and H2 fermentation

Biochar is a carbonaceous porous material that is produced through the thermal processing of biomass under oxygen-limited environment. Nevertheless, biochar is known to be an inexpensive and sustainable raw material with a wide range of possible applications. Recently, biochar has been discovered as an efficient biological catalyst for anaerobic conversion, mainly due to its highly porous structure with micro and macro channels, which procures a viable living area for attached-grown microorganisms. Whereas it is never applied to improve the biological conversion of gas substances such as C1 (e.g., CO, CO2) and H2, which is a promising research area with increasing commercial interest. However, considering that biological reaction is limited by the target water solubility of gas substrates, special attention is required when combining biochar for gas fermentation. The goal was to create a novel gas sparger where the biofilm grows on biochar, thus improving the interaction with the gaseous substrate. For this purpose, polystyrene foam and powdered biochar were compounded to form a mouldable composite, which was then cast as a porous monolith.•Biochar-made sparger (BS) was investigated for the homoacetogenic conversion of H2 gas via microbial mixed cultures as opposed to a control test equipped with a stone sparger.•BS showed a significantly better performance in terms of biological gas fixation rate (36% more than control) and productivity (8.5 gCOD L−1 d−1).

Enhancement of Methylene Blue Adsorption from ZnO/Activated Carbon Nanocompossites Prepared by Pyrolysis of Molten ZnCl2 with Rice Husks

In this work, we synthesized a facile step pyrolysis of ZnO/activated carbon nanocomposites by using molten ZnCl2 and rice husks in oxygen-limited environment. The mass ratio of molten ZnCl2 and rice husks was chosen from 0 to 5 wt.%, the pyrolysis temperature range from 400 to 800 oC. When the mass ratio of molten ZnCl2 and rice husks was equal to 1.0 and the pyrolysis temperature was at 800 oC, the size of ZnO nanoparticles in diameter was found to be of 10-20 nm. The ZnO/activated carbon nanocomposites exhibited a porous structure with the BET surface area, average pore diameter and pore volume of 643.9 m2/g, 4,76 nm and 0.255 cm3/g, respectively. To investigate the adsorption behavior of methylene blue, batch experiments were performed on all samples. The ZnO/activated carbon sample manufactured at a mass ratio of 1.0 and a pyrolysis temperature of 800 oC has the best methylene blue adsorption capability. The Langmuir isotherm was used to calculate the maximum adsorption capacity of methylene blue, which was 814.9 mg/g. Based on the obtained results, one can suggest that ZnO/activated carbon nanocomposites prepared by the facile pyrolysis route from molten ZnCl2 and rice husks possessing eco-friendly behaviour and low productioncost can be used as a potential adsorbent for wastewater treatment.

Ammoniacal and Nitrate Nitrogen Release Pattern from Biochar and Biochar Blended Urea Fertilizers in Sandy Soil

Biochar, an organic product of thermal decomposition of biomass in an oxygen limited environment can be used as a nutrient carrier to delay the release of nutrients into the soil, reduce nutrient leaching, and improve the nutrient utilization efficiency of fertilizers. Nutritional enhancement of biochar through fertilizer blending could be a low cost but high efficiency solution compared to non-blended fertilizers. However, the rate of nutrient release from the blended biochar fertilizer in different soils is ambiguous. Hence a 12 month incubation study was conducted in sandy soil (ultisol) of Thiruvananthapuram district of Kerala to elucidate the ammoniacal and nitrate nitrogen release rate and pattern from the produced paddy husk biochar, biochar and biochar bentonite (1:1) each blended with urea fertilizer in different ratios (1:0.5, 1:1, 1:2) including an absolute control. The individual effects of biochar, biochar-bentonite and urea were also studied. Paddy husk biochar was produced by the process of slow pyrolysis and biochar- blended urea fertilizers by the adsorbent process. To evaluate the influence of bentonite clay on the nutrient release pattern of biochar, it was blended with biochar and urea fertilizer. The highest total nitrogen content among the produced fertilizers was recorded in biochar: urea in 1:2 (33.04%) followed by biochar-bentonite: urea in a 1:2 ratio (31.13%). The incubation study revealed that the maximum release of ammoniacal nitrogen from soil+ urea fertilizer was at 30 days (115.73 mg kg-1) followed by a sharp decline, maintaining a low value till the end of incubation, whereas the release was sustained and gradually increased to reach a maximum at the 180th day (117.6 mg kg-1) for soil+ biochar: urea in 1:1 ratio. Nitrate nitrogen also followed the same trend with the maximum release observed for biochar: urea in 1:1 on the 150th day (151.2 mg kg-1). The release of nitrate nitrogen was more than that of ammoniacal nitrogen throughout the incubation period for all the treatments. Among the blended fertilizers, content of both ammoniacal and nitrate nitrogen were comparatively less for biochar –bentonite blended urea fertilizers. Thus, blending of urea with biochar/ biochar-bentonite prolonged the duration of maximum nutrient release.

