The biotic effects of lignite on humic acid components conversion during chicken manure composting.

Targeted regulation of composting to convert organic matter into humic acid (HA) holds significant importance in compost quality. Owing to its low carbon content, chicken manure compost often requires carbon supplements to promote the humification progress. The addition of lignite can increase HA content through biotic pathways, however, its structure was not explored. The Parallel factor analysis revealed that lignite can significantly increase the complexity of highly humified components. The lignite addition improved phenol oxidase activity, particularly laccase, during the thermophilic and cooling phases. The abundance and transformation functions of core bacteria also indicated that lignite addition can influence the activity of microbial transformation of HA components. The structural equation model further confirmed that lignite addition had a direct and indirect impact on enhancing the complexity of HA components through core bacteria and phenol oxidase. Therefore, lignite addition can improve HA structure complexity during composting through biotic pathways.

Applications of humic and fulvic acid under saline soil conditions to improve growth and yield in barley.

BACKGROUND: Enriching the soil with organic matter such as humic and fulvic acid to increase its content available nutrients, improves the chemical properties of the soil and increases plant growth as well as grain yield. In this study, we conducted a field experiment using humic acid (HA), fulvic acid (FA) and recommended dose (RDP) of phosphorus fertilizer to treat Hordeum vulgare seedling, in which four concentrations from HA, FA and RDP (0.0 %, 50 %, 75 % and 100%) under saline soil conditions . Moreover, some agronomic traits (e.g. grain yield, straw yield, spikes weight, plant height, spike length and spike weight) in barley seedling after treated with different concentrations from HA, FA and RDP were determined. As such the beneficial effects of these combinations to improve plant growth, N, P, and K uptake, grain yield, and its components under salinity stress were assessed. RESULTS: The findings showed that the treatments HA + 100% RDP (T1), HA + 75% RDP (T2), FA + 100% RDP (T5), HA + 50% RDP (T3), and FA + 75% RDP (T6), improved number of spikes/plant, 1000-grain weight, grain yield/ha, harvest index, the amount of uptake of nitrogen (N), phosphorous (P) and potassium (K) in straw and grain. The increase for grain yield over the control was 64.69, 56.77, 49.83, 49.17, and 44.22% in the first season, and 64.08, 56.63, 49.19, 48.87, and 43.69% in the second season,. Meanwhile, the increase for grain yield when compared to the recommended dose was 22.30, 16.42, 11.27, 10.78, and 7.11% in the first season, and 22.17, 16.63, 11.08, 10.84, and 6.99% in the second season. Therefore, under salinity conditions the best results were obtained when, in addition to phosphate fertilizer, the soil was treated with humic acid or foliar application the plants with fulvic acid under one of the following treatments: HA + 100% RDP (T1), HA + 75% RDP (T2), FA + 100% RDP (T5), HA + 50% RDP (T3), and FA + 75% RDP (T6). CONCLUSIONS: The result of the use of organic amendments was an increase in the tolerance of barley plant to salinity stress, which was evident from the improvement in the different traits that occurred after the treatment using treatments that included organic amendments (humic acid or fulvic acid).

Inhibitory effects and mechanisms of insoluble humic acids on internal phosphorus release from the sediments.

