Performance of microbial inoculation and tricalcium phosphate on nitrogen retention and conversion: Core microorganisms and enzyme activity during kitchen waste composting.

The substantial release of NH3 during composting leads to nitrogen (N) losses and poses environmental hazards. Additives can mitigate nitrogen loss by adsorbing NH3/NH4, adjusting pH, and enhancing nitrification, thereby improving compost quality. Herein, we assessed the effects of combining bacterial inoculants (BI) (1.5%) with tricalcium phosphate (CA) (2.5%) on N retention, organic N conversion, bacterial biomass, functional genes, network patterns, and enzyme activity during kitchen waste (KW) composting. Results revealed that adding of 1.5%/2.5% (BI + CA) significantly (p < 0.05) improved ecological parameters, including pH (7.82), electrical conductivity (3.49 mS/cm), and N retention during composting. The bacterial network properties of CA (265 node) and BI + CA (341 node) exhibited a substantial niche overlap compared to CK (210 node). Additionally, treatments increased organic N and total N (TN) content while reducing NH4+-N by 65.42% (CA) and 77.56% (BI + CA) compared to the control (33%). The treatments, particularly BI + CA, significantly (p < 0.05) increased amino acid N, hydrolyzable unknown N (HUN), and amide N, while amino sugar N decreased due to bacterial consumption. Network analysis revealed that the combination expanded the core bacterial nodes and edges involved in organic N transformation. Key genes facilitating nitrogen mediation included nitrate reductase (nasC and nirA), nitrogenase (nifK and nifD), and hydroxylamine oxidase (hao). The structural equation model suggested that combined application (CA) and microbial inoculants enhance enzyme activity and bacterial interactions during composting, thereby improving nitrogen conversion and increasing the nutrient content of compost products.

Adsorption of humic acid from different organic solid waste compost to phenanthrene, is fluorescence excitation or quenching?

Humic acid (HA) from different organic solid waste (OSW) compost has been shown good adsorption properties for phenanthrene. However, the raw material of HA can affect its structure, resulting in differences in adsorption capacity. Therefore, this study focused on the adsorption characteristics of phenanthrene by HA from different OSW compost. In this work, chicken manure (CM), rice straw (RS) and lawn waste (LW) were selected as sources of composted HA. The adsorption mechanism of HA from different OSW compost were revealed through analytical techniques including three-dimensional fluorescence spectroscopy (EEM), two-dimensional correlation spectroscopy (2DCOS), and Fourier-transform infrared spectroscopy (FTIR). The results suggested that HA from LW compost had a better adsorption affinity for phenanthrene because of its more complex fluorescent component, where C1 as a simple component determined the adsorption process specifically. Furthermore, after HA from LW compost adsorbed phenanthrene, the increase in aromatic -COOH and -NH was the main reason for fluorescence quenching. These results indicated that HA from LW compost had better adsorption effect for phenanthrene. The results of this study were expected to provide a selection scheme for the control of phenanthrene pollution and environmental remediation.

Greenhouse gas emission characteristics during kitchen waste composting with biochar and zeolite addition.

Aerobic kitchen waste composting can contribute to greenhouse gas (GHGs) emissions and global warming. This study investigated the effects of biochar and zeolite on GHGs emissions during composting. The findings demonstrated that biochar could reduce N2O and CH4 cumulative releases by 47.7 %and 47.9 %, respectively, and zeolite could reduce the cumulative release of CO2 by 28.4 %. Meanwhile, the biochar and zeolite addition could reduce the abundance of potential core microorganisms associated with GHGs emissions. In addition, biochar and zeolite reduced N2O emissions by regulating the abundance of nitrogen conversion functional genes. Biochar and zeolite were shown to reduce the impact of bacterial communities on GHGs emissions. In summary, this study revealed that biochar and zeolite can effectively reduce GHG emissions during composting by altering the compost microenvironment and regulating microbial community structure. Such findings are valuable for facilitating high-quality resource recovery of organic solid waste.

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.

The positive effect of the enzyme inducer (MnSO4) on the formation of humic substance in rice straw composting by stimulating key microorganisms.

