Effects of adding lignocellulose-degrading microbial agents and biochar on nitrogen metabolism and microbial community succession during pig manure composting

Improvement in lignocellulose degradation and humus synthesis by adding gallic acid during cow manure composting

The positive effects of adding polyphenols on humification have been widely explored during composting. However, the precise impact of polyphenols on the breakdown of lignocellulose throughout the composting process has not yet been elucidated. Two experimental treatments were designed to explore the mechanism by which adding natural organic phenols affected interactive relationship between lignocellulose hydrolysis and humus synthesis: a control group and a gallic acid (GA)-amended group. The results indicated that GA effectively promoted the transformation of polyphenols. Degradation rates of lignin and cellulose increased by 42.3 % and 20.6 %, respectively. Meanwhile, the synthesis of highly humified component 3 of humic acid increased by 22.1 % in GA group. GA dramatically enriched core bacteria associated with humic acid components. Structural equation model showed that GA directly stimulated microbial decomposition of lignocellulose and indirectly accelerated its degradation by enhancing microbial utilization of polyphenols. These enhancements in polyphenol transformation and lignin degradation collectively promoted compost humification. The addition of GA presents a highly promising approach to accelerate the degradation of recalcitrant lignocellulose and promote compost humification, while simultaneously addressing the waste generated during the production process of polyphenols.

Unveiling the nitrogen metabolism mechanism for nitrogen retention in compost via in-situ ammonia recycling strategy

A large amount of ammonia volatilization in compost causes environmental pollution and reduces the quality of compost. Ammonia recycling composting strategy (ARCS) is new strategy for reducing ammonia volatilization by absorbing with backfilling ammonia into the compost. This study revealed the mechanism of ARCS on ammonia volatilization and nitrogen retention during chicken manure composting. The results showed that the adsorption layer containing wood vinegar had an obvious inhibition effect on ammonia volatilization. Compared to CK, ARCS treatment could reduce ammonia emissions and nitrogen loss by 20.65% and 39.6% with T3 (12d), respectively. Different adsorption time would affect the occurrence of various nitrogen components in the adsorption layer, especially the change of inorganic nitrogen content. Metagenomic analysis showed that ARCS treatment resulted in significant changes in bacterial communities, and different backfilling times had significant effects on nitrogen metabolism pathways in compost. Glutamate dehydrogenase and glutamate synthase were the key nitrogen metabolism processes during composting, which played an important role in ammonia volatilization and nitrogen retention. The suitable backfilling time (12d) promoted the acceleration of ammonia nitrogen metabolism in the early stage of composting and enhanced the ammonia assimilation and dissimilatory nitrate reduction function in the maturation stage to achieve nitrogen retention. This study provided valuable insights into the effects of in-situ ammonia absorption and backfilling on nitrogen metabolism pathways during composting.

Predicting the adsorption of ammonia nitrogen by biochar in water bodies using machine learning strategies: Model optimization and analysis of key characteristic variables

Biochar adsorption technology has been widely used to remove ammonia nitrogen from water bodies. However, existing methods for predicting adsorption efficiency often lack sufficient accuracy and practical usability. This study evaluated eight machine learning models, including XGB, LR, KNN, DT, RF, GBR, SVR, and ANN, to predict the adsorption efficiency of ammonia nitrogen. The evaluation utilized a dataset comprising 770 instances of ammonia nitrogen adsorption by biochar. The models' prediction performances were systematically compared, and cross-validation was applied to enhance their generalization ability, leading to the selection of the best-performing model. The selected model's parameters were further optimized using Bayesian optimization to improve the prediction accuracy. The Bayesian-optimized XGB model achieved the highest predictive performance, with a coefficient of determination (R2) of 0.978. The R2 values of the other models ranged from 0.556 (LR) to 0.927 (RF). Key factors influencing ammonia nitrogen adsorption efficiency were identified using SHAP analysis. These factors included biochar dosage, adsorption time, initial ammonia nitrogen concentration, solution pH, pyrolysis time, and O%. Their optimal ranges were further determined through partial dependency plots. This study developed a reliable machine learning tool for accurately predicting ammonia nitrogen adsorption efficiency. Additionally, it provided insights into optimizing the preparation processes and adsorption conditions of biochar, contributing to its practical application in treating ammonia nitrogen pollution in water bodies.

