Inhibition of urease activity by humic acid extracted from sludge fermentation liquid

Effect of sludge humic acid-derived nano-biochars on anaerobic degradation of sulfamethoxazole by Shewanella oneidensis MR-1

Some nano-biochars (nano-BCs) as electron mediators could enter into cells to directly promote intracellular electron transfer and cell activities. However, little information was available on the effect of nano-BCs on SMX degradation. In this study, nano-BCs were prepared using sludge-derived humic acid (SHA) and their effects on SMX degradation by Shewanella oneidensis MR-1 were investigated. Results showed that nano-BCs (Carbon dots, CDs, <10 nm) synthesized using SHA performed a better accelerating effect than that of the nano-BCs with a larger size (10-100 nm), which could be attributed to the better electron transfer abilities of CDs. The degradation rate of 10 mg/L SMX in the presence of 100 mg/L CDs was significantly increased by 84.6% compared to that without CDs. Further analysis showed that CDs could not only be combined with extracellular Fe(III) to accelerate its reduction, but also participate in the reduction of 4-aminobenzenesulphonic acid as an intermediate metabolite of SMX via coupling with extracellular Fe(III) reduction. Meanwhile, CDs could enter cells to directly participate in intracellular electron transfer, resulting in 32.2% and 25.2% increases of electron transfer system activity and ATP level, respectively. Moreover, the activities of SMX-degrading enzymes located in periplasm and cytoplasm were increased by around 2.2-fold in the presence of CDs. These results provide an insight into the accelerating effect of nano-BCs with the size of <10 nm on SMX degradation and an approach for SHA utilization.

Synthesis of artificial humic acid-urea complex improves nitrogen utilization

The inefficient use of conventional nitrogen (N) fertilizers leads to N enrichment in the soil, resulting in N loss via runoff, volatilization and leaching. While using artificial humic acid to prepare novel N fertilizer is a good choice to improve its efficiency, the high heterogeneity of artificial humic acid limits its structural analysis and utilization efficiency. To solve above problems, this work mainly carried out the fractionation experiments, melt penetration experiments and soil incubation experiments. The results revealed that four fractions with different aromatization degree and molecular weights were obtained by the newly proposed continuous dissolution method, particular in the extraction solution of pH = 3-4, which were extracted with the highest aromatization degree. Furthermore, artificial humic acid urea complex fertilizers prepared at pH = 3-4 significantly improved the release of NH4+-N by 38.32% on days 7 and NO3--N by 10.30% on days 14, compared to urea application. The highly aromatic complex fertilizer with loading of urea-N was able to supply more inorganic N to the soil on days 3-14 (low molecular weight N) and to maintain a higher N content on days 70 (highly aromatized N). This can partially offset the mineralization of readily available organic N, buffering the immobilization of inorganic N from the soil when unstable organic compounds (e.g. conventional urea) were incorporated. A-HAU3-4 addition on days 70, Proteobacteria and Actinobacteriota were found to be the dominant phylum in the soil and the relative abundance of Endophytic bacteria was increased, which was conducive to the improvement of soil N utilization efficiency and soil N sequestration. Therefore, the preparation of artificial humic urea fertilizer with high aromatization degree or low molecular weight were an effective way to improve N utilization efficiency in the initial stages of soil incubation and maintain N fixation in the later stages of soil incubation. The future application of the strategy presented by this study would have an important ecological significance for alleviating agricultural N pollution.

Transcriptomic analysis of humic acid in relieving the inhibitory effect of high nitrogen on soybean nodulation

Introduction

Nitrogen fertilizer intake promotes soybean growth before the formation of nodules, but excess nitrogen has an inhibitory effect on soybean nodulation. It is important to balance nitrogen levels to meet both growth and nodulation needs.

Methods

the nitrogen level suitable for soybean growth and nodulation was studied, the role of humic acid (HA) in alleviating the inhibition of high nitrogen on soybean nodulation was analyzed, and transcriptomic analysis was performed to understand its mechanism.

