The effect of calcium superphosphate addition in different stages on the nitrogen fixation and ammonification during chicken manure composting

Effects of nitrification inhibitors DCD and DMPP on maturity, N2O and NH3 emissions during manure composting

In order to reduce N2O emissions during composting, the effects of different nitrification inhibitors (NI), dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP), on compost maturity, N2O, and NH3 emissions were studied under continuous incremental addition. This study used pig manure and corn straw as composting materials, based on the total nitrogen (TN) content of the initial mixture, two treatments were set: DCD (2.5% in the early phase and 5.0% in the maturation phase) and DMPP (0.25% in the early phase and 0.75% in the maturation phase) in a composting experiment. The results showed that adding DCD and DMPP did not affect the compost maturity, with the seed germination index (GI) of final compost reaching 80.76%-97.06%. Before the maturity period of compost, ammonia (NH3) emissions accounted for 98.5%-99.4% of total emissions. Compared with the control group (CK), the addition of DCD and DMPP in the early stage reduced NH3 emissions by 8.85% and 12.83%, respectively, by decreasing the ammonification rate. During the mature stage of composting, N2O emissions account for 95.6%-98.9% of the total emissions. The addition of DCD and DMPP delayed N2O emissions by 4 and 6 days, respectively, through nitrification inhibition. The DMPP amendment also reduced cumulative N2O emissions by 54.50% and increased the nitrogen content of the final compost. Correlation analysis showed that N2O was mainly originated from the denitrification of nitrification substrate (NO2--N and NO3--N). This study provides technical support for low-carbon management of agricultural waste.

Confirming the key factors influencing the biosynthesis and regulation of organic nitrogen in composting

Organic nitrogen (ON) possesses the ability to sustain a stable nitrogen supply fertility during composting. However, research on the biosynthesis and regulation of ON remains limited. The results indicated that despite variations in microbial communities between the chicken manure composting (T group) and kitchen waste digestate composting (F group), their functional genes were remarkably similar, and the microorganisms exhibited similar functions. The microbial community structure of T group was more complex than that of F group. Network analysis identified Saccharomonospora, Corynebacterium, and Thermobifida as the core microorganisms in T group, whereas Oceanobacillus, Staphylococcus, and Fictibacillus were predominant in F group. These microorganisms play a role in the biosynthesis and regulation of various forms of ON (including amino acid nitrogen (AAN), amino sugar nitrogen (ASN), amide nitrogen (AN) and hydrolyzable unknown nitrogen (HUN)) and may contribute to differences in ON production due to the distinct nature of the materials. The core functional genes of the two groups of materials were determined by random forest model. Although differences in functional genes were present between F group and T group, the most crucial genes for ON biosynthesis in both groups were those with ammonia assimilation (such as glnE, gltB, gltD, etc.). The nitrogen transformation processes associated with these core genes can be modulated by managing the activity of multifunctional microorganisms, particularly through the control of ammonia assimilation, nitrate reduction, and ammonification, which are related to NH4+ levels. Notably, electric conductivity (EC), temperature (Tem.), pH, and NH4+ were the pivotal environmental factors influencing the biosynthesis of ON. This investigation enhances our understanding of the previously underexplored mechanisms of ON biosynthesis and regulation.

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.

Effect of nitrogen retention composite additives Ca(H2PO4)2 and MgSO4 on the degradation of lignocellulose, compost maturation, and fungal communities in compost

This study investigated the effects of the nitrogen retention composite additives Ca(H2PO4)2 and MgSO4 on lignocellulose degradation, maturation, and fungal communities in composts. The study included control (C, without Ca(H2PO4)2 and MgSO4), 1% Ca(H2PO4)2 + 2% MgSO4 (CaPM1), 1.5% Ca(H2PO4)2 + 3% MgSO4 (CaPM2). The results showed that Ca(H2PO4)2 and MgSO4 enhanced the degradation of total organic carbon (TOC) and promoted the degradation of lignocellulose in compost, with CaPM2 showing the highest TOC and lignocellulose degradation. Changes in the three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) of dissolved organic matter (DOM) components in compost indicated that the treatment group with the addition of Ca(H2PO4)2 and MgSO4 promoted the production of humic acids (HAs) and increased the degree of compost decomposition, with CaPM2 demonstrating the highest degree of decomposition. The addition of Ca(H2PO4)2 and MgSO4 modified the composition of the fungal community. Ca(H2PO4)2 and MgSO4 increased the relative abundance of Ascomycota, decreased unclassified_Fungi, and Glomeromycota, and activated the fungal genera Thermomyces and Aspergillus, which can degrade lignin and cellulose during the thermophilic stage of composting. Ca(H2PO4)2 and MgSO4 also increased the abundance of Saprotroph, particularly undefined Saprotroph. In conclusion, the addition of Ca(H2PO4)2 and MgSO4 in composting activated fungal communities involved in lignocellulose degradation, promoted the degradation of lignocellulose, and enhanced the maturation degree of compost.