This study investigated the impact of adding enzyme inducer (MnSO4) on humic substance (HS) formation during straw composting. The results demonstrated that both enzyme inducer treatment group (Mn) and functional microorganism treatment group (F) led to an increase in the content of HS compared to the treatment group without enzyme inducer and functional microorganism (CK). Interestingly, the enzyme inducer exhibited a higher promoting effect on HS (57.80 % ~ 58.58 %) than functional microbial (46.54 %). This was because enzyme inducer stimulated the growth of key microorganisms and changed the interaction relationship between microorganisms. The structural equation model suggested that the enzyme inducer promoted the utilization of amino acids by the fungus and facilitated the conversion of precursors to humic substance components. These findings provided a direction for improving the quality of composting products from agricultural straw waste. It also provided theoretical support for adding MnSO4 to compost.

Effect of Maillard reaction based on catechol polymerization on the conversion of food waste to humus.

The pollution and harm of food waste (FW) are increasingly concerned, which has the dual attributes of pollutants and resources. This study aimed to improve the synthesis efficiency of FW humic substances (HS), and investigating the effect of catechol on the formation mechanism and structure of humic acid (HA) and fulvic acid (FA). Results indicated that catechol incorporation could enable to exhibit higher HS yield and more complex structure, especially the maximum particle size of FA reached 4800 nm. This was due to the combination of catechol with multiple nitrogenous compounds, which accelerated molecular condensation. Spectroscopic scans analysis revealed that Maillard reaction occurs first. Subsequently, Maillard reaction products and amino acids were combined with different sites of catechol, which leads to the difference of molecular structure of HS. The structure of FA is characterized by an abundance of carboxyl and hydroxyl groups, whereas HA is rich in benzene and heterocyclic structures. The structural difference was responsible for the disparity in the functional properties of FA and HA. Specifically, the presence of amino, hydroxyl, pyridine, and carboxyl groups in FA contributes significantly to its chelating activity. This research provides an efficient and sustainable unique solution for the high-value of FW conversion, and provides evidence for understanding the structural evolution of HA and FA.

Optimization of organic solid waste composting process through iron-related additives: A systematic review.

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Malonic acid shapes bacterial community dynamics in compost to promote carbon sequestration and humic substance synthesis.

The incorporation of malonic acid (MA) into compost as a regulator of the tricarboxylic acid (TCA) cycle has the potential to increase carbon sequestration. However, the influence of MA on the transformation of the microbial community during the composting process remains unclear. In this investigation, MA was introduced at different stages of chicken manure (CM) composting to characterize the bacterial community within the compost using high-throughput sequencing. We assess the extent of increased carbon sequestration by comparing the concentration of total organic carbon (TOC). At the same time, this study examines whether increased carbon sequestration contributes to humus formation, which was elucidated by evaluating the content and composition of humus. Our results show that the addition of MA significantly improved carbon sequestration within the compost, reducing the carbon loss rate (C loss (%)) from 64.70% to 52.94%, while increasing HS content and stability. High throughput sequencing and Random Forest (RF) analysis show that the introduction of MA leads to a reduction in the diversity of the bacterial communities, but enhanced the ability of bacterial communities to synthesize humus. Furthermore, the addition of MA favors the proliferation of Firmicutes. Also, the hub of operational taxonomic units (OTUs) within the community co-occurrence network shifts from Proteobacteria to Firmicutes. Remarkably, our study finds a significant decrease in negative correlations between bacteria, potentially mitigating substrate consumption due to negative interactions such as competition. This phenomenon contributes to the improved retention of TOC in the compost. This research provides new insights into the mechanisms by which MA regulates bacterial communities in compost, and provides a valuable theoretical basis for the adoption of this innovative composting strategy.

Evolution from basic to advanced structure of fulvic acid and humic acid prepared by food waste.

Fulvic acid (FA) and humic acid (HA) are common polyacids in nature. However, the evolutionary process of their basic and advanced structures is still unclear. FA and HA were separated into five molecular weight components to investigate the process of evolution from small to large molecules. The primary structure analysis showed that FA were rich in CN, COOH and OH content, while HA were rich in (CH2)n, NH2 and CC. Moreover, with the molecular weight increasing, the structures could complement each other to maintain the hydrophilic or hydrophobic balance. The 2D-COS spectroscopy demonstrated that during the growth of FA, COOH, NH2 and OH firstly respond. On the other hand, during the growth of HA, NH2 and (CH2)n firstly respond. In addition, advanced structure of FA was affected by intramolecular hydrogen bonds and π - π interaction. HA was affected by hydrophobic interactions due to the abundance of hydrophobic groups, primarily (CH2)n and benzene rings. 3D conformational fitting and particle size characterization confirmed that the interaction forces determine that FA and HA become tightly and loosely molecules respectively. This study is to further explore the geochemical formation and evolution process of FA and HA molecules.

Insight into bacterial role attribution in dissolved organic matter humification during rice straw composting with microbial inoculation.

This study aims to investigate the effect of microbial role distribution in microbial carbon pumps on dissolved organic matter (DOM) humification during rice straw composting with microbial inoculation. Three composting groups were designed, named CK (control), B4 (with Bacillus subtilis, OR058594) and Z1 (with Aspergillus fumigatus, AF202956.1). As a result of inoculation, the composition of microbial communities was changed, so that the microorganisms that promoted DOM humification were concentrated in the responders in the microbial carbon pump. DOM was divided into three components in three composting treatments: C1, C2 and C3. After inoculation with Bacillus subtilis, the C2 component was significantly affected, while after inoculation with Aspergillus fumigatus, the C3 component was significantly affected. The results of physicochemical factors affecting the transformation of DOM fluorescence components indicated that C1, C2 and C3 were related to the abundance of the cellulose-degrading enzyme-encoding gene GH7 in CK and B4 composting. However, the C2 was susceptible to organic matter in Z1 composting. This study explored the distribution of microbial communities from a new perspective, which provided new information for analyzing DOM humification and treating agricultural straws to achieve clean conditions for environmental friendliness.

Effect of ferrous ions combined with zeolite on humification degree during food waste composting.

The research aims to clarify role of ferrous sulfate (FeSO4) combined with zeolite (Z) on humification degree based on investigation of concentration and structural stability of humic acid (HA) during food waste composting. Four treatments were set up, namely CK (control), Fe (5 %), Z (5 %) and Fe + Z (2.5 %+2.5 %). Results demonstrated that concentration and polymerization degree of HA were 53.4 % and 97.3 % higher in composting amended with Fe + Z than in the control, respectively. Meanwhile, formation of aromatic functional groups and recalcitrant fluorescent components (HAC3) was significantly promoted, indicating that Fe + Z treatment enhanced HA structure stability. The bacterial networks became tighter, and the proportion of core bacteria in dominant modules increased at Fe + Z treatment. Additionally, key factors affecting HAC3 and product quality were identified by structural equation models, which verified potential mechanism of humification enhancement. Overall, this study provided theoretical support for improving humification degree and product quality.

Improved carbon sequestration by utilization of ferrous ions during different organic wastes composting.

The humic acid (HA) possesses a more recalcitrant structure, making it crucial carbon components that improve carbon sequestration. Moreover, ferrous ions could improve microbial activity and enhance compost humification, and their oxidation into iron oxides could adsorb carbon components for sequestration. Based on the advantages of low cost and easy availability of ferrous sulfate (FeSO4), this study investigated the effect of FeSO4 on carbon sequestration during composting. Chicken manure (CM) and food waste (FW) composting were carried out in four treatments, namely control (CM, FW) and 5% (w/w) FeSO4 treated groups (CM+, FW+). Results indicated that FeSO4 increased HA content, improved organic carbon stability. Carbon loss for CM, CM+, FW and FW + treatments were 48.5%, 46.2%, 45.0%, and 40.3%, respectively. Meanwhile, FeSO4 enhanced the function of bacterial taxa involved in HA synthesis in CM + treatment, and improved the number of core bacteria significantly associated with formation of HA and iron oxide. SEM analysis verified that role of FeSO4 was significant in promoting HA synthesis during CM + composting, while it was remarkably in enhancing HA sequestration during FW + composting. This article provided fundamental theoretical backing for enhancing HA production and improving carbon sequestration during different materials composting.

Identify the potential driving mechanism of reconstructed bacterial community in reduce CO2 emissions and promote humus formation during cow manure composting.

The mineralization of organic components releases CO2 during composting, which not only leads to the loss of organic carbon, but has a direct negative impact on the environment. Malonic acid as a competitive inhibitor of succinate dehydrogenase could affect the tricarboxylic acid (TCA) cycle and reduce CO2 emissions. However, the bacterial interaction and organic component transformation has less known how to malonic acid reduce CO2 and improve of humus synthesis in complex composting. The aim of this study was to investigated the malonic acid on organic carbon sequestration and transforming cow manure waste into products with high humus content. Humus content was elevated by 16.8% and cumulative CO2 emissions (30 d)d reduced by 13.6% after malonic acid addition compared to the CK. SparCC analysis of bacterial interaction presented that the network complexity and stability was more higher with malonic acid addition, while a greater concentration of keystones and their ecological metabolic functions was observed, suggesting they weaken the influence of TCA cycle inhibition by enhancing interactions. PICRUSt predictions indicate that malonic acid might enhance humus content by promoting the synthesis of polyphenols and polymerization with amino acids. This study investigated the potential mechanism of regulators to enhance quality and reduce emissions during humification process, providing a new strategy for the resource utilization of organic solid waste.

Origin, distribution and spatial characteristics of dissolved organic matter in the Heilongjiang River.

The Heilongjiang River Basin is a vast area with significant DOM sources and composition differences. The mechanism of DOM degradation under spatial variation remains unclear. This research investigated the degradation characteristics of DOM in different watersheds of the Heilongjiang River. DOM levels were higher in midstream waters, while DOM degradation rates were higher in midstream and downstream waters. The parallel factor analysis (PARAFAC) results showed that the upstream amino acid fraction was significantly depleted, the midstream was dominated by the degradation of DOM of terrestrial origin, and the downstream humic acid fraction was decreased considerably. Gene sequencing results indicated that the upstream, middle, and downstream water bodies' microbial community composition and structure differed significantly. The network analysis results revealed microorganisms in upstream water bodies mainly utilized amino acid-like substances and small molecule humic acids. Microorganisms in the middle and lower reaches of the water column were characterized by the utilization of humic acid-like fractions. In this study, we further screened the key driving microorganisms (e.g., Flavobacterium and Lacibacter) responsible for the difference in the DOM utilization function of upstream-to-midstream and midstream-to-downstream microorganisms in the Heilongjiang River. These findings will help identify the cycling process of DOM under spatial variation and predict the succession pattern of microbial communities.

Insight into the pathways of biochar/smectite-induced humification during chicken manure composting.

As representative organic and inorganic additives, both biochar and smectite exhibit an excellent capacity to improve humification efficiency during composting. Nevertheless, the mechanisms underlying biochar/smectite-induced compost humification have still not been fully explored from the perspective of overall organic substances. In this study, three composting treatments were performed as follows: 10 % biochar-amended composting, 10 % smectite-amended composting and natural composting without any additive. UV-visible parameters and synchronous hetero two-dimensional correlation spectra showed that biochar accelerated dissolved organic matter (DOM) complications, unsaturation and aromatization. For example, biochar promoted the C2 and simple C3 peaks to convert into a sophisticated C3/360 peak. However, the effect of smectite was negligible in complicating the DOM structure. Both biochar and smectite displayed an invigorating role in promoting humic substance (HS) formation. The strengthened relations between bacterial richness and physicochemical indicators and HS fractions might contribute to the positive action of biochar/smectite on HS synthesis. Network analysis showed that both bacterial functional omnipotence and specialization in response to the addition of catalysts may contribute to compost humification. The chemical pathway involved in DOM humification was intensified by enhancing the role of pH in biochar composting and weakening the degradation of unsaturated aromatic compounds of DOM with smectite addition. These findings benefit the practical application of biochar/smectite in promoting composting efficiency.

Exploring the nitrogen fixing strategy of bacterial communities in nitrogen cycling by adding calcium superphosphate at various periods during composting.

Chicken manure, as an organic solid waste with a high nitrogen content, generates large amounts of ammonia during composting, which leads to pollution of the surrounding environment, and causes a reduction in the quality of the compost product. Nitrogen is transformed through the nitrogen cycle and bacterial communities are the main contributors to the transformation of the nitrogen cycle. The microbial composition changes dramatically at different stages during composting. Therefore, calcium superphosphate (SSP) was added to compost as a nitrogen-fixing agent to elucidate the strategy and function of the bacterial community involved in the nitrogen cycle. The results showed that the addition of SSP at the initial, high temperature and cooling stages increased the inorganic nitrogen (NH4+-N, NO3--N) content by 51.99 %, 202.72 % and 173.37 % compared to CK, respectively. In addition, nitrogen cycle functional genes (gdh, nifH, pmoA-amoA, hao, nxrA, nirK, napA, nosZ, narG) abundance were determined by real-time qPCR. The nitrogen cycle genetic results showed that SSP addition at high temperature phase resulted in a 62.43 % down-regulation of ammonification genes, while nitrogen fixation and nitrification genes were enhanced. Random forests revealed a shift in the participation strategy of bacterial communities (e.g., Mycobacterium, Izemoplasmatales, Paracoccus, Ruminococcus) within the nitrogen cycle, leading to altered importance rankings despite involvement in different nitrogen cycle pathways. Moreover, Regression analysis and structural equation modelling revealed that SSP addition at high temperature stage stimulated the bacterial community engaged in nitrogen fixation and nitrification, resulting in increased nitrogen accumulation as NO3--N during composting. This paper offers the potential to yield novel scientific insights into the impact of microbially mediated nitrogen transformation processes and reduce gaseous pollution.

Identifying the specific pathways to improve nitrogen fixation of different straw biochar during chicken manure composting based on its impact on the microbial community.

The application of straw biochar to chicken manure composting mitigated nitrogen loss. However, the impact of biochar derived from different types of straw on nitrogen fixation in chicken manure composting is discrepant, and the specific pathways remain unclear. Therefore, this study aimed to clarify the specific pathways of maize straw biochar (M) and rice straw biochar (R) to improve nitrogen fixation during chicken manure composting. The nitrogen losses in control (no addition, CK), M, and R composting were 51.84 %, 33.47 %, and 38.24 %, respectively, suggesting that adding straw biochar effectively improved nitrogen fixation. Microbial community analysis suggested that inhibiting denitrification and NH4+-N transformation by microorganisms was the primary means of improving nitrogen fixation. Meanwhile, biochar addition reduced the number of bacteria participating in nitrogen transformation and strengthened the NO3--N and total organic nitrogen transformation processes, among which the effect of M composting was stronger. The stronger effect was attributed to the significant role of the core microorganisms in M composting in shifting the transformation processes of the nitrogen components (P < 0.05). Therefore, the function of different straw biochar was determined by its different impacts on the microbial community, highlighting the important role of microbial community variability.

The contribution of microbial shikimic acid to humus formation during organic wastes composting: a review.

Microbial shikimic acid is an important intermediate metabolite in the synthesis of aromatic amino acids which are precursors for forming humus during composting process. Generally, the pathways producing shikimic acid and its downstream products are collectively referred as shikimic acid pathway (SKP). Microbial SKP can produce phenols, and tyrosine. Pyrogallol is the precursor of phenols. And, tyrosine can form an ammoniated monomer. Therefore, regulation of SKP can promote shikimic acid production, which is beneficial in promoting humus production and humification. However, SKP present in microbial cells is distinctive because of providing precursors for humification process, which needs to be recognized during composting. Due to the different structures of various organic wastes, it is difficult to control the SKP efficiency and shikimic acid production. Therefore, it is valuable to review the synthesis of shikimic acid by microorganisms and propose how to promote SKP during different materials composting. Furthermore, we have attempted to illustrate the application of metabolites from SKP in forming humus during organic waste composting. Finally, a series of regulating methods has been outlined to enhance microbial SKP, which are effective to promote humus aromatization and to improve humus formation during different materials composting.

Effect of microbial pretreatment on degradation of food waste and humus structure.

The study aimed to investigate the pretreatment characteristics of food waste (FW) by Bacillus licheniformis and Bacillus oryzaecorticis, and to determine the contribution of microbial hydrolysis in the structure of fulvic acid (FA) and humic acid (HA). FW was pretreated with Bacillus oryzaecorticis (FO) and Bacillus licheniformis (FL), and the resulting solution was heated to synthesize humus. The results showed that the acidic substances produced by microbial treatments led to a decrease in pH. In addition, Bacillus oryzaecorticis degraded starch and released a large amount of reducing sugar, providing OH and COOH to FA molecules. Bacillus licheniformis showed a positive effect on the HA structure, which had higher OH, CH3 and aliphatics. FO is more beneficial to retain OH and COOH, while FL is more beneficial to retain amino and aliphatics. This study provided evidence for the application of Bacillus licheniformis and Bacillus oryzaecorticis in waste management.

Fate of dissolved organic matter affected by oxytetracycline tolerant microorganisms during chicken manure composting.

This study explored the interaction among the components of dissolved organic matter (DOM), environmental factors and oxytetracycline (OTC) tolerant bacteria during chicken manure composting using Parallel Factor Analysis (PARAFAC) and 16S rRNA sequencing analysis. The results revealed that the OTC residues in chicken manure may affect the transformation between the protein-like component (C1) and humus-like component (C2 and C3) during composting. The transformation of DOM components under the OTC stress was indirect by affecting the microbial community activity. The OTC tolerant bacteria that still exist after the high temperature period of composting had a significant positive correlation between the humification process. The correlations of the dissolved organic carbon (DOC), total nitrogen (TN), and core OTC tolerant bacteria with DOM components, which enhanced the cooperative function of DOM component transformation. To clarify the influence of OTC residue on the humification process can promote the composting carbon fixation and improve composting quality.