Effects of biochar-loaded microbial agent in regulating nitrogen transformation and integration into humification for straw composting

Exogenous additives can impact organic matter transformation in composting, but their effects on nitrogen conversion and humification in straw composting require clarification. This study investigated how rice husk biochar-loaded microbial agent (RM) affects nitrogen transformation and humification during straw composting. Results showed that the addition of RM enhanced ammonia oxidation and assimilation during composting, leading to a 10.32%-22.27% increase in total nitrogen content. Furthermore, the RM treatment enriched nitrogen-converting microbes such as Longispora and Coprinopsis, enhancing synergistic relationships among microbes, facilitating the accumulation of pivotal nitrogenous humus precursors (amino acid nitrogen), and promoting humus formation. This research not only guides reducing nitrogen loss during composting and elucidating the relationship between nitrogen transformation and humification but also contributes to enhancing bioconversion efficiency of agricultural waste to explore new ways of straw waste management.

Feedstock optimization with low carbon to nitrogen ratio during algal sludge aerobic composting: Quality and gaseous emissions

This study investigated compost quality and gaseous emissions during the algal sludge composting. The experiment explored the feasibility of low initial carbon to nitrogen (C/N) ratio composting by using different volume ratios of algal sludge and spent mushroom substrates (1:1, 1:2, 1:3, and 1:4, corresponding to C/N ratios of 9.5, 12.3, 14.6, 16.0, respectively). The results showed that increasing the proportion of algal sludge in the initial material led to a longer maturation time and higher nitrogen losses but also enhanced the mineralization of organic nitrogen (converted to NH4+ and NO3-) and reduced carbon losses. The addition of carbon-rich bulking agents within a certain range improved the diversity and interactions of bacterial communities during algal sludge composting. In conclusion, considering the nitrogen and carbon lost, retained, and made available across the four treatments, treatment 3 (C/N = 14.6) appears to be the optimal choice for low C/N composting.

Efficiency and mechanisms for enhancing nitrogen retention in distilled grain waste compost through a composting-biofiltration approach

Composting is an effective method for recycling resources in waste management. However, significant nitrogen loss can hinder the overall effectiveness of the composting process. Biofiltration is a promising method for conserving nitrogen in composting owing to its ability to efficiently trap and convert gaseous emissions. This study investigated the efficiency and mechanisms of a composting-biofiltration system to enhance nitrogen retention in distilled grain waste (DGW) compost using pre-composted DGW as biofilter media. The DGW composting-biofiltration system exhibited a lower nitrogen loss (24.9%) than the mono-composting system (40.1%). Additionally, this DGW system achieved a high NH3 removal efficiency of 94.7%-97.7%, while NO3- concentration continuously increased in the biofilter, indicating that biofiltration mainly conserved nitrogen through the conversion of NH3 emitted from the composter. The analysis of the microbial community and key functional enzymes involved in nitrogen metabolism revealed a significant increase in both nitrification and ammonia assimilation within the biofilter. This resulted in the accumulation of NO3- and the formation of organic nitrogen, thereby facilitating nitrogen retention. Genera such as Chryseolinea, Anseongella, Parapusillimonas, Bacillus, and Urebacillus mainly contributed to the generation of NO3- and organic nitrogen. The structural equation model analysis revealed that nitrogen retention in DGW compost was mainly facilitated by enhanced nitrification and ammonia assimilation in the biofilter. These results provide insights into underlying mechanisms for enhancing nitrogen retention through a composting-biofiltration approach and present guidance for improving compost quality.

