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

Effect of chicken manure and superphosphate on accelerating green waste composting and enhancing nutrient retention

Efficient green waste (GW) management through composting is essential for promoting cleaner production and fostering a green economy. However, traditional GW composting often faces challenges such as extended decomposition times, significant nitrogen losses, and low nutrient content in the final compost product. This research evaluated the effects of incorporating chicken manure (CM: 0, 15, and 30%) and superphosphate (SSP: 0, 5, and 10%) on GW composting. A control treatment without additives was included for comparison. Results demonstrated that the combination of 15% CM and 5% SSP significantly enhanced the composting process, achieving maturity and stability within just 33 days-6 days faster than the control. This treatment also extended the thermophilic phase by 8 days, increased electrical conductivity by 115%, improved organic matter decomposition by 49%, and elevated the germination index by 56%. Furthermore, the final compost showed higher nutrient levels, with total nitrogen, total phosphorus, and total potassium content exceeding the control by 92%、327%、135%, respectively. These findings highlight the synergistic effects of CM and SSP in accelerating GW composting and enhancing compost quality, offering valuable insights for the sustainable and resource-efficient management of GW.

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.

Enhancing compost quality: Biochar and zeolite's role in nitrogen transformation and retention

This research evaluated how addition of biochar and zeolite affected nitrogen transformation and retention during the composting of kitchen waste. Four treatments, control (CK), 10 % biochar (B), 10 % zeolite (Z), and 5 % biochar +5 % zeolite (BZ) were used to study nitrogen transformation and retention. The results showed that biochar and zeolite can significantly reduce the loss of NH4+-N during the thermophilic phase (CK: 42.6 %, B: 35.1 %, Z: 35.7 %, and BZ: 31.3 %). Network analysis showed that biochar and zeolite increased the number of microorganisms associated with nitrification genes while decreasing the number of microorganisms associated with denitrification genes, preventing nitrogen volatilization in N2O. Mantel tests further demonstrated that biochar and zeolite enhanced the correlation between bacterial communities and the relationship between NH4+-N, NO3--N, and organic nitrogen was weakened, thus inhibiting the mineralization of organic nitrogen. Therefore, biochar and zeolite played an active role in promoting the transformation and retention of nitrogen components. Biochar and zeolite for kitchen waste also provided a new perspective on the treatment of kitchen waste.

Impact of cellulolytic nitrogen-fixing composite inoculants on humification pathways and nitrogen cycling in kitchen waste composting

Low humification and nitrogen loss pose substantial challenges to the resource utilization in kitchen waste composting. This study investigated the effects of brown-rot fungi (BRF), cellulolytic nitrogen fixing bacteria (CNFB), and their composite microbial inoculants (CMI) during composting. Results indicated that microbial inoculants extended the thermophilic phase and enhanced cellulose degradation. Compared with the control, the degree of polymerization (HA/FA) in BRF, CNFB, and CMI was 2.28, 1.85, and 2.68 times higher, respectively, while increasing total nitrogen by 11.15%, 15.50%, and 19.73%. BRF and CMI primarily enhanced the Maillard humification pathway, while CNFB promoted the polyphenol humification pathway. Additionally, BRF enhanced nitrification and reduced denitrification, whereas CNFB and CMI improved nitrification, nitrogen fixation, and ammonification while reducing denitrification. Overall, BRF primarily promoted humification, while CNFB excelled in nitrogen retention. The CMI achieved optimal humification and nitrogen retention, indicating a potential sustainable solution for kitchen waste composting.

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.