Results

The results showed that a lower level of nitrogen with 36.4 mg urea per pot could increase the number of nodules of soybean, and a higher level of nitrogen with 145.9 mg urea per pot (U4 group) had the best growth indicators but inhibited nodulation significantly. HA relieved the inhibitory effect at high nitrogen level, and the number of nodules increased by 122.1% when 1.29 g HA was added (H2 group) compared with the U4 group. The transcriptome analysis was subsequently performed on the H2 and U4 groups, showing that there were 2995 differentially expressed genes (DEGs) on the 25th day, accounting for 6.678% of the total annotated genes (44,848) under the test conditions. These DEGs were enriched in mitogen-activated protein kinase signaling pathway-plant, flavonoid biosynthesis, and plant hormone signal transduction based on the -log10 (P adjusted) value in the Kyoto Encyclopedia of Genes and Genomes pathway (KEGG).

Discussion

HA balanced the nitrogen level through the above pathways in soybean planting to control the number of nodules.

Monitoring of biofilm development and physico-chemical changes of floating microplastics at the air-water interface

Microplastics in the aquatic environment serve as a habitat for microbial life, on which they can form biofilms. However, how the development of the biofilm alters the properties of floating microplastics that are at the air-water interface and, therefore, not fully submerged, is not well understood. In this context, an aging experiment was conducted to monitor biofilm formation and changes in physico-chemical properties of low-density polyethylene (floating) microplastics over time. The growth of the biofilm followed the typical bacterial/biofilm growth phases and reached about 30% of the total mass of the microplastics, while the concentration of extracellular polymeric substances within the biofilm remained stable. Presence of chlorophyll a and urease activity indicated presence of photosynthetic microrganisms within the biofilm which was also confirmed by analysis of the biofilm composition. Chemical characterization by FTIR showed the formation of additional functional groups attributed to the formed biofilm, and SEM imaging showed cracks on the surface of the aged microplastics, indicating incipient degradation of the polyethylene. Moreover, the adsorption capacity of the aged particles for metals (Pb(II)) was 52% higher compared to the pristine ones. Aging increased the density and size of the particles; however, it did not lead to the submersion of the aged particles even after 12 weeks of aging, suggesting that additional environmental processes may influence the transport of microplastics from the air-water interface into the water body.

Influence of humic acid on microbial induced carbonate precipitation for organic soil improvement

Microbial induced carbonate precipitation (MICP) is one of the most commonly researched topics on biocementation, which achieves cementation of soil particles by carbonate from urea hydrolysis catalyzed by microbial urease. Although most MICP studies are limited to stabilizing sandy soils, more researchers are now turning their interest to other weak soils, particularly organic soils. To stabilize organic soils, the influence of humic substances should be investigated since it has been reported to inhibit urease activity and disrupt the formation of calcium carbonate. This study investigates the effect of humic acid (HA), one fraction of humic substances, on MICP. For this purpose, the effects of HA content on CaCO₃ precipitation using three strains and on CaCO₃ morphology were examined. The results showed that native species in organic soils were less adversely affected by HA addition than the exogenous one. Another interesting finding is that bacteria seem to have strategies to cope with harsh conditions with HA. Observation of CaCO₃ morphology revealed that the crystallization process was hindered by HA to some extent, producing lots of fine amorphous precipitates and large aggregated CaCO₃. Overall, this study could provide an insightful understanding of possible obstacles when using MICP to stabilize organic soils.

Spectroscopic investigation of conformational changes in urease caused by interaction with humic acid

Urease in soil interacts with humic acid (HA), which results in a change of the enzymatic activity and stability. However, knowledge on the conformational change of urease in the presence of HA is still lacking. Therefore, the structure of urease (net zero charge at pH 5.2) interacting with HA and the microenvironments of the tyrosine (Tyr) and tryptophane (Trp) residues were investigated at pH 6.7 and 8.0 and 0.5 and 50 mmol L^-1 KCl using spectroscopic techniques. Fluorescence intensity of urease was progressively inhibited by HA with increasing mass ratio f of HA/urease. Moreover, quenching of urease fluorescence by HA was strongest at pH 6.7 (and 50 mmol L^-1 KCl) where the hydrophobic attraction was counteracted by only a weak electrostatic repulsion. HA exerted only a minor effect on the positions of the maximum excitation bands for Tyr and Trp residues, indicating insignificant changes in the microenvironment of these residues in the presence of HA. At pH 6.7, the amide I and amide II bands were inhibited by HA. Curve-fitting of the amide I band of urease in complexes indicated that the percentages of α-helix, β-sheet and β-turn were changed. At pH 8 HA had little effect on the circular dichroism and attenuated total reflectance Fourier transform infrared spectra of urease. At this pH the interaction between urease and HA was weak due to the relatively strong electrostatic repulsion and the conformational change was insignificant. The present results increase our understanding of negatively charged protein behavior in natural environments dominated by humic substances.