The activation of Parageobacillus toebii in hyperthermophilic composting was depended on the bioavailability of raw materials

Hyperthermophilic composting (HTC) with excellent disposal effect is a novel composting technology by inoculating exogenous thermophilic microorganisms. However, the role of exogenous thermophilic microorganisms in HTC remains debated, especially for the applicability of different compost feedstocks. In this study, the role of Parageobacillus toebii during HTC using chicken and pig manure was investigated. The addition of P. toebii could raise the maximum temperature to 78.2 °C and obviously enhanced maturation effect in chicken manure composting. However, the enhancement effect of P. toebii was weaker in pig manure compost, and the maximum temperature only reached 73 °C. Addition of P. toebii could stimulated functional microbial communities for C&N transformation, increased temperature, and promoted the growth of thermophilic microorganisms in chicken manure composting. Component analyses showed that chicken manure had higher bioavailability compared to pig manure. Correlation analysis indicated that P. toebii activated as a "leader", stimulating metabolic activity among functional microbial communities and enhancing organic matter degradation for heat release, while its activation depended on the bioavailability of the raw material. This study provides important insights into the role and application of exogenous microorganisms in promoting HTC.

Promoting role of nitrogen-fixing bacteria and biochar on nitrogen retention and degradation of PBAT plastics during composting

Since the increasing number of polybutylene adipate terephthalate (PBAT)-based plastics entering the environment, the search for sustainable treatment methods has become a primary focus of contemporary research. Composting offers a novel approach for managing biodegradable plastics. However, a significant challenge in the composting process is how to control nitrogen loss and enhance plastic degradation. In this context, the effect of various additives on nitrogen retention, PBAT plastics degradation, and microbial community dynamics during composting was investigated. The findings revealed that the addition of nitrogen-fixing bacteria Azotobacter vinelandii and biochar (AzBC) significantly improved nitrogen retention and accelerated PBAT rupture within 40 days of composting. Specifically, the PBAT degradation rate in the AzBC group reached 29.6%, which increased by 12.14% (P < 0.05) compared to the control group. In addition, the total nitrogen (TN) content increased by 6.20% (P < 0.05), and the Nitrogen-fixing enzyme (NIT) content increased by 190 IU/L (P < 0.05). Further analysis of GC-MS confirmed the presence of low molecular weight fragmentation products, such as 6-(4-hydroxybutoxy)-6-oxohexanoic acid. The AzBC treatment promoted the proliferation of Klebsiella at the genus level that could enhance nitrogen retention and the bacteria that have the ability to degrade PBAT, such as Proteobacteria and Firmicutes at the phyla level, and Pseudoxanthomonas, Pseudomonas, and Flavobacterium genera at the genera level (P < 0.05). Correlation analysis indicated that the degradation of PBAT is positively correlated with Temperature (T), NIT, and TN, but negatively correlated with the organic matter (OM) content and germination index (GI). In conclusion, the co-application of biochar and Azotobacter vinelandii offers promising sustainable prospects for enhancing PBAT plastic degradation and reducing nitrogen loss during composting.

Ecological practices increase soil fertility and microbial diversity under intensive farming

Intensive farming offers a potential solution to feed the growing population due to its high productivity. Conventional management (CO) based on inorganic fertilization practices degrades soil quality, but restorative practices including ecological intensification (EI) and organic management results in maintaining soil quality without compromising productivity. In this paper, two different management systems were evaluated: CO, based on inorganic fertilization, and EI, focused on providing organic nutrients to soils to support crops. EI increased soil fertility, together with higher alpha diversity indices, more differentially abundant amplicon sequence variant (ASVs) (247 EI vs. 165 CO) and indicator taxa (60 EI vs. 32 CO). Distinct bacterial taxa were associated with the different management systems, revealing their roles in soil processes and nutrient availability. In the CO treatment, indicator genera such as Nitrospira and Desulfarculaceae were linked to N fertilization and nitrite oxidation, while RB41 was associated with phosphorus availability. Ammoniphilus, PAUC26f, and BSV26 were also indicators of CO management. Conversely, EI treatment promoted bacteria involved in organic matter decomposition and nutrient cycling, such as Halomonas, Chryseolinea and Rhodobacteraceae. Gemmatimonas, Steroidobacter, Altererythrobacter, Acidibacter and Anseongella contribute to carbon and nitrogen cycling. Burkholderiaceae and Rhodopirellula play roles in phosphate solubilization and organic P mineralization, respectively. Numerous taxa with plant growth-promoting (PGP) attributes, such as BIrii41, Pseudomonas, and Lysobacter, were also identified as indicators of the EI treatment. EI associated bacteria were positively correlated with soil organic carbon contents, nitrates, and exchangeable bases, while negatively correlated with CO bacteria. A distance-based multivariate multiple regression (DistLM) demonstrated a strong relationship (r2 = 0.78) between soil physicochemical variables and bacterial community structure, with SOC explaining the most variations in the model. Other significant parameters included potassium (K), electrical conductivity (EC), and nitrates. The results suggest that EI promotes more sustainable soils in terms of fertility and microbial diversity.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

