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.

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.

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.

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.

Microbial inoculants reshape structural distribution of complex components of humic acid based on spectroscopy during straw waste composting.

This study aimed to explore the mechanism of actinomycetes inoculation to promote humification based on spectroscopy during straw waste composting. Results showed that inoculating actinomycetes could significantly increase the humification index and humification ratio, which were 2.53% and 21.79% respectively (P < 0.05). A spectroscopic analysis suggested that actinomycetes promoted the relative content of complex components of humic acid and reshaped the structural distribution of two sub fluorescence peaks in it. Furthermore, variance partitioning analysis demonstrated that compared with the intensity, the high-quality uniform distribution of fluorescence peaks had a greater contribution to the improvement of humification. In addition, structural equation model further verified that actinomycetes inoculation promoted the transformation of fulvic acid to humic acid, and then promoted the formation of humic acid. Therefore, actinomycetes inoculation can promote the humification of straw compost by reshaping the complex components of humic acid.

Resource utilization of mink manure: Functional microbial inoculation to elevate the bioavailability of organic nitrogen during composting.

Mink manure is one of the high nitrogenous wastes, which can easily cause nitrogen mineralization during composting, resulting in low resource reutilization. However, there are few studies on the resource utilization of mink manure. Therefore, this study investigated the effects of functional microbial (bacterial and actinomycetes agents) inoculation on nitrogen mineralization during mink manure composting. Results suggested that the inoculum, especially actinomycetes agents, could increase organic nitrogen and bioavailable organic nitrogen (BON) content. Principal component analysis and Random Forest model demonstrated that the inoculants increase the abundance of microorganisms that positively correlated with BON, decrease the microorganisms that negatively correlated with BON. Consequently, the inoculation of functional microbial agents could effectively reduce nitrogen mineralization and improve composting quality. Therefore, this study provided theoretical and technical support for optimizing mink manure composting, promoting the resource utilization of high nitrogen wastes.

Identifying the role of fired clay minerals on reducing of nitrogen loss and immobilization of organic nitrogen during chicken manure composting.

This study compared effects of clay minerals before and after firing in immobilization of organic nitrogen and reducing of nitrogen loss during chicken manure composting. The clay minerals and fired clay minerals treatments increased organic nitrogen contents and significantly reduced nitrogen loss, the loss was in order CK (52.61%) > M (47.15%) > I (45.90%) > M- (42.58%) > I- (40.59%). Meanwhile, network analysis indicated that core bacterial community associated with nitrogen transformation were more abundant, and conversion effect of single core bacteria on nitrogen components was enhanced in fired clay minerals treatments. In addition, fired clay minerals strengthened correlation between environmental factors, bacterial community and organic nitrogen, and enhanced interaction of abiotic and biotic pathways, which verified by variance partitioning analysis and structural equation model. Therefore, fired clay minerals play a remarkable driving role in formation and immobilization of organic nitrogen.

The remarkable role of shikimic acid pathway in humic acid formation during biochar and montmorillonite addition composting.

The final products of shikimic acid pathway, aromatic amino acids (AAA), can be used as humic acid (HA) precursors. Therefore, the aim of this study was to explore the contribution of shikimic acid pathway on the formation of HA during composting. Four composting treatments were carried out in this study, including the control, biochar addition, montmorillonite addition, biochar and montmorillonite combined addition. The results showed that the correlations between AAA and HA were enhanced during combined addition composting, and functional microorganisms involved in the shikimic acid pathway increased. In addition, random forest model suggested that 63.3% of the top 30 genera contributing to the HA formation were functional microorganisms involved in the shikimic acid pathway, which fully proved the critical role of shikimic acid pathway. Therefore, this study provided a new perspective for revealing the crucial factors that promoted the formation of HA during composting.

Modified montmorillonite and illite adjusted the preference of biotic and abiotic pathways of humus formation during chicken manure composting.

The study aimed to identify the preference of pathways of humus formation. Five lab-scale composting experiments were established: the control (CK), montmorillonite addition (M), illite addition (I), thermal treatment montmorillonite addition (M-) and thermal treatment illite addition (I-). Results showed humus content was increased by 11.5%, 39.3%, 37.2%, 30.9% and 27.6% during CK, M-, M, I- and I composting. Meanwhile, Redundancy analysis indicated the bands of bacteria community related to humic acid (HA) were more abundant in the M- and I- treatments. Furthermore, structural equation model and variance partitioning analysis demonstrated that M- and I- treatments promoted precursors to synthesize HA by coordinated regulation of biotic pathway and abiotic pathway, the increase of HA in the M and I treatments mainly through the abiotic pathway. In summary, an effective method was proposed to improve humus production by adjusting the preference of biotic and abiotic pathways of humus formation.

Effect of tricarboxylic acid cycle regulators on the formation of humic substance during composting: The performance in labile and refractory materials.

The aims of this study are to reveal the roles of tricarboxylic acid (TCA) cycle regulators in reducing CO2 emission and promoting humic substance (HS) formation during composting with different materials. The results showed that the addition of adenosine tri-phosphate (ATP) or malonic acid (MA) reduced CO2 emission during chicken manure composting. However, only the addition of MA reduced CO2 emission during lawn waste and garden waste composting. In addition, both of the two inhibitors promoted HS formation, especially for ATP. Structural equation models further confirmed that ATP and MA reduced CO2 emission by inhibiting the decomposition of amino acid by microorganisms. Meanwhile, ATP promoted the conversion of amino acid and soluble sugars to HS, while MA only promoted the conversion of soluble sugars to HS. In summary, this study provides a theoretical basis for the application of inhibitors to reduce CO2 emission and promote HS formation during composting.

Assessment of Multiorigin Humin Components Evolution and Influencing Factors During Composting.

Humin (HM) is a complex mixture of molecules produced in the different biological processes, and the structural evolution of HM in the agricultural wastes composting are not well-known. Elucidating and comparing the structural evolution during livestock manure (LMC) and straw wastes (SWC) composting can help one to better understand the fates, features, and environmental impacts of HM. This study exploits excitation emission matrix-parallel factor (EEM-PARAFAC), two-dimensional correlation spectroscopy (2D-CoS), hetero-2DCoS, and structural equation model (SEM) to compare the fate of the HM. We fit a three-component EEM-PARAFAC model to characterize HM extracted from LMC and SWC. The results show that the HM evolution has a significant difference between LMC and SWC. As a result, the opposite change tendency and different change order of HM fluorescent components determine the different synthesis formation and evolution mechanisms. The diverse organic matter composition and dominant microbes might be the reason for the different evolution mechanism. Based on these results, a comprehensive view of the component changes of HM in the composting process is obtained. Furthermore, the superior potential of such an integrated approach during investigating the complex evolution in the environment was also demonstrated.