Humic acid complex formation with urea alters its structure and enhances biomass production in hydroponic maize

BACKGROUND

Humic acid (HA)-enhanced urea (HAU) is the top-selling efficiency-enhanced urea in China. Comprehensive investigation into the structure and efficacy of HA complex formation with urea (HACU) - the main reaction product during HAU's production - is required to clarify the reaction mechanism between HA and urea, and to provide guidance for the development of high-efficiency HAU.

RESULTS

HACU showed discrepant structural and compositional features from raw HA. Nitrogen (N) content in HACU was 7.3 times greater than that of HA. Several high-resolution analytical methods showed a sharp increase of ammonia in the gaseous product during HACU pyrolysis, suggesting that urea contributed N to HACU. HACU was characterized with significantly fewer carboxyl groups than in raw HA, implying that the carboxyl group was the main group in HA to participate in the reaction between HA and urea. The presence of amide-N in HACU verified the structure of the reaction product. Furthermore, both HACU and HA could enhance the biomass in hydroponically grown maize seedlings, but the highest stimulation for HACU came about when its carbon concentrations were 50-100 mg L^-1 , higher than the optimal carbon concentration for HA (25 mg L^-1 ), attributed to the lower carboxyl group content for HACU to some extent.

CONCLUSION

During HAU's production, reaction with N derived from urea to form amide-N decreased the carboxyl groups in HA, leading to higher concentrations for HACU required to achieve the similar bioefficacy of HA. © 2021 Society of Chemical Industry.

Is the climate change mitigation effect of enhanced silicate weathering governed by biological processes?

A number of negative emission technologies (NETs) have been proposed to actively remove CO₂ from the atmosphere, with enhanced silicate weathering (ESW) as a relatively new NET with considerable climate change mitigation potential. Models calibrated to ESW rates in lab experiments estimate the global potential for inorganic carbon sequestration by ESW at about 0.5-5 Gt CO₂  year^-1 , suggesting ESW could be an important component of the future NETs mix. In real soils, however, weathering rates may differ strongly from lab conditions. Research on natural weathering has shown that biota such as plants, microbes, and macro-invertebrates can strongly affect weathering rates, but biotic effects were excluded from most ESW lab assessments. Moreover, ESW may alter soil organic carbon sequestration and greenhouse gas emissions by influencing physicochemical and biological processes, which holds the potential to perpetuate even larger negative emissions. Here, we argue that it is likely that the climate change mitigation effect of ESW will be governed by biological processes, emphasizing the need to put these processes on the agenda of this emerging research field.

Integrated Instillation Technology for the Synthesis of a pH-Responsive Sodium Alginate/Biomass Charcoal Soil Conditioner for Controlled Release of Humic Acid and Soil Remediation

In this work, pH-responsive gel spheres for controlled release of humic acid (CSGCHs) were prepared by an integrated instillation technology using a composite material of sodium alginate (SA) and charcoal activated carbon (CAC) as a carrier, and their slow-release performance, pH-responsive performance, and soil amendment performance were investigated. The results showed that the prepared CSGCH was uniform in size with obvious base responsiveness. Soil remediation experiments revealed that CSGCH could play a good role in the remediation of different types of soils. After 50 days of remediation, the content of nutrients and organic matter in the soil increased significantly and the pH and salt content of saline soils decreased by 15.2 and 29.8%, respectively. The plant experiment showed that CSGCH could effectively promote the growth of crops. Therefore, the prepared soil conditioner has a great potential value for improving soil conditions and promoting crop growth in agricultural applications.

