Activation effect of catechol on biotic and abiotic factors of humus formation during chicken manure composting.

In this present study, catechol was added to promote humus formation in chicken manure composting using 12.5-L working volume lab-scale reactors. Chicken manure composting were carried out on two treatments, control (CK) and 0.5% (w/w) catechol treated group. Results showed that catechol addition reduced organic matter loss and improved the content of recalcitrant components. Humus and humic acid (HA) contents were, respectively, 69.2% and 82.3% higher in catechol treated-compost than in the control. With the addition of catechol, the bacterial community composition and richness was changed, e.g., the relative percentage of Bacillus and Sinibacillus were increased, which might contribute to humus and HA formation. Additionally, the activities of polyphenol oxidase and laccase (related to humus formation) were increased by the addition of catechol. Importantly, the catechol addition reduced the polyphenol content by 39.6% compared to control. Overall, the addition of catechol enhanced the biotic and abiotic factors to promote the humification process during composting, which might be a promising approach for accelerating the humification process and reducing contamination of phenolic compounds.

Effect of Maillard reaction on the formation of humic acid during thermophilic phase of aerobic fermentation.

This study aimed to explore the main pathway of humic acid (HA) formation during the thermophilic phase (TP) of aerobic fermentation, clarify the contribution of Maillard reaction. These experiments were carried out on cow dung, chicken manure and rice straw. Results indicated that the maximum temperature reached 60.2℃ during TP led to a sharp decrease in microbial abundance, while the production of HA increased. The network analysis indicated that microorganisms did not participate in the formation of HA and may be dominated by abiotic pathways. In addition, proteins and sugars were consumed at the highest rate during TP, and the trends were similar to HA formation. These findings suggested that the formation of HA has relationship to Maillard reaction, because TP provided suitable reaction conditions for Maillard reaction. Therefore, these results elucidated the contribution of Maillard reaction in HA formation during TP, and provided theoretical support for directional humification.

Effect of Fenton pretreatment combined with bacterial inoculation on humification characteristics of dissolved organic matter during rice straw composting.

The main purpose of this study was to explore the effects of Fenton pretreatment combined with bacterial inoculation on humification characteristics of dissolved organic matter (DOM) during rice straw composting. Three treatment groups (Fenton pretreatment: FeW, Fenton pretreatment and bacterial inoculation: FeWI, control: CK) were carried out during composting. The results showed that total organic carbon concentration of DOM and HIX showed an increase trend in all treatments in the composting process. The fungi that affect DOM conversion showed remarkable effects, meanwhile, fungal numbers of influencing DOM conversion were higher for FeWI than CK and FeW. The contribution rate of fungi to DOM was greater than that of environmental factors in FeWI composting, while environmental factors accounted for a large proportion in FeW and CK composting. This study exhibits referential significance for the effective degradation of agricultural wastes.

Effect of Fenton pretreatment and bacterial inoculation on cellulose-degrading genes and fungal communities during rice straw composting.

The aims of this article were to study the effect of Fenton pretreatment and bacterial inoculation on cellulose-degrading genes and fungal communities during rice straw composting. The rice straw was pretreated by Fenton reactions and functional bacterial agents were then inoculated during the cooling phase of composting. Three treatment groups were carried out, the control (CK), Fenton pretreatment (FeW) and Fenton pretreatment and bacterial inoculation (FeWI). The results indicated that Fenton pretreatment and bacterial inoculation changed the fungal communities composition and increased fungal diversity, leading to changes in the cellulose-degrading genes. In addition, a network analysis showed that in the FeWI treatment, the fungi from modules 1, 5 and 8 were core hosts of the cellulose-degrading genes driving the cellulosic degradation. Moreover, Fenton pretreatment and bacterial inoculation changed the core module fungal communities and strengthened the correlation between the core fungi and the cellulose-degrading genes, thereby promoting cellulosic degradation. Based on redundancy and structural equation model analyses, the NH4+-N, TOC, pH and Shannon index were important factors influencing the variations in the cellulose-degrading genes. This study provides a foundation for cellulosic degradation during cellulosic waste composting.

Core bacterial community driven the conversion of fulvic acid components during composting with adding manganese dioxide.