Release of phosphorus (P) from the sediments plays a critical role in the eutrophication of aquatic environments. Humic acids (HA), as the main form of carbon storage in the sediments, has essential impacts on the biogeochemical cycle of phosphorus in aquatic systems. Nevertheless, previous studies mainly concentrated on the competitive adsorption of HA solution and P on metal oxides and soils, with little attention paid to the effects of insoluble humic acids (IHA) on P sorption by and release from the sediments. Herein, an investigation on the rivers and lakes in Sichuan Province, China, found that there was a significantly positive correlation between the maximum P adsorption capacity (Qmax) of sediments and IHA contents (p < 0.01), but a significantly negative correlation between the zero equilibrium P concentration (EPC0) and IHA concentrations (p < 0.01). This indicated that IHA might have an inhibitory effect on the release of P from the sediments, which was verified by batch adsorption experiments and static incubation experiments. Adsorption experiments indicated that IHA can promote P adsorption by sediments. With the increase of IHA addition (from 0 to 20 mg/g) in the sediments, Qmax of sediments increased (from 0.516 to 0.911 mg/g), while EPC0 decreased greatly (from 0.264 to 0.005 mg/L). Increases in Fe (Ⅲ) bound-P, Al bound-P and humic bound-P caused by IHA were responsible for this promoting effect. Incubation experiments illustrated that IHA addition can efficiently inhibit P release from the sediments. After 32 days incubation, P concentration in the overlying water of control group (without IHA addition) was 0.651 mg/L, which was 13.29-40.69 times higher than those (0.016-0.049 mg/L) in the test groups (with 5 %-20 % IHA addition). The analysis of P species in sediments showed that transformation from loosely adsorbed-P and Fe (Ⅲ) bound-P to Al bound-P and humic bound-P was responsible for this inhibition of P release by IHA. This study demonstrated that IHA, differing from readily degradable or dissolved organic matter, have great inhibitory effects on internal P release, which provided a novel insight into the association between carbon burial and internal P release and even the management of water eutrophication.

Spatiotemporal evolution of dissolved organic matter (DOM) and its response to environmental factors and human activities.

The South-to-North Water Diversion East Project (SNWDP-E) is an effective way to realize the optimal allocation of water resources in China. The North Dasha River (NDR) is the reverse recharge section that receives water from the Yufu River to the Wohushan Reservoir transfer project line in the SNWDP. However, the dissolved organic matter (DOM) evolution mechanism of seasonal water transfer projects on tributary waters has not been fully elucidated. In this paper, the NDR is the main object, and the changes in the composition and distribution of spectral characteristics during the winter water transfer period (WT) as well as during the summer non-water transfer period (NWT) are investigated by parallel factor analysis (PARAFAC). The results showed that the water connectivity caused by water transfer reduces the environmental heterogeneity of waters in the basin, as evidenced by the ammonia nitrogen (NH4+-N) and total phosphorus (TP) in the water body were significantly lower (p<0.05, p<0.01) during the water transfer period than the non-water transfer period. In addition, the fluorescence intensity of DOM was significantly lower in the WT than the NWT (p<0.05) and was mainly composed of humic substances generated from endogenous sources with high stability. While the NWT was disturbed by anthropogenic activities leading to significant differences in DOM composition in different functional areas. Based on the redundancy analysis (RDA) and multiple regression analysis, it was found that the evolution of the protein-like components is dominated by chemical oxygen demand (COD) and NH4+-N factors during the WT. While the NWT is mainly dominated by total nitrogen (TN) and TP factors for the evolution of the humic-like components. This study helps to elucidate the impact of water transfer projects on the trunk basin and contribute to the regulation and management of inter-basin water transfer projects.

Halophyte Elymus dahuricus colonization regulates microbial community succession by mediating saline-alkaline and biogenic organic matter in bauxite residue.

Alkalinity regulation and nutrient accumulation are critical factors in the construction of plant and microbial communities and soil formation in bauxite residue, and are extremely important for sustainable vegetation restoration in bauxite residue disposal areas. However, the establishment and succession of microbial communities driven by plant colonization-mediated improvements in the physicochemical properties of bauxite residues remain poorly understood. Thus, in this study, we determined the saline-alkali properties and dissolved organic matter (DOM) components under plant growth conditions and explored the microbial community diversity and structure using Illumina high-throughput sequencing. The planting of Elymus dahuricus (E. dahuricus) in the bauxite residue resulted in a significant decrease in total alkalinity (TA), exchangeable Na, and electrical conductivity (EC) as well as the release of more tryptophan-like protein compounds and low-molecular-weight humic substances associated with biological activities into the bauxite residue substrate. Taxonomical analysis revealed an initial-stage bacterial and fungal community dominated by alkaline-tolerant Actinobacteriota, Firmicutes, and Ascomycota, and an increase in the relative abundances of the phyla Bacteroidota, Cyanobacteria, Chloroflexi, and Gemmatimonadota. The biological activities of phylum Actinobacteriota, Bacteroidota, and Gemmatimonadota were significantly associated with protein-like and UVA-like humic substances. As eutrophic bacteria, Proteobacteria participate in the transformation of humic substances and can not only utilize small molecules of organic matter and convert them into humic substances but also promote the gradual conversion of humic acids into simple molecular compounds. Our results suggest that plant roots secrete organic matter and microbial metabolites as the main biogenic organic matter that participates in the establishment and succession of the microbial community in bauxite residues. Root length affects bacterial and fungal diversity by mediating the production of protein-like substances.

Potential linkage between WWTPs-river-integrated area pollution risk assessment and dissolved organic matter spectral index.

The direct discharge of wastewater can cause severe damage to the water environment of the surface water. However, the influence of dissolved organic matter (DOM) present in wastewater on the allocation of DOM, nitrogen (N), and phosphorus (P) in rivers remains largely unexplored. Addressing the urgent need to monitor areas affected by direct wastewater discharge in a long-term and systematic manner is crucial. In this paper, the DOM of overlying water and sediment in the WWTPs-river-integrated area was characterized by ultraviolet-visible absorption spectroscopy (UV-vis), three-dimensional excitation-emission matrix combined with parallel factor (PARAFAC) method. The effects of WWTPs on receiving waters were investigated, and the potential link between DOM and N, P pollution was explored. The pollution risk was fitted and predicted using a spectral index. The results indicate that the improved water quality index (IWQI) is more suitable for the WWTPs-river integration zone. The DOM fraction in this region is dominated by humic-like matter, which is mainly influenced by WWTPs drainage as well as microbial activities. The DOM fractions in sediment and overlying water were extremely similar, but fluorescence intensity possessed more significant spatial differences. The increase in humic-like matter facilitates the production and preservation of P and also inhibits nitrification, thus affecting the N cycle. There is a significant correlation between DOM fraction, fluorescence index, and N, P. Fluorescence index (FI) fitting of overlying water DOM predicted IWQI and trophic level index, and a(254) fitting of sediment DOM predicted nitrogen and phosphorus pollution risk (FF) with good results. These results contribute to a better understanding of the impact of WWTPs on receiving waters and the potential link between DOM and N and P pollution and provide new ideas for monitoring the water environment in highly polluted areas.

Developing a Compost Quality Index (CQI) Based on the Electrochemical Quantification of Cd (HA) Reactivity.

The present work demonstrates the use of Cd2+ as a reactivity probe of the fulvic acids (FAs), humic acids (HAs) and dissolved organic matter (DOM) compost extracts. Significant differences were observed between the extracts, with the HA extract showing the highest reactivity. Comparing the different composts, the largest reactivity variation was again observed for HA then FA and finally DOM extracts. The Cd2+ binding extent was used to calculate the quality of composts and compared with a reference of uncomposted organic fertiliser (FLW), leading to the definition of an operational scale of compost quality. The parameter equivalent mass of fertiliser (mEF) was used for this scale sorted the seven composts from 0.353 to 1.09 kg FLW, for compost of sewage sludge (CSS) and vermicompost of domestic waste (CVDW), respectively. The significance of this parameter was verified through a correlation analysis between binding extent and the effect of compost application on lettuce crop growth in a field trial. The results demonstrate the potentiality of FA and HA extracts as markers of compost bioactivity and the use of Cd2+ as a reactivity probe.

Influence of thermal air oxidation on the chemical composition and uranium binding property of intrinsic dissolved organic matter from biochar.

In this work, uranium (U(VI)) binding characteristics of the intrinsic dissolved organic matters (DOM) from the biochars prepared under thermal air oxidation (TAO) and non-TAO conditions were studied using synchronous fluorescence spectra (SFS) and Fourier transform infrared (FTIR) in conjunction with the general two-dimensional correlation spectroscopy (2D-COS), heterospectral 2D-COS and moving-window (MW) 2D-COS. The chemical compositions of the intrinsic DOMs from biochars with/without TAO were investigated by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). Results showed that the preferential binding of U(VI) to functional groups followed the order: 937 (carboxyl γC-OH), 981 (carboxyl γC-OH), 1511 (aromatic vC = C), 1108 (esters or ethers vC-O), 1282 (esters or carboxyl vC-O), 1698 (saturated carboxylic acid or ketone vC = O) cm-1 for biochar DOM after TAO (OB600), and 937 (carboxyl γC-OH), 1484 (lipids δC-H or phenolic vC-O), 1201 (esters or carboxyl vC-O), 1112 (esters or ethers vC-O), 1706 (saturated aldehyde, carboxylic acid or ketone vC = O), 1060 (phenolic, esters or ethers vC-O), 1014 (phenolic, esters or ethers vC-O) cm-1 for the pristine biochar (B600). Fulvic-like substances at 375 nm in the biochar DOM showed a preferential binding with U(VI) after TAO, while humic-like substances played a more critical role in the U(VI) complexation with biochar DOM obtained from non-TAO condition. The results also indicated that TAO increased the content of fluorescent DOM and the chemical stability of DOM-U(VI) complexes. The FT-ICR MS results showed an increase in the relative abundance of protein-like, carbohydrates-like, tannins-like, unsaturated hydrocarbons, and condensed aromatic structure and a decrease in the relative abundance of lipid-like and lignin-like after TAO. Consequently, although biochar after TAO had a much poorer content of intrinsic DOM, its intrinsic DOM showed a much higher capacity in U(VI) precipitation. Therefore, the TAO substantially changed the chemical composition, binding property and environmental behavior of intrinsic DOM from biochar.

Two recyclable and complementary adsorbents of coal-based and bio-based humic acids: High efficient adsorption and immobilization remediation for Pb(II) contaminated water and soil.

Humic acid can effectively bind heavy metals and is a promising remediation agent for heavy metals-contaminated water and soil. Many successful applications of humic acid have been reported, but rarely studied the specific process and mechanism of heavy metal removal by humic acids from water and soil, especially the simultaneous application of coal-based and bio-based humic acids. In this work, two kinds of coal-based and bio-based humic acid materials (CHA and BHA) from weathered coal and rice husk were industrially produced and studied their Pb(II) adsorption and immobilization characteristics and mechanisms in water and soil. The batch adsorption experiments obtained the Pb(II) adsorption by CHA and BHA both were spontaneous and endothermic monolayer chemisorption and controlled by three rate-limiting steps (bulk, film, and pore) in the adsorption process. CHA and BHA had highly efficient Pb(II) adsorption capacities, obtained their maximum adsorption capacity was 201 and 188 mg g-1, respectively. In addition to the two main adsorption mechanisms of ion exchange and surface complexation, electrostatic interaction, precipitation reaction, and π-π interaction were also involved. Soil culture experiments showed that CHA and BHA both exhibited a highly efficient immobilization effect on Pb(II)-contaminated soil, and CHA and BHA had a better synergistic promotion effect. Compared with the CK soil, the content of DTPA-Pb(II) decreased by 10.2-13.2% and the content of RES-Pb(II) increased by 14-22% in soils treated with different humic acids. Ion exchange, complexation, precipitation, and electrostatic attraction promote the transformation of unstable Pb(II) to stable Pb(II), which was of great significance for the immobilization of Pb(II) in soil. Overall, CHA and BHA have the potential to be used as green, efficient, and promising adsorbents to remove and immobilize Pb(II) from wastewater and soil.

Reactive oxygen species accelerate humification process during iron mineral-amended sludge composting.

The production of hydroxyl radicals (OH) has been documented during composting. However, the effect of OH on composting efficiency remains unclear. Here, iron mineral supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing OH production and accelerating the maturation of composting. The results indicated that the maximum OH production of imTC was 1922.74 µmol·kg-1, which increased by 1.39 times than that of ordinary thermophilic composting (oTC). Importantly, the increase of OH could greatly enhance organic matter degradation and humic substances formation during imTC, resulting in shorting the maturity time by 25 %. Enrichment of laccase-producing bacteria resulted in higher laccase activity (31.85 U·g-1) in imTC compared with oTC (23.82 U·g-1), which may have contributed to the higher level of humification in imTC treatment. This work, for the first time, proposes a feasible strategy for improving composting efficiency through the regulation of OH production during aerobic composting.

Humic acid and phosphorus fractions transformation regulated by carbon-based materials in composting steered its potential for phosphorus mobilization in soil.

This study investigated the effects of different carbon-based additives including biochar, woody peat, and glucose on humic acid, fulvic acid, and phosphorus fractions in chicken manure composting and its potential for phosphorus mobilization in soil. The results showed that the addition of glucose effectively increased the total humic substance content (90.2 mg/g) of composts, and the fulvic acid content was significantly higher than other groups (P < 0.05). The addition of biochar could effectively improve the content of available phosphorus by 59.9% in composting. The addition of carbon-based materials to the composting was beneficial for the production of more stable inorganic phosphorus in the phosphorus fraction. The highest proportion of soluble inorganic phosphorus components of sodium hydroxide was found in group with woody peat addition (8.7%) and the highest proportion of soluble inorganic phosphorus components of hydrochloric acid was found in group with glucose addition (35.2%). The compost products with the addition of biochar (humic acid decreased by 17.9%) and woody peat (fulvic acid decreased by 72.6%) significantly increased soil humic acid mineralization. The compost products with the addition of biochar was suitable as active phosphate fertilizer, while the compost products with the addition of glucose was suitable as slow-release phosphate fertilizer.

Prospects for humic acids treatment and recovery in wastewater: A review.

Clean water shortages require the reuse of wastewater. The presence of organic substances such as humic acids in wastewater makes the water treatment process more difficult. Humic acids can significantly affect the removal of heavy metals and other such toxins. Humic acids is formed by the decomposition and transformation of animal and plant remains by microorganisms, and naturally exists in soil and water. It is necessary to degrade and remove humic acids from wastewater. As it seriously human health, effective technologies for removing humic acids from wastewater have attracted great interest over the past decades. This study compared existing techniques for removing humic acids from wastewater, as well as their limitations. Physicochemical treatments including filtration and oxidation are basic and key approaches to removing humic acids. Biological treatments including enzyme and fungi-mediated humic acids degradation are economically feasible but require some scalability. In conclusion, the integrated treatment processes are more significant options for the effective removal of humic acids from wastewater. In addition, humic acids have rich utilization values. It can improve the soil, increase crop yields, and promote the removal of pollutants.

Resin-based iron-manganese binary oxide for phosphate selective removal.

Adsorption technology can effectively remove phosphorus from water and realize phosphorus recovery. Hence, it is used to curb the eutrophication of water and alleviate the crisis caused by the shortage of phosphorus resources. Resin has been attracting increasing interest as an ideal adsorption material; however, its practical application is greatly affected by environmental factors. To solve the competitive adsorption and pore blockage caused by humic acid and coexisting ions during the removal of phosphorus by ion-exchange resin, this study has developed an iron-manganese oxide-modified resin composite adsorbent (Fe/Mn-402) based on the nanoconfinement theory. The structural characterization results of XRD, FT-IR, SEM, and XPS showed that the iron-manganese binary oxide was successfully loaded on the skeleton of the strongly alkaline anion resin and showed good stability under both neutral and alkaline conditions. The batch adsorption experiments showed that the maximum adsorption capacity of Fe/Mn-402 for phosphorus can reach up to 50.97 mg g-1 under the optimal raw material ratio (Fe:Mn = 1:1). In addition, Fe/Mn-402 shows good selectivity for phosphorus removal. Fe/Mn-402 can maintain good adsorption performance for phosphate even under high concentrations of SO42-, HCO3-, and humic acid. The regenerated Fe/Mn-402 can be recycled without any obvious change in its treatment capacity. Hence, it is suitable for stable, long-term usage. In general, this work puts forward a new idea for the development of phosphorus-removal adsorbents for the treatment of wastewater containing coexisting ions and HA.

Biosynthesis of MnFe2O4@TiO2 magnetic nanocomposite using oleaster tree bark for efficient photocatalytic degradation of humic acid in aqueous solutions.

The presence of humic acid compounds in water resources, as one of the precursors of Trihalomethanes and Holoacetic acids, causes health problems for many communities. The aim of this research study was to investigate the photocatalytic degradation efficiency of humic acid using MnFe2O4@TiO2 nanoparticles which produced by green synthesis method. The synthesis of metal nanoparticles using plant extracts and the study of their catalytic performance is a relatively new topic. Many chemical techniques have been proposed for the synthesis of MnFe2O4@TiO2 nanoparticles, but green synthesis has received much attention due to its availability, simplicity, and non-toxicity. The properties of synthesized nanoparticles were determined by SEM, FT-IR, XRD, EDS, and DLS analysis. The results of the study showed that under optimal experimental conditions (pH = 3, nanocomposite dose = 0.03 g/L, humic acid initial concentration = 2 mg/L, and contact time = 20 min), it is possible to achieve maximum degradation of humic acid. Therefore; MnFe2O4@TiO2 nanoparticles have high efficiency for removing of humic acid from aqueous solutions under UV light.

[Effects of Soil Amendments on the Bacterial Diversity and Abundances of Pathogens and Antibiotic Resistance Genes in Rhizosphere Soil Under Drip Irrigation with Reclaimed Water].

Due to reclaimed water, irrigation can cause human health and environmental risks. Soil amendments are applied to reveal the abundance of pathogens and antibiotic resistance genes in rhizosphere soil irrigated by reclaimed water and to better understand the effects of environmental factors on the rhizosphere soil bacterial composition, which has guiding significance for the reasonable use of soil amendments. In this study, the effects of biochar, bioorganic fertilizer, humic acid, loosening soil essence, and corn vinasse on bacterial community diversity and certain gene abundances in rhizosphere soil under drip irrigation with reclaimed water were studied using high-throughput assays and quantitative PCR. The results showed that biochar significantly increased pH, organic matter, and total nitrogen contents in the rhizosphere soil. The corn vinasse significantly decreased soil pH and increased the contents of total nitrogen and total phosphorus but significantly increased the soil EC value (P<0.05). The effects of the five soil amendments on the α-diversity of rhizosphere bacteria were not significantly different. The bacterial community structure and diversity of rhizosphere bacteria were similar at different taxonomic levels, but their relative abundance was different. α-Proteobacteria, γ-Proteobacteria, Bacteroidia, Actinobacteria, Acidimicrobiia, and Anaerolineae were the dominant bacteria in all treatments. The dominant genera consisted of Pseudomonas, Sphingobium, Sphingomonas, Cellvibrio, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Flavobacterium, and Algoriphagus (relative abundance>1%). Correlation analysis of environmental factors showed that the composition of the rhizosphere bacterial community was strongly correlated with pH, EC, total nitrogen, and total phosphorus content. The abundances of pathogenic bacteria and antibiotic resistance genes were 103-107 copies·g-1 and 104-108 copies·g-1, respectively. There were significant differences in the detection levels of pathogens and antibiotic resistance genes. Bioorganic fertilizer, loosening soil essence, and corn vinasse significantly increased the abundances of some antibiotic resistance genes, whereas humic acid and corn vinasse significantly decreased the abundances of Pseudomonas syringae, Ralstonia solanacearum, and total coliforms (P<0.05). A significant correlation was found between pathogens (Arcobacter, Bacillus cereus, Pantoea agglomerans, and Fecal bacteroidetes) and antibiotic resistance genes (tetA, tetB, tetO, tetQ, sul1, ermB, and ermC). In conclusion, while monitoring pathogens and antibiotic resistance genes in the agricultural environment under reclaimed water irrigation, attention should be paid to the rational application of soil amendments to avoid exacerbating the spread of biological contamination.

Effect of humic acid derived from leonardite on the redistribution of uranium fractions in soil.

Humic acids (HAs) are complex organic substances with abundant functional groups (e.g., carboxyl, phenolic-OH, etc.). They are commonly distributed in the soil environment and exert a double-edged sword effect in controlling the migration and transformation of uranium. However, the effects of HAs on dynamic processes associated with uranium transformation are still unclear. In this study, we used HAs derived from leonardite (L-HA) and commercial HA (C-HA) as exogenous organic matter and C-HA as the reference. UO2, UO3, and UO2(NO3)2 were used as the sources of U to explore the fractionations of uranium in the soil. We also studied the behavior of the HA. The incubation experiments were designed to investigate the effects of HA on the soil pH, uranium fraction transformation, dynamic behavior of exchangeable, weak acid, and labile uranium. The observations were made for one month. The results showed that soil pH decreased for L-HA but increased for C-HA. Under these conditions, uranium tended to transform into an inactive fraction. The dynamic behavior of exchangeable, weak acid, and labile uranium varied with the sources of HA and uranium. This study highlighted that HA could affect soil pH and the dynamic redistribution of U fractions. The results suggest that the sources of HA and U should be considered when using HA as the remediation material for uranium-contaminated soils.

Characteristics of soil CO2 emission and ecosystem carbon balance in wheat-maize rotation field with 4-year consecutive application of two lignite-derived humic acids.

Humic acid originating from lignite is a popular resource of organic fertilizer. The effects of humic acid application on crop biomass and soil CO2 emission charged the regional agro-ecosystem carbon balance. Two kinds of humic acid, obtained from lignite via H2O2-oxidation (OHA) and KOH-activation (AHA), were applied in a wheat-maize rotation located field at three levels of 500 (OHA1; AHA1), 1000 (OHA2; AHA2), and 1500 kg hm-2 (OHA3; AHA3), only chemical fertilizer treatment (CF) as control to investigate the change of soil CO2 emission, crop yield and ecosystem carbon balance in 2016-2019. During the four experimental years, the trend of cumulative efflux of soil CO2 was increasing in medium and high dosage humic acid treatments. The grain yield of wheat and maize had the same trend as the cumulative efflux of soil CO2 due to the increase of soil NO3--N and soil available P directly affected by humic acid application. The main factor of cumulative soil CO2 efflux improvement was soil NO3--N and soil available P in 2016, while soil available potassium became key factor in 2019 with the step regression. Net ecosystem productivity (NEP) was used to assess ecosystem carbon balance, which was positive values showed atmospheric CO2 sink under all the fertilization treatments and increased with the increase of humic acid use level. AHA2 and AHA3 treatments charged the higher NEP in 2019 than 2016. Meanwhile, AHA treatment presented a higher NEP average than OHA treatment with the same applied level. Crop yield and soil available P was the directly positive factor to NEP over four years under the fertilization by SEM analysis. It is recommended that AHA be applied at 1000 kg hm-2 together with chemical fertilizers to achieve the higher crop yield and a sink of the atmospheric CO2 in agricultural fields in North China.

Study on the effect of Cr(VI) removal by stimulating indigenous microorganisms using molasses.

Molasses have a prominent effect on the bioremediation of Cr(VI) contaminated groundwater. However, its reaction mechanism is not detailed. In this paper, the removal of Cr(VI) with different carbon sources was compared to explore the effect and mechanism of the molasses. The addition of molasses can completely remove 25 mg/L Cr(VI), while the removal efficiency by glucose or emulsified vegetable oil was only 20%. Molasses could rapidly stimulate the reduction of Cr(VI) by indigenous microorganisms and weakened the toxicity on bacteria. The average removal rate of Cr(VI) was 0.42 mg/L·h, 10 times that of glucose system. Compared with glucose, molasses can remediate Cr(VI) at a higher concentration (50 mg/L), and the carbohydrate acted as microbial nutrients. Direct and indirect reduction acted together, the Fe(II) content in the aquifer medium increased from 1.7% to 4.7%. The addition of molasses extract into glucose system could increased the removal rate of Cr(VI) by 2-3 times, and the ions of molasses had no significant effect on the reduction. Excitation emission matrix fluorescence spectra and electrochemical analysis proved that the molasses contained humic acid-like substances, which had the ability of electron shuttle and improved the reduction rate of Cr(VI). In the process of bioreduction, the composition of molasses changed and the electron transport capacity increased from 104.2 to 446.5 µmol/(g C), but these substances could not be used as electron transport media to continuously enhance the reduction effect. This study is of great significance to fully understand the role and application of molasses.

Water quality and periphyton functional response to input of dissolved manure-derived hydrochars (DHCs).

Dissolved organic matter (DOM) plays a critical role in the global carbon cycle and provides food and energy for aquatic organisms. Recently, hydrochar, as a solid carbonaceous substance derived from hydrothermal carbonization, has been increasingly used as a soil amendment. Upon entering the soil, dissolved components (DHCs) were released from hydrochar as exogenous DOM, finally entering the aquatic ecosystems by runoff, which participates in environmental geochemical processes. However, relevant reports revealing the response of the aquatic ecosystem to the input of DHCs remain insufficiently elucidated. For the first time, the fundamental features of DHCs and their influence on water quality and aquatic biological function were investigated in this study. DHCs at 260 °C (DHC260) had lower yields, a greater [C/N], worse biodegradability, and larger humic acid relative amounts than did DHCs at 180 °C (DHC180). The DHC structural alterations in periphyton-incubated aquatic ecosystems suggested that protein substances were more easily degraded or assimilated by periphyton, especially for DHC180, with rates of decrease of 34.5-63.5%. The increased chemical oxygen demand (COD) degradation in the DHC260 treatments was most likely due to humic acid substances with higher COD equivalents. Furthermore, DHC260 caused phosphorus to accumulate in periphyton, reducing aquatic phosphorus concentration. Notably, the abundances of Flavobacteria and Cyanobacteria associated with water blooms increased 12.7-25.5- and 1.3-8.3-fold, respectively; consequently, the promotional impact of DHCs on algal blooms should be considered. This result extends the nonnegligible role of DHCs in aquatic ecosystems and underlines the need to regulate the hydrochar application process.

Performance assessment of in-vessel composter through heavy metal immobilization and humification of Parthenium hysterophorus.

The bioconversion of Parthenium hysterophorus was performed through rotary drum composter and examined the mechanism of humification and heavy metals immobilization in the process. The 20th day compost contains a significant increase in humic substances of 28.7% compared to the initial day mix. The bioavailable fractions of heavy metals have reduced by 30 to 55% in the 20th day compost compared to the initial day mix. The leaching potential of cadmium has been reduced by 69% in the 20th day compost. The immobile fractions (F5) of Cd, Ni and Pb have been increased to 100, 99 and 78% in the 20th day compost. The mitotic index was increased by 1.7 and 51.6% in 25% dosed compost extract compared to the control and P. hysterophorus extract respectively. The transition of heavy metals to immobile fraction indicated the biodegradation capability of P. hysterophorus through rotary drum composting.