Soil urease inhibition by various plant extracts

Urea is the most popular and widely used nitrogenous fertilizer. High soil urease activity rapidly hydrolyses applied urea to ammonia which contributes to soil nitrogen (N) losses and reduces N use efficiency of crop plants. The ammonia losses can be minimized by the inhibition of soil urease activity which has been explored using various potential chemical inhibitors. However, the soil urease activity inhibition potential of plant extracts is rarely explored to date. In the present study, extracts of 35 plant materials were taken and evaluated against jack bean urease. Eleven extracts, showing >50% jack bean urease inhibition, were selected and further investigated in 13 soils collected from various districts of Punjab, Pakistan. Interestingly, except Capsicum annum, Melia azedarach, Citrus reticulata and Quercus infectoria, the plant extracts showed urease inhibition activities in soils, the extent of which was lower as compared to that observed in jack bean urease though. Maximum urea hydrolysis inhibition (70%) was noted with Vachellia nilotica which was 40% more than that of hydroquinone (50%) followed by that of Eucalyptus camaldulensis (24%). The extracts of V. nilotica and E. camaldulensis were coated on urea and applied to soil in the next step. At 21st day, 239% and 116% more urea-N was recovered from soil treated with V. nilotica and E. camaldulensis extracts coated urea, respectively, as compared to uncoated urea. Conclusively, these results indicated that the coating of V. nilotica and E. camaldulensis extracts on urea prills prolonged urea persistence in soil owing to minimum urea hydrolysis, probably, the extracts of V. nilotica and E. camaldulensis showed their urease inhibition potential. The results of this study provide a base line for the identification of new soil urease inhibitor compounds from plant materials in future.

Effect of Municipal Solid Waste Compost on Antimony Mobility, Phytotoxicity and Bioavailability in Polluted Soils

The effect of a municipal solid waste compost (MSWC), added at 1 and 2% rates, on the mobility, phytotoxicity, and bioavailability of antimony (Sb) was investigated in two soils (SA: acidic soil; SB: alkaline soil), spiked with two Sb concentrations (100 and 1000 mg kg−1). The impact of MSWC on microbial activity and biochemical functioning within the Sb-polluted soils was also considered. MSWC addition reduced water-soluble Sb and favored an increase in residual Sb (e.g., by 1.45- and 1.14-fold in SA-100 and SA-1000 treated with 2% MSWC, respectively). Significant increases in dehydrogenase activity were recorded in both the amended soils, as well as a clear positive effect of MSWC on the metabolic activity and catabolic diversity of respective microbial communities. MSWC alleviated Sb phytotoxicity in triticale plants and decreased Sb uptake by roots. However, increased Sb translocation from roots to shoots was recorded in the amended soils, according to the compost rate. Overall, the results obtained indicated that MSWC, particularly at a 2% rate, can be used for the recovery of Sb-polluted soils. It also emerged that using MSWC in combination with triticale plants can be an option for the remediation of Sb-polluted soils, by means of assisted phytoextraction.

Synthesis of nano-zirconium-iron oxide supported by activated carbon composite for the removal of Sb(v) in aqueous solution

In this study, nano zirconium iron oxide based on activated carbon (ZIC) was successfully prepared by using the coprecipitation method. Compared with unmodified activated carbon, ZIC increases the number of active sites by adding metal oxides and hydroxyl groups and greatly improves the adsorption capacity of Sb(v). The synthesized nanocomposites were characterized and analysed by XRD, SEM, FT-IR, VSM and other techniques. The results showed that the zirconium iron oxide particles were successfully loaded and uniformly distributed on the surface of the activated carbon, and the agglomeration phenomenon was reduced. The saturation magnetization of ZIC was 1.89 emu g⁻¹, which easily achieved solid–liquid separation under the action of an external magnetic field. In batch experiments, when the initial concentration was 1 mg L⁻¹, the dosage of ZIC was 600 mg L⁻¹, the pH value was 5.0, the contact time was 180 min, and the removal rate of Sb(v) reached 97.82%. The maximum adsorption capacity of ZIC for Sb(v) was 11.80 mg g⁻¹. Under the interference of various inorganic ions and dissolved organics, the excellent adsorption capacity was still due to ZIC. The adsorption form was multimolecular-layer adsorption, the adsorption process was an endothermic reaction, and chemical adsorption was dominant as the adsorption mechanism. ZIC has good removal efficiency and is reusable, which indicates that ZIC has prospects for practical wastewater treatment.

