Effect of bioaugmentation on lignocellulose degradation and antibiotic resistance genes removal during biogas residues composting

Antibiotic resistance genes in anaerobic digestion: Unresolved challenges and potential solutions

Antimicrobial resistance (AMR) threatens public health, necessitating urgent efforts to mitigate the global impact of antibiotic resistance genes (ARGs). Anaerobic digestion (AD), known for volatile solid reduction and energy generation, also presents a feasible approach for the removal of ARGs. This review encapsulates the existing understanding of ARGs and antibiotic-resistant bacteria (ARB) during the AD process, highlighting unresolved challenges pertaining to their detection and quantification. The questions raised and discussed include: Do current ARGs detection methods meet qualitative and quantitative control requirements? How can we conduct risk assessments of ARGs? What happens to ARGs when they come into co-exposure with other emerging pollutants? How can the application of internal standards bolster the reliability of the AD resistome study? What are the potential future research directions that could enhance ARG elimination? Investigating these subjects will assist in shaping more efficient management strategies that employ AD for effective ARG control.

Pathway of typical β-Lactam antibiotics degradation by black soldier fly and response characteristic of its intestinal microbes

To effectively address the contamination caused by antibiotic misuse, this study was conducted to enhance the removal of amoxicillin (AMX) and penicillin sodium (PEN) by incorporating black soldier fly larvae (BSFL). The results showed that BSFL increased the degradation rates of AMX and PEN to 71.00 % and 80.89 %, respectively, and shortened their half-lives to 238 h and 160 h. Proteobacteria (26.2 %-82.0 %), Firmicutes (13.3 %-54.0 %), Acinobacteriota (2.1 %-23.4 %), and Bacteroidota (1.3 %-10.1 %) were the intestinal dominant microorganisms during transformation. Five bacteria with β-lactam antibiotic resistance in the BSFL gut were isolated, among which Morganella morganii demonstrated strong antibiotic tolerance and high removal rates of AMX and PEN in both in vitro and in vivo experiments, ranging from 58.99 % to 95.87 %. BSFL intestinal bacteria disrupted the quaternary pharmacophore of AMX and PEN, breaking them down into at least seven and five metabolites, respectively.

Enhancing degradation of antibiotic-combined pollutants by a hybrid system containing advanced oxidation and microbial treatment, a review

Antibiotics often co-exist with other pollutants, posing a significant threat to ecosystems. This review first examines the applications and limitations of microbial treatments for various types of antibiotic-combined pollutants. Then, it explores the mechanisms and application of hybrid systems that integrate advanced oxidation with microbial treatment, categorized into two-stage and intimately hybrid systems. Finally, the review highlights key knowledge gaps in hybrid systems and provides new insight into the removal of combined pollutants.

Application of microbial agents in organic solid waste composting: a review

The rapid growth of organic solid waste has recently exacerbated environmental pollution problems, and its improper treatment has led to the loss of a large number of biomass resources. Here, we expound the advantages of microbial agents composting compared with conventional organic solid waste treatment technology, and review the important role of microbial agents composting in organic solid waste composting from the aspects of screening and identification, optimization of conditions, mechanism of action, combination with other technologies and ultra-high-temperature and ultra-low-temperature microbial composting. We discuss the value of microorganisms with different growth conditions in organic solid waste composting, and put forward a seasonal multi-temperature composite microbial composting technology. Provide new ideas for the all-round treatment of microbial agents in organic solid waste in the future. © 2024 Society of Chemical Industry.