Optimization of fermentation conditions as a metabolic strategy for the high-yield and high-selectivity bio-based 2,3-butanediol production

Optimization of culture conditions can be used as an alternative metabolic control strategy to genetic engineering to improve bio-based 2,3-butanediol (2,3-BDO) production, especially its yield and optical purity. In this study, a first-order model was determined to predict the 2,3-BDO yield, which reached about 90% in batch cultures at 32° C, pH = 5, and kLa ∼ 5.0 ± 2.7 h−1, using a new and safe Paenibacillus peoriae NRRL BD-62. No acetoin accumulation and an absolute levo-2,3-BDO optical purity were also verified. About 39.4 g/L of 2,3-BDO, with a yield of 0.43 g/g, and a levo-:meso-2,3-BDO ratio of 1.9:1, was obtained at the expense of acetoin, lactic acid, and ethanol in fed-batch fermentation at kLa adjusted within its optimized range (∼7.5 h−1) to overcome operational limitations using high initial glucose concentrations. The low pH contributed to the carbon flux shift toward the levo-isomer synthesis, possibly due to the preferential butanediol dehydrogenase activation, while the highly oxygen-limited environment favored the complete acetoin conversion, enhancing the 2,3-BDO yield. These results provide significant contributions to the high-yield, acetoin-free, and safe bio-based 2,3-BDO production of particular interest in large-scale fermentations.

The Growth and Evolution of Biomass Soot in Partial Oxidation-Assisted Hot Gas Filtration

At present, partial oxidation is applied in the filtration processes of biomass hot gas to aid in solving the blockage problems caused by tar and dust condensates. However, in the resulting high-temperature and oxygen-limited environment, the risk of tar polymerization forming soot is created during the purification processes. Thus, this work established a hardware-in-the-loop simulation model using the Lagrangian method coupled with the chemical reactions on the particle surface. The model was then used to simulate the entire evolution process of soot, including its formation, growth, and interception. The simulation results confirmed that under partial oxidation conditions, the increase in tar’s conversion rate promotes the formation of soot. Further analysis indicated that the high-temperature field formed as a result of oxidation and the increase in the naphthalene/oxygen ratio are the main reasons for the soot formation. On the other hand, the growth process of soot was inhibited by partial oxidation, which is mainly reflected in the relatively smaller increasing magnitude of soot particle mass and the decrease in the soot formation rate. Although the formation and growth of biomass soot cannot be completely avoided, the growth process is beneficial to interception and the soot escape rate can be minimized by varying the premixed oxygen content. On this basis, the potential of the partial oxidation-assisted hot gas filtration method can be further investigated and analyzed.

Partial Nitrification Characteristics of an Immobilized Carrier in Municipal Wastewater under Low-Temperature Shock: The Role of the Nitrifying Bacterial Community Structure

To analyze the effects of the nitrifying bacterial community structure on the partial nitrification (PN) characteristics in a PN-immobilized carrier in municipal wastewater under low-temperature shock, two PN-immobilized carriers with different nitrifying bacterial communities were investigated. The E1-immobilized carrier contained a high abundance of ammonia-oxidizing bacteria (AOB; 38.59%), and the E2-immobilized carrier had a low AOB abundance of 4.78%. The results of experiments with different dissolved oxygen (DO) concentrations showed that the oxygen-limited environment inside the immobilized carrier, generated by the high AOB abundance, was critical for achieving PN. The nitrite accumulation rate (NAR) decreased from 90.0–93.9% to 84.2–88.3% for the E1-immobilized carrier and from 86.0–90.4% to 81.7–85.8% for the E2-immobilized carrier under low-temperature shock (the temperature suddenly decreased from 25 ± 1 °C to 15 ± 1 °C). The decrease in the ammonia oxidation rate due to the decreased AOB activity led to a decrease in NAR. Moreover, NOB abundance in the E2-immobilized carrier increased because of the destruction of the oxygen-limiting region in the immobilized carrier due to the low AOB abundance. Increasing the abundance of AOB in the PN-immobilized carrier could reduce the adverse effects from the low-temperature shock. The results of this study can be used to further develop immobilization technology for efficient PN in mainstream wastewater treatment.

Performance of rotating cage biological contactors based on the partial nitrification of immobilized bioactive fillers

The rotating cage biological contactors (RCBC) is based on the partial nitrification immobilization of bioactive fillers, incorporating the advantages of traditional the rotating biological contactor (RBC). The RCBC is more energy-efficient, with higher ammonia oxidation rate (AOR) and nitrite accumulation rate (NAR) levels compared to the RBC Under the conditions of different rotational speeds and immersion rates of an RCBC, the volumetric oxygen transfer coefficient (KLa) was measured. The experimental results show that these two factors significantly affected the KLa of the reactor, which ranged from 1.08 to 42.02 h−1. Regarding long-term ammonia oxidation performance, the RCBC can successfully start partial nitrification in only 5 days. After stable operation, the AOR was 23.34 ± 0.55 mg (L·h)−1, with an NAR of 93.42 ± 0.84 %. This indicates a good adaptability to variations in influent ammonia nitrogen (NH4+-N) in the range of 95.92–403.14 mg·L−1 and good resistance to free nitrous acids (FNA). In addition, high-throughput sequencing analysis showed that the operation mode of the RCBC could effectively inhibit the growth of nitrite-oxidizing bacteria (NOB) in immobilized bioactive fillers, and the internal oxygen-limited environment provided favorable conditions for reducing the relative abundance and activity of NOB. In this study, a partial nitrification device was established by immobilized bioactive fillers in the form of an RCBC for the first time, providing a partial nitrification technology without aeration.