The adsorbent was highly effective in the removal of Sb(v). The adsorbent easily achieved solid–liquid separation under the action of an external magnetic field.

Stable isotopes reveal the formation diversity of humic substances derived from different cotton straw-based materials

Humic substances (HS) are essential in environment processes and carbon (C) sequestration in soils. In this study, organic materials such as cotton straw and its derived compost and biochar were added to the soil on a C-equivalent basis and incubated for 30 and 180 days in order to investigate the different forms of plant biomass derived C sequestration in HS. The C distribution in humic acid (HA), fulvic acid (FA), and humin (Hu) derived from organic materials was investigated using the ¹³C isotope method, while the catalase, sucrose, and β-glucosidase activities were also determined. The results showed that C3 distribution of Hu derived from straw, compost and biochar increased from 40.94% to 67.12%, 74.47% and 80.75%, respectively. In addition, the increase of C3 distribution of HA or FA derived from straw, compost and biochar were 4.69%, 10.09% and 1.49%, respectively. There were significantly positive correlations between catalase, sucrase and β-glucosidase activities and C3 derived HA and FA. The principal component analysis showed that catalase, sucrase and β-glucosidase were explained mainly by the first principal component indicating a significant correlation. These findings suggest that straw, compost and biochar are mainly sequestrated in Hu. Comparatively, the straw and compost are more likely to contribute to the formation of HA and FA in soil, but biochar favors the Hu, which helps in soil C sequestration. The formation of HA and FA derived from organic materials was supported by catalase, sucrase and β-glucosidase activities.

Different adsorption behaviors and mechanisms of a novel amino-functionalized hydrothermal biochar for hexavalent chromium and pentavalent antimony

A novel amino-functionalized hydrothermal biochar modified with nitric acid and nicotinamide (NMSH) was prepared and applied to remove heavy metal in different systems. The study of batch adsorption found that NMSH had different adsorption behaviors for Cr(VI) and Sb(V), and different concentrations of heavy metal ions exhibited different coadsorption behaviors in mixed system. NMSH had great anti-interference ability to coexisting inorganic ion and humic substance. The maximum adsorption capacity of NMSH was 132.74 mg/g for Cr(VI), and 241.92 mg/g for Sb(V). Moreover, different interfering ions and matter had different effects on adsorption. The mechanism study found that the adsorption mechanism of NMSH involved multiple interactions, and the mechanisms were different. Some O-containing functional groups of NMSH could reduce Cr(VI) to Cr(III), but not Sb(V). NMSH had great removal efficiency and reusability performance, which suggested that NMSH had prospects for practical wastewater treatment.

Eggshell-supported Catalysts for the Advanced Oxidation Treatment of Humic Acid Polluted Wastewaters

Metal nanoparticles have been reported as effective catalysts for the removal of refractory compounds from industrial wastewaters in advanced oxidation processes. Additionally, hundreds of thousands of tons of eggshells are discarded worldwide each year. In this work, this waste has been evaluated as support for the synthesis of nanomaterials by wet impregnation method. Four supported catalysts, with a load of iron or copper of 5% and 15%, were prepared and thoroughly characterized by means of different techniques (elemental analysis, XRF, XRD, FTIR, N2 adsorption-desorption, SEM, TEM and TGA). The catalysts performance was evaluated in wet oxidation tests to degrade humic acids, analyzing the evolution with time of COD, biodegradability index (BOD5/COD), color number and pH. The best results were achieved with 15% Cu and 5% Fe catalysts (COD reduction being 82.3% and 75.1%, respectively), whereas a COD reduction of 58% was obtained employing non-impregnated eggshell. This can be mainly attributed to the metal loading and the good metal distribution on the surface of the support. The BOD5 value of humic acids was initially null and, in all assays, the oxidation treatment enhanced the biodegradability. Therefore, eggshell has proved to be an interesting material to be employed as support in nanoparticles preparation.