Urease-producing bacteria combined with pig manure biochar immobilize Cd and inhibit the absorption of Cd in lettuce (Lactuca sativa L.)

The synergistic remediation of heavy metal-contaminated soil by functional strains and biochar has been widely studied. However, the mechanisms by which urease-producing bacteria combine with pig manure biochar (PMB) to immobilize Cd and inhibit Cd absorption in vegetables are still unclear. In our study, the effects and mechanisms of PMB combined with the urease-producing bacterium TJ6 (TJ6 + PMB) on Cd adsorption were explored. The effects of TJ6 + PMB on the Cd content and pH of the leachate were also studied through a 56-day soil leaching experiment. Moreover, the effects of the complexes on Cd absorption and microbial mechanisms in lettuce were explored through pot experiments. The results showed that PMB provided strain TJ6 with a greater ability to adsorb Cd, inducing the generation of CdS and CdCO3, and thereby reducing the Cd content (71.1%) and increasing the pH and urease activity in the culture medium. TJ6 + PMB improved lettuce dry weight and reduced Cd absorption. These positive effects were likely due to (1) TJ6 + PMB increased the organic matter and NH4+ contents, (2) TJ6 + PMB transformed available Cd into residual Cd and decreased the Cd content in the leachate, and (3) TJ6 + PMB altered the structure of the rhizosphere bacterial and fungal communities in lettuce, increasing the relative abundances of Stachybotrys, Agrocybe, Gaiellales, and Gemmatimonas. These genera can promote plant growth, decompose organic matter, and release phosphorus. Interestingly, the fungal communities were more sensitive to the addition of TJ6 and PMB, which play important roles in the decomposition of organic matter and immobilization of Cd. In conclusion, this study revealed the mechanism by which urease-producing bacteria combined with pig manure biochar immobilize Cd and provided a theoretical basis for safe pig manure return to Cd-polluted farmland. This study also provides technical approaches and bacterial resources for the remediation of heavy metal-contaminated soil.

Control of nitrogen and odor emissions during chicken manure composting with a carbon-based microbial inoculant and a biotrickling filter

Although aerobic composting is usually utilized in livestock manure disposal, the emission of odorous gases from compost not only induces harm to the human body and the environment, but also causes loss of nitrogen, sulfur, and other essential elements, resulting in a decline in product quality. The impact of biotrickling filter (BTF) and insertion of carbon-based microbial agent (CBMA) on compost maturation, odor emissions, and microbial population during the chicken manure composting were assessed in the current experiment. Compared with the CK group, CBMA addition accelerated the increase in pile temperature (EG group reached maximum temperature 10 days earlier than CK group), increased compost maturation (GI showed the highest increase of 41.3% on day 14 in EG group), resulted in 36.59% and 14.60% increase in NO3--N content and the total nitrogen retention preservation rate after composting. The deodorization effect of biotrickling filter was stable, and the removal rates of NH3, H2S, and TVOCs reached more than 90%, 96%, and 56%, respectively. Furthermore, microbial sequencing showed that CBMA effectively changed the microbial community in compost, protected the ammonia-oxidizing microorganisms, and strengthened the nitrification of the compost. In addition, the nitrifying and denitrifying bacteria were more active in the cooling period than they were in the thermophilic period. Moreover, the abundance of denitrification genes containing nirS, nirK, and nosZ in EG group was lower than that in CK group. Thus, a large amount of nitrogen was retained under the combined drive of BTF and CBMA during composting. This study made significant contributions to our understanding of how to compost livestock manure while reducing releases of odors and raising compost quality.