Effects of Bacillus-based inoculum on odor emissions co-regulation, nutrient element transformations and microbial community tropological structures during chicken manure and sawdust composting

This study aims to evaluate whether different doses of Bacillus-based inoculum inoculated in chicken manure and sawdust composting will provide distinct effects on the co-regulation of ammonia (NH3) and hydrogen sulfide (H2S), nutrient conversions and microbial topological structures. Results indicate that the Bacillus-based inoculum inhibits NH3 emissions mainly by regulating bacterial communities, while promotes H2S emissions by regulating both bacterial and fungal communities. The inoculum only has a little effect on total organic carbon (TOC) and inhibits total sulfur (TS) and total phosphorus (TP) accumulations. Low dose inoculation inhibits total potassium (TK) accumulation, while high dose inoculation promotes TK accumulation and the opposite is true for total nitrogen (TN). The inoculation slightly affects the bacterial compositions, significantly alters the fungal compositions and increases the microbial cooperation, thus influencing the compost substances transformations. The microbial communities promote ammonium nitrogen (NH4+-N), TN, available phosphorus (AP), total potassium (TK) and TS, but inhibit nitrate nitrogen (NO3--N), TP and TK. Additionally, the bacterial communities promote, while the fungal communities inhibit the nitrite nitrogen (NO2--N) production. The core bacterial and fungal genera regulate NH3 and H2S emissions through the secretions of metabolic enzymes and the promoting or inhibiting effects on NH3 and H2S emissions are always opposite. Hence, Bacillus-based inoculum cannot regulate the NH3 and H2S emissions simultaneously.

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.

Effects of adding corn steep liquor on bacterial community composition and carbon and nitrogen transformation during spent mushroom substrate composting

BACKGROUND

Carbon and nitrogen are essential energy and nutrient substances in the composting process. Corn steep liquor (CSL) is rich in soluble carbon and nitrogen nutrients and active substances and is widely used in the biological industry. Nonetheless, limited research has been done on the effect of CSL on composting. This work firstly reveals the effect of adding CSL to bacterial community composition and carbon and nitrogen conversion during composting. This study provides the choice of auxiliary materials for the spent mushroom substrate compost (SMS) and some novel knowledge about the effect of bacterial community on C and N cycling during composting of SMS and CSL. Two treatments were set up in the experiment: 100% spent mushroom substrate (SMS) as CK and SMS + 0.5% CSL (v/v) as CP.

RESULTS

The results showed that the addition of CSL enhanced the initial carbon and nitrogen content of the compost, altered the bacterial community structure, and increased the bacterial diversity and relative abundance, which might be beneficial to the conversion and retention of carbon and nitrogen in the composting process. In this paper, network analysis was used to screen the core bacteria involved in carbon and nitrogen conversion. In the CP network, the core bacteria were divided into two categories, synthesizing and degrading bacteria, and there were more synthesizing bacteria than degrading bacteria, so the degradation and synthesis of organic matter were carried out simultaneously, while only degrading bacteria were found in the CK network. Functional prediction by Faprotax identified 53 groups of functional bacteria, among which 20 (76.68% abundance) and 14 (13.15% abundance) groups of functional bacteria were related to carbon and nitrogen conversion, respectively. Adding CSL stimulated the compensatory effect of core and functional bacteria, enhanced the carbon and nitrogen transformation ability, stimulated the activity of low-abundance bacteria, and reduced the competitive relationship between the bacterial groups. This may be why the addition of CSL accelerated the organic matter degradation and increased carbon and nitrogen preservation.

CONCLUSIONS

These findings indicate that the addition of CSL promoted the cycling and preservation of carbon and nitrogen in the SMS composts, and the addition of CSL to the compost may be an effective way to dispose of agricultural waste.