Here, we revealed the effects of microbes on fulvic acid (FA) formation in composting by adding MnO2. The results showed that the MnO2 promoted the formation of highly humified components (79.2% increased for component 2, and 45.8% increased for component 3) in FA. Additionally, core bacteria involved in FA transformation were identified, the MnO2 increased the relative abundance of core bacteria. Notably, two different core bacteria types were identified: "transforming bacteria" and "processing bacteria". The "transforming bacteria" dominated (about 40% contribution) in the formation of FA components with a high humification degree. The structural equation model confirmed that "transforming bacteria" could convert partly FA components with low humification into highly humified components, and the "transforming bacteria" could be regulated by environmental factors. These findings provided a new insight to manage FA humification degree during composting and helped to improve the application value of FA.

Identifying the role of exogenous amino acids in catalyzing lignocellulosic biomass into humus during straw composting.

This study was aimed at exploring the mechanism of promoting humus formation by the addition of exogenous amino acids. Amino acids not only participated in the synthesis of humus directly as precursors, but also changed the functions of bacterial communities. The composition and diversity of bacterial community changed with the addition of amino acids. The ability of bacterial community to degrade lignocellulose was enhanced, which provided precursors for humus synthesis. The key bacteria for humus formation and organic matter transformation were identified using random forests. These bacteria showed growth advantage with the addition of amino acids. The results showed that exogenous amino acids tended to transform organic matter and synthesize humus. Variance partitioning analysis confirmed that the bacterial community was the driving force of humus synthesis. These results were further verified by the structural equation model. These findings provided new ideas and understanding for straw waste composting.

δ-MnO2 changed the structure of humic-like acid during co-composting of chicken manure and rice straw.

Improving the structure and quantity of humus is important to reduce agriculture organic waste by composting. The present study was aimed to assess the role of δ-MnO2 on humus fractions formation during co-composting of chicken manure and rice straw. Two tests (control group (CK), the addition of δ-MnO2 (M)) were carried out. The results showed that organic matter content decreased by 34% and 29% at M and CK, suggesting the process of organic waste disposal was accelerated by adding δ-MnO2. The structures and quantity of fulvic acid (FA) and humic acid (HA) (as the main fractions of humus) were investigated. The δ-MnO2 had no significant effect on improving the concentration of FA and HA (p > 0.05). However, the addition of δ-MnO2 caused different effects on the FA and HA structure. The humification degree of FA improved, while bioavailability of HA increased through adding δ-MnO2. The addition of δ-MnO2 rephased the bacterial community structure, slowing down the succession rate of the bacterial community in M composting. After adding δ-MnO2, the structural equation modeling results showed that environmental factors could directly drive changes in FA and HA by modulating the bacterial community. Furthermore, the role of FA and HA in the soil amendment was also demonstrated. Therefore, the addition of MnO2 might be promising for agriculture organic waste treatment and environmental repair during composting.

Manganese dioxide driven the carbon and nitrogen transformation by activating the complementary effects of core bacteria in composting.

This study revealed core bacterial metabolic mechanisms involved in carbon (C) and nitrogen (N) in composting with adding MnO2. Two tests (control group (CK), adding MnO2 (M)) were performed. The results indicated that the MnO2 accelerated the transformation of carbon and nitrogen in composting. Core bacteria involved in the C and N conversion were identified, the complementarity effects of core bacteria were stimulated in M composting. Additionally, the influence of core bacteria on the C and N conversion could be divided into two pathways in M composting. One was that core bacteria promoted C and N conversion by accelerating the flow of amino acids into the tricarboxylic acid cycle. Another was that the complementarity effects of core bacteria increased the overall bacterial diversity, which contributed to C and N conversion. These findings showed that the addition of MnO2 to composting was a promising application to treat agricultural organic waste.

Effect of manganese dioxide on the formation of humin during different agricultural organic wastes compostable environments: It is meaningful carbon sequestration.

The study aims to accelerate the formation of humin (HM) with the addition MnO2 to achieve carbon sequestration during different material composting. The results indicated that the addition of MnO2 could improve the concentration of HM by increasing of the content in functional groups during corn straw (CS) and chicken manure (CM) composting. With the addition of MnO2, non-aromatic functional groups were responsible for the increase of the HM concentration in CM, while aromatic functional groups were dominating for CS. Although the formation mechanism of HM varied significantly across different materials, the MnO2 promoted more abundant functional groups to participate the formation of recalcitrant fluorescence components in CS and CM. In addition, the aromatization of HM structure was improved by adding the MnO2. Therefore, the addition of MnO2 not only increase carbon sequestration but also increase the compost product resilience during the decompose of agricultural organic wastes.

Effect of MnO2 on biotic and abiotic pathways of humic-like substance formation during composting of different raw materials.

The humic-like substances (HLS) are proposed to be formed by biotic and abiotic pathways. The abiotic pathways were neglected in existed composting studies. The present study aims to accelerate the abiotic pathways, and to investigate how MnO2 drives the HLS transformation via changing the contribution of abiotic and biotic pathways during composting with different materials. Parallel factor analysis model (PARAFAC), hetero two-dimensional correlation spectra (hetero-2DCOS) and variance partitioning were used to identify the effects of MnO2 on the formation of humic acid (HA) and fluvic acid (FA) during composting of chicken manure (CM) and corn straw (CS). The addition of MnO2 could change the structures of HLS during CS and CM composting, mainly promoting the formation of complex components in HA and FA during CS composting, as well as the complex components of FA during CM composting. Meanwhile, the addition of MnO2 could reshape the microbial ecology, which enhanced the correlation between microbes and complex components formation during composting, especially in CM composting. Variance partitioning showed that both abiotic and biotic pathways were stimulated in conversion of HLS components after adding MnO2 during CS composting, especially for the abiotic pathways. During CM composting, the MnO2 promoted biotic effects on the conversion of HLS components. Above all, the addition of MnO2 could stimulate pathways of biotic, abiotic or both of them to improve the humification degree of HLS by changing microbial ecology, which could be a promising way for promoting the application value of composting products.

Diversity in the Mechanisms of Humin Formation during Composting with Different Materials.

Humins (HMs) play a very important role in various environmental processes and are crucial for regulating global carbon and nitrogen cycles in various ecosystems. Composting is a controlled decomposition process accompanied by the stabilization of organic solid waste materials. During composting, active fractions of organic substances can be transformed into HMs containing stable and complex macromolecules. However, the structural heterogeneity and formation mechanisms of HMs during composting with various substrates have not been clarified. Here, the structure and composition of HMs extracted from livestock manure (LM) and straw (SW) during composting were investigated by excitation-emission matrices spectroscopy and Fourier transform infrared spectroscopy. The results showed that the stability and humification of LM-HM were lower than that of SW-HM. The parallel factor analysis components of the HM in LM composting contained the same fluorescent unit, and the intermediate of cellulose degradation affected the structure of the HM from SW composting. Structural equation modeling demonstrated that low-molecular-weight compounds were key factors in humification. On the basis of the structure and key factors impacting HM, we constructed two mechanisms for the formation of HM from different composting processes. The LM-HMs from different humification processes have multiple identical fluorescent structural units, and the high humification of SW is affected by its polysaccharide constituents, which contains a fluorescent component in their skeleton, providing a basis for studying HM in composting.

How does manganese dioxide affect humus formation during bio-composting of chicken manure and corn straw?

The aim of this study is to reveal the roles of MnO2 in Maillard reaction of biotic composting, and to identify its effectiveness in promoting humus formation. Corn straw (CS) and chicken manure (CM) have been chosen to be composted. During CS composting, addition of MnO2 rapidly reduced reducing sugars concentration (decreased by 84.0%) in 5 days and significantly improved humus production by 38.7% compared with treatment without MnO2. Whereas in CM composting, the promoting effect of MnO2 on humus formation was relatively weak by comparing with the treatment group of CS. Additionally, the presence of MnO2 has reshaped bacteria community, which might be the reason of MnO2 stimulated bacteria to utilize organic matter during CM composting. Therefore, the structural equation modeling has confirmed that MnO2 mainly performed as chemical catalyst to promote humus formation during CS composting. Besides catalyst, MnO2 also played as a bioactive activator in CM composting.

Identifying the key factors that affect the formation of humic substance during different materials composting.

The aim of this work was to identify the factors which can affect humic substance (HS) formation. Composting periods, HS precursors, bacteria communities and environment factors were recognized as the key factors and few studies explored the potential relationships among them. During composting, HS precursors were mainly formed in the heating and thermophilic phases, but HS were polymerized in the cooling and mature phases. Moreover, bacterial species showed similar classification of community structure in the same composting period of different materials. Furthermore, structural equation model showed that NH4--N and NO3--N were the indirect environmental factors for regulating HS formation by the bacteria and precursors as the indirect and direct driver, respectively. Therefore, both environmental factors and HS precursors can be the regulating factors to promote HS formation. Given that, a new staging regulating method had been proposed to improve the amount of HS during different materials composting.