High acidity organic waste degradation and the potential to bioremediation of heavy metals in soil by an acid-tolerant Serratia sp

Highly acidic citrus pomace (CP) is a byproduct of Pericarpium Citri Reticulatae production and causes significant environmental damage. In this study, a newly isolated acid-tolerant strain of Serratia sp. JS-043 was used to treat CP and evaluate the effect of reduced acid citrus pomace (RACP) in passivating heavy metals. The results showed that biological treatment could remove 97.56% of citric acid in CP, the organic matter in the soil increased by 202.60% and the catalase activity in the soil increased from 0 to 0.117 U g-1. Adding RACP into soil can increase the stabilization of Cu, Zn, As, Co, and Pb. Specifically, through the metabolism of strain JS-043, RACP was also involved in the stabilization of Zn and Pb, and Residual Fraction in the total pool of these metals increased by 10.73% and 10.54%, respectively. Finally, the genome sequence of Serratia sp. JS-043 was completed, and the genetic basis of its acid-resistant and acid-reducing characteristics was preliminarily revealed. JS-043 also contains many genes encoding proteins associated with heavy metal ion tolerance and transport. These findings suggest that JS-043 may be a high-potential strain to improve the quality of acidic organic wastes that can then be useful for soil bioremediation.

Simultaneous removal of ammonia nitrogen, phosphate, zinc, and phenol by degradation of cellulose in composite mycelial pellet bioreactor: Enhanced performance and community co-assembly mechanism

In this experiment, the prepared tea biochar-cellulose@LDH material (TB-CL@LDH) was combined with mycelium pellets to form the composite mycelial pellets (CMP), then assembled and immobilized with strains Pseudomonas sp. Y1 and Cupriavidus sp. ZY7 to construct a bioreactor. At the best operating parameters, the initial concentrations of phosphate (PO43--P), ammonia nitrogen (NH4+-N), chemical oxygen demand (COD), zinc (Zn2+), and phenol were 22.3, 25.0, 763.8, 1.0, and 1.0 mg L-1, the corresponding removal efficiencies were 80.4, 87.0, 83.4, 91.8, and 96.6%, respectively. Various characterization analyses demonstrated that the strain Y1 used the additional carbon source produced by the strain ZY7 degradation of cellulose to enhance the removal of composite pollutants and clarified the principle of Zn2+ and PO43--P removal by adsorption, co-precipitation and biomineralization. Pseudomonas and Cupriavidus were the dominant genera according to the high-throughput sequencing. As shown by KEGG results, nitrification and denitrification genes were affected by phenol. The study offers prospects for the simultaneous removal of complex pollutants consisting of NH4+-N, PO43--P, Zn2+, and phenol.

Bioaugmentation of anaerobic digesters with the enriched lignin-degrading microbial consortia through a metagenomic approach

The recalcitrance of lignin impedes the efficient utilization of lignocellulosic biomass, hindering the efficient production of biogas and value-added materials. Despite the emergence of anaerobic digestion as a superior alternative to the aerobic method for lignin processing, achieving its feasibility requires thorough characterization of lignin-degrading anaerobic microorganisms, assessment of their biomethane production potential, and a comprehensive understanding of the degradation pathway. This study aimed to address the aforementioned necessities by bioaugmenting seed sludge with three distinct enriched lignin-degrading microbial consortia at both 25 °C and 37 °C. Enhanced biomethane yields was detected in the bioaugmented digesters, while the highest production was observed as 188 mLN CH4 gVS-1 in digesters operated at 37 °C. Moreover, methane yield showed a significant improvement in the samples at 37 °C ranging from 110% to 141% compared to the control, demonstrating the efficiency of the enriched lignin-degrading microbial community. Temperature and substrate were identified as key factors influencing microbial community dynamics. The observation that microbial communities tended to revert to the initial state after lignin depletion, indicating the stability of the overall microbiota composition in the digesters, is a promising finding for large-scale studies. Noteworthy candidates for lignin degradation, including Sporosarcina psychrophila, Comamonas aquatica, Shewanella baltica, Pseudomonas sp. C27, and Brevefilum fermentans were identified in the bioaugmented samples. PICRUSt2 predictions suggest that the pathway and specific proteins involved in anaerobic lignin degradation might share similarities with those engaged in the degradation of aromatic compounds.

Co-composting of green waste and biogas waste: physical, chemical parameters and quality of ripe compound

The impact of adding biogas waste (BW) to green waste (GW) composting to increase nitrogen supplementation and improve mature compost quality was investigated. Conducted over 90 days using static windrows, the experiment compared treatments with GW alone (T1) and GW supplemented with BW (T2 and T3). The results showed that the addition of BW increased temperatures, improved the C/N ratio, and expedited the stabilization process compared to T1. Furthermore, the addition of BW led to significant degradation of hemicellulose (up to 39.98%) and cellulose (up to 27.63%) compared to GW alone. Analysis of Fourier-transform infrared (FTIR) spectra revealed the presence of aromatic, phenolic, aliphatic, and polysaccharide structures in the compost, with BW supplementation enhancing these characteristics. Importantly, the germination index (GI) assessment indicated that the compounds produced were not toxic and instead exhibited stimulatory effects on seed germination. Overall, the findings suggest that supplementing GW composting with BW can enhance the quality and efficacy of the composting process, resulting in compost with desirable properties for agricultural use.

Effects of micro-nano bubble water addition on maturation degree and microbial community during aerobic composting

In order to explore the effects of micro-nano bubble water (MNBW) on compost maturation and the microbial community in cow manure and straw during aerobic composting, we conducted composting tests using tap water with 12 mg/L (O12), 15 mg/L (O15), 18 mg/L (O18), and 21 mg/L (O21) dissolved oxygen in MNBW, as well as tap water with 9 mg/L dissolved oxygen as a control (CK). The results showed that O21 increased the maximum compost temperature to 64 °C, which was higher than the other treatments. All treatments met the harmless standards for compost. The seed germination index (GI) was largest under O21 and 15.1% higher than that under CK, and the non-toxic compost degree was higher. Redundancy analysis showed that the temperature, C/N, pH, and GI were important factors that affected the microbial community composition. The temperature, C/N, and pH were significantly positively correlated with Firmicutes and Actinobacteria (p < 0.05). Firmicutes was the dominant phylum in the mesophilic stage (2-6 days) and it accounted for a large proportion under O21, where the strong thermophilic metabolism increased the production of heat and prolonged the high temperature period. The bacterial genus Ammoniibacillus in Firmicutes accounted for a large proportion under O21 and it accelerated the decomposition of substrates. Therefore, the addition of MNBW changed the microbial community to affect the maturation of the compost, and the quality of the compost was higher under O21.

Effect of microbial inoculum on composting efficiency in the composting process of spent mushroom substrate and chicken manure

This work aimed to investigate the microbial mechanisms for the improvement of composting efficiency driven by the compound microbial inoculum (MI) (Bacillus subtilis SL-44, Enterobacter hormaechei Rs-189 and Trichoderma reesei) during co-composting of spent mushroom substrate (SMS) and chicken manure (CM). The treatments used in the study were as follows: 1) MI (inoculation with microbial inoculum), 2) CI (inoculation with commercial microbial inoculum), and 3) CK (without inoculation). The results demonstrated that MI increased the seed germination index (GI) by 25.11%, and contents of humus, humic acid (HA) and available phosphorus (AP) were correspondingly promoted by 12.47%, 25.93% and 37.16%, respectively. The inoculation of MI increased the temperature of the thermophilic stage by 3-7 °C and achieved a cellulose degradation rate of 52.87%. 16S rRNA gene analysis indicated that Actinobacteria (11.73-61.61%), Firmicutes (9.46-65.07%), Proteobacteria (2.86-32.17%) and Chloroflexi (0.51-10.92%) were the four major phyla during the inoculation composting. Bacterial metabolic functional analysis revealed that pathways involved in amino acid and glycan biosynthesis and metabolism were boosted in the thermophilic phase. There was a positive correlation between bacterial communities and temperature, humification and phosphorus fractions. The average dry weight, fresh weight and seedling root length in the seedling substrates adding MI compost were 1.13, 1.23 and 1.06 times higher than those of the CK, respectively. This study revealed that biological inoculation could improve the composting quality and efficiency, potentially benefiting the resource utilization of agricultural waste resources.

Effect of simplified inoculum agent on performance and microbiome during cow manure-composting at industrial-scale

A simplified inoculum agent, only comprising Bacillus subtilis and Aspergillus niger, was utilized for industrial-scale cow-manure composting to investigate its impact on composting performance and microbiome. Inoculants elevated the average and peak temperatures by up to 7 and 10 °C, respectively, during the thermophilic stage, reduced organic matter content, and raised germination index. Inoculation also extended the period of composting above 50 °C from 12 to 26 days. Sequencing unveiled significant shifts in microbial diversity, composition, and function. Aspergillus thrived during the mesophilic phase, potentially initiating composting, whereas Bacillus, Lysinibacillus, and Clostridium were enriched during the thermophilic stage. Metagenomic sequencing revealed an increased abundance of carbohydrate-active enzymes and glycometabolism-related genes responsible for lignocellulose degradation and heat generation after inoculation. These enriched microbes and functional genes contributed to organic matter degradation and temperature maintenance during thermophilic stage, expediting composting. This suggests the effectiveness of this simplified inoculum in industrial-level cow-manure composting.

Enhanced humus synthesis from Chinese medicine residues composting by lignocellulose-degrading bacteria stimulation: Upregulation of key enzyme activity and neglected indirect effects on humus formation

Chinese medicine residues (CMHRs) resource is attracting widespread attention, as it is expected to be produced into Humus-rich fertilizer for soil application. This study aimed to promote effective humus (HS) production through lignocellulose-degrading bacteria (LDB) addition and explore the biological regulation mechanism of LDB affecting lignocellulose-to-humus conversion. The results showed higher HS production was achieved, with 109.73 and 111.44 g·kg-1, and HA/FA was raised by 12.70-16.02 % in compost products by LDB addition stimulation. Significant upregulation of β-glucanase and xylanase activities catalyzed higher decomposition of lignocellulose toward more HS potential precursors supply. Furthermore, exogenous LDB intervention induced microbial community restructure and microbial network establishment via enriching synergism functional bacteria, i.e., Thermobifida, Paenibacillus, Nonomuraea, etc. Mantel test results showed that it was variation of cellulose, hemicellulose and HS that affected microbial community succession (p < 0.01, r > 0.6), which represented the positive action of LDB addition stimulation on HS synthesis upregulation. Further exploration suggested LDB had an indirect effect on HS formation by enhanced lignin and hemicellulose conversion based on the Random Forest model and Partial least-squares path modeling results. This research provides new insights into the trigger effects of LDB introduction on upregulating HS synthesis and is expected to propose new perspectives for HS efficient production in CMHRs composting.

Electric field as extracellular enzyme activator promotes conversion of lignocellulose to humic acid in composting process

To promote efficient conversion of lignocellulose to humus (HS) during composting, a novel bio-electrochemical technology was applied and explored the effect and mechanism of electrification on carbon conversion during different composting periods. The results showed that supplementary electric field played different roles during composting. In the early stage, organic matter mineralization was significantly accelerated under electric field application, that was embodied in a 29.8% increase of CO2 emission due to the enhanced metabolic activity of microorganisms. However, the electric field functioned as an extracellular enzyme activator during the later stage since the abundance of functional microorganisms related to lignocellulose degradation was increased by 1.5-2.8 fold that effectively promoted the conversion of lignocellulose to HS. The humic acid content of the compost products increased by 23.0-32.9% compared with control. This study elucidated how electric fields affect carbon conversion during composting, which provides a novel strategy for returning agricultural wastes to soil.

Occurrence and fate of antibiotics in swine waste treatment: An industrial case

This study mapped the fate of antibiotics in a swine farm with integrated waste treatment including anoxic stabilization, fixed-film anaerobic digestion, anoxic-oxic (A/O), and composting. Results show the prevalent and consistent occurrence of 12 antibiotics in swine waste. Mass balance of these antibiotics was calculated to track their flow and evaluate their removal by different treatment units. The integrated treatment train could effectively reduce antibiotic loading to the environment by 90% (measured as combined mass of all antibiotic residues). Within the treatment train, anoxic stabilization as the initial treatment step, accounted for the highest contribution (43%) to overall antibiotic elimination. Results also show that aerobic was more effective than anaerobic regarding antibiotic degradation. Composting accounted for an additional of 31% removal of antibiotics while anaerobic digestion contributed to 15%. After treatment, antibiotic residues in the treated effluent and composted materials were 2 and 8% of the initial antibiotic loading in raw swine waste, respectively. Ecological risk assessment showed negligible or low risk quotient associated with most individual antibiotics released into the aquatic environment or soil from swine farming. Nevertheless, antibiotic residues in treated water and composted materials together showed significant ecological risk to water and soil organisms. Thus, further work to improve treatment performance or develop new technologies is necessary to reduce the impact of antibiotics from swine farming.

Reduction of metronidazole in municipal wastewater and protection of activated sludge system using a novel immobilized Aspergillus tabacinus LZ-M

Metronidazole (MNZ) accumulation inhibits municipal wastewater treatment bio-systems, and an effective solution to augment anaerobic activated sludge (AAS) is required. This research discovered that Aspergillus tabacinus LZ-M could degrade 77.39% of MNZ at 5 mg/L. MNZ was metabolized into urea, and the enzymes involved in its degradation were aminotransferase, methyltransferase, monooxygenase, and CN cleavage hydrolase. The strain was immobilized in polyurethane foam and used in AAS for the treatment of MNZ-containing municipal wastewater. The results showed that, using immobilized LZ-M, MNZ was completely removed, and the degradation efficiency of wastewater's chemical oxygen demand (COD) was increased from 11.7% to 83.31%. The extracellular polymer and ROS levels indicated that MNZ's toxicity on AAS was reduced. Furthermore, bioaugmentation stabilized its microbial community, and decreased MNZ resistance genes. These observations confirm that the immobilized fungi are effective in protecting AAS against antibiotic contamination in the treatment process of municipal wastewater.

A newly developed consortium with a highly efficient thiocyanate degradation capacity: A comprehensive investigation of the degradation and detoxification potential

Thiocyanate-containing wastewater harms ecosystems and can cause serious damage to animals and plants, so it is urgent to treat it effectively. In this study, a new efficient thiocyanate-degrading consortium was developed and its degradation characteristics were studied. It was found that up to 154.64 mM thiocyanate could be completely degraded by this consortium over 6 days of incubation, with a maximum degradation rate of 1.53 mM h^-1. High-throughput sequencing analysis showed that Thiobacillus (77.78%) was the predominant thiocyanate-degrading bacterial genus. Plant toxicology tests showed that the germination index of mung bean and rice seeds cultured with media obtained after thiocyanate degradation by the consortium increased by 94% and 84.83%, respectively, compared with the control group without thiocyanate degradation. Cytotoxicity tests showed that thiocyanate without degradation significantly decreased the Neuro-2a cell activity and mitochondrial membrane potential; induced reactive oxygen species generation and apoptosis; increased the cellular Ca²⁺ concentration; and damaged the cell nucleus and DNA. Furthermore, the thiocyanate degradation products produced the consortium were almost totally non-toxic, revealing the same characteristics as those of the control using distilled water. This study shows that the consortium has a high degradation efficiency and detoxification characteristics, as well as great application potential in bioremediation of industrial thiocyanate-containing wastewater.

Recent advances in metagenomic analysis of different ecological niches for enhanced biodegradation of recalcitrant lignocellulosic biomass

Lignocellulose wastes stemming from agricultural residues can offer an excellent opportunity as alternative energy solutions in addition to fossil fuels. Besides, the unrestrained burning of agricultural residues can lead to the destruction of the soil microflora and associated soil sterilization. However, the difficulties associated with the biodegradation of lignocellulose biomasses remain as a formidable challenge for their sustainable management. In this respect, metagenomics can be used as an effective option to resolve such dilemma because of its potential as the next generation sequencing technology and bioinformatics tools to harness novel microbial consortia from diverse environments (e.g., soil, alpine forests, and hypersaline/acidic/hot sulfur springs). In light of the challenges associated with the bulk-scale biodegradation of lignocellulose-rich agricultural residues, this review is organized to help delineate the fundamental aspects of metagenomics towards the assessment of the microbial consortia and novel molecules (such as biocatalysts) which are otherwise unidentifiable by conventional laboratory culturing techniques. The discussion is extended further to highlight the recent advancements (e.g., from 2011 to 2022) in metagenomic approaches for the isolation and purification of lignocellulolytic microbes from different ecosystems along with the technical challenges and prospects associated with their wide implementation and scale-up. This review should thus be one of the first comprehensive reports on the metagenomics-based analysis of different environmental samples for the isolation and purification of lignocellulose degrading enzymes.

Boosting Hydrolysis of Cellulose at High Temperature by β-Glucosidase Induced Metal-Organic Framework In-Situ Co-Precipitation Encapsulation

Due to the poor enzyme thermal stability, the efficient conversion of high crystallinity cellulose into glucose in aqueous phase over 50 °C is challenging. Herein, an enzyme-induced MOFs encapsulation of β-glucosidase (β-G) strategy was proposed for the first time. By using various methods, including SEM, XRD, XPS, NMR, FTIR and BET, the successful preparation of a porous channel-type flower-like enzyme complex (β-G@MOFs) was confirmed. The prepared enzyme complex (β-G@MOFs) materials showed improved thermal stability (from 50 °C to 100 °C in the aqueous phase) and excellent resistance to ionic liquids (the reaction temperature was as high as 110 °C) compared to the free enzyme (β-G). Not only the catalytic hydrolysis of cellulose by single enzyme (β-G) in ionic liquid was realized, but also the high-temperature continuous reaction performance of the enzyme was significantly improved. Benefiting from the significantly improved heat resistance, the β-G@MOFs exhibited 32.1 times and 34.2 times higher enzymatic hydrolysis rate compared to β-G for cellobiose and cellulose substrates, respectively. Besides, the catalytic activity of β-G@MOFs was retained up to 86 % after five cycles at 110 °C. This was remarkable because the fixation of the enzyme by the MOFs ensured that the folded structure of the enzyme would not expand at high temperatures, allowing the native conformation of the encapsulated protein well-maintained. Furthermore, we believe that this structural stability was caused by the confinement of flower-like porous MOFs.

Deciphering the fate of antibiotic resistance genes in norfloxacin wastewater treated by a bio-electro-Fenton system

The misuse of antibiotics has increased the prevalence of antibiotic resistance genes (ARGs), considered a class of critical environmental contaminants due to their ubiquitous and persistent nature. Previous studies reported the potentiality of bio-electro-Fenton processes for antibiotic removal and ARGs control. However, the production and fate of ARGs in bio-electro-Fenton processes triggered by microbial fuel cells are rare. In this study, the norfloxacin (NFLX) average residual concentrations within two days were 2.02, 6.07 and 14.84 mg/L, and the average removal efficiency of NFLX was 79.8 %, 69.6 % and 62.9 % at the initial antibiotic concentrations of 10, 20 and 40 mg/L, respectively. The most prevalent resistance gene type in all processes was the fluoroquinolone antibiotic gene. Furthermore, Proteobacteria was the dominant ARG-carrying bacteria. Overall, this study can provide theoretical support for the efficient treatment of high antibiotics-contained wastewater by bio-electro-Fenton systems to better control ARGs from the perspective of ecological security.

Evaluation of fungal community assembly and function during food waste composting with Aneurinibacillus sp. LD3 inoculant

The objective of this work was to evaluate the fungal community assembly and function during food waste composting with Aneurinibacillus sp. LD3 (LD3) inoculant. Inoculation reduced the content of total organic carbon, moisture content, nitrate nitrogen, and nitrite nitrogen. The LD3 inoculant was able to drive the changes in the assembly of the fungal community. In particular, inoculation with LD3 not only increased the relative abundance of Ascomycota and Trichocomaceae_unclassified for lignocellulose degradation at the mesophilic and cooling stages but also reduced the relative abundances of the opportunistic human pathogen Candida. Saprotroph was the predominant fungal trophic mode in composting, and inoculation with LD3 has a better inactivation effect on animal and plant pathogenic fungi during composting. Furthermore, the variation of the fungal community after inoculation with LD3 was the largest explained by temperature (30.64%). These results implied that LD3 significantly regulated fungal composition and function of food waste composting.

Effects of 3D-printed bulking agent on microbial community succession and carbohydrate-active enzymes genes during swine manure composting

The bulking agent plays an important role in aerobic composting, but their shape, porosity, and homogeneity need to be optimized. In the present work, a bulking agent with a uniform shape was prepared by 3D printing to explore its influence on physicochemical parameters, microbial community succession, and gene abundance of carbohydrate-active enzymes (CAZymes) in swine manure aerobic composting. The results showed that adding 3D-printed bulking agents can increase maximum temperature, prolong the thermophilic period, and improve the degradation rate of volatile solids, which was attributed to ameliorative air permeability by the porous 3D-printed bulking agent. The abundances of some pathogenic bacteria decreased and CAZymes genes increased respectively in response to the addition of the 3D-printed bulking agent, implying it has a certain positive effect on improving the safety of compost products and promoting the degradation of organic matter. In summary, the 3D-printed bulking agent has good application potential in laboratory-scale aerobic composting.

Exploring the dynamic of microbial community and metabolic function in food waste composting amended with traditional Chinese medicine residues

The aim of this study was to explore the dynamic of microbial community and metabolic function in food waste composting amended with traditional Chinese medicine residues (TCMRs). Results suggested that TCMRs addition at up to 10% leads to a higher peak temperature (60.5 °C), germination index (GI) value (119.26%), and a greater reduction in total organic carbon (TOC) content (8.08%). 10% TCMRs significantly induced the fluctuation of bacterial community composition, as well as the fungal community in the thermophilic phase. The addition of 10% TCMRs enhanced the abundance of bacterial genera such as Acetobacter, Bacillus, and Brevundimonas, as well as fungal genera such as Chaetomium, Thermascus, and Coprinopsis, which accelerated lignocellulose degradation and humification degree. Conversely, the growth of Lactobacillus and Pseudomonas was inhibited by 10% TCMRs to weaken the acidic environment and reduce nitrogen loss. Metabolic function analysis revealed that 10% TCMRs promoted the metabolism of carbohydrate and amino acid, especially citrate cycle, glycolysis/gluconeogenesis, and cysteine and methionine metabolism. Redundancy analysis showed that the carbon to nitrogen (C/N) ratio was the most significant environmental factor influencing the dynamic of bacterial and fungal communities.

Accelerated stabilization of high solid sludge by thermal hydrolysis pretreatment in autothermal thermophilic aerobic digestion (ATAD) process

Autothermal thermophilic aerobic digestion (ATAD) is a rapid biological treatment technology for sludge stabilization. To improve digestion efficiency and shorten stabilization time, thermal hydrolysis pretreatment was employed before ATAD of high solid sludge. The results showed that accelerated stabilization of high solid sludge (total solid = 10.1%) was achieved by thermal hydrolysis pretreatment with volatile solid removal efficiency of 40.3% after 8 days of ATAD, 11 days earlier than unpretreated sludge. The enhanced release and hydrolysis of intracellular organics resulted in a solubilization degree of 45.3%. The reduced sludge viscosity and improved fluidity after thermal hydrolysis facilitated mixing, aeration and organics degradation during ATAD. Excitation emission matrix analysis indicated that the fluorescence intensity of soluble microbial byproduct and tyrosine-like protein increased markedly after thermal hydrolysis and decreased after ATAD. The proportion of high molecular weight (MW > 10 kDa) substances in the supernatant increased significantly after thermal hydrolysis, while the low MW (MW < 1 kDa) substances decreased after ATAD. The significant difference in microbial composition between the pretreatment and control groups elucidated the accelerated sludge stabilization under thermal hydrolysis. This work provides an efficient and practical strategy to achieve rapid stabilization of high solid sludge.

Impact of composting factors on the biodegradation of lignin in Eichhornia crassipes (water hyacinth): A response surface methodological (RSM) investigation

Water hyacinth (Eichhornia crassipes) is a hydrophyte weed that causes havoc in the aquatic ecosystem as an invasive plant that can obstruct waterways and bring about nutrient imbalance. This study aims to address how this invasive hydrophyte can be physically harvested and biochemically transformed into a bioproduct that can enhance the restoration of damaged soil. Biocomposting, a low-cost biotechnological technique, was designed to degrade the lignocellulosic Eichhornia crassipes biomass and transform it into a valuable bioproduct. The process used response surface methodology (RSM) to investigate the aggregate effect of moisture content, turning frequency, and microbial isolate (Chitinophaga terrae) inoculum size on the breakdown of lignin over 21 days. The moisture content (A), (45, 55, 65) % v/w, inoculum size (B), (5, 7.5, 10)% v/v, and turning frequency (C), (1, 3, 5) days were considered independent variables, while percentage lignin degradation was considered a response variable. The optimal conditions for lignin breakdown were 65.7 percent (v/w) moisture, 7.5 percent (v/v) inoculum concentration, and 5-day interval turning. The R2 score of 0.9733 demonstrates the model's integrity and reliability. Thus, the RSM approach resulted in a fine grain dark brown Nutri-compost that proved effective in enhancing soil fertility. This procedure is recommended for a scale-up process where large quantities of the hydrophyte could be treated for conversion into Nutri compost.

Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting

This study examined the effects of biochar, biogas residue, and their combined amendments on CO₂ and CH₄ emission, enzyme activity, and related functional genes during rice straw composting. Results showed that the biogas residue increased CO₂ and CH₄ emissions by 13.07 % and 74.65 %, while biochar had more obvious inhibition. Biogas residue addition enhanced functional gene abundance more than biochar. Biogas residue raised the methanogens mcrA gene by 2.5 times. Biochar improved the Acetyl-CoA synthase and β-glucosidase activities related to carbon fixation and decreased coenzyme activities related to methanogens. Biochar and biogas residue combined amendments enhanced the acsB gene abundance for CO₂ assimilation process and decreased methyl-coenzyme M reductase α subunit activity. Pearson correlation analysis indicated that organic matter was the significant variable affecting CO₂ and CH₄ emissions (P < 0.01). These results indicated biochar played significant roles in carbon loss and greenhouse emissions caused by biogas residue incorporation during composting.

Insights into the effect of iron-carbon particle amendment on food waste composting: Physicochemical properties and the microbial community

The effects of iron-carbon (Fe-C) particle amendment on organic matter degradation, product quality and functional microbial community in food waste composting were investigated. Fe-C particles (10%) were added to the material and composted for 32 days in a lab-scale composting system. The results suggested that Fe-C particle enhanced organic matter degradation by 12.3%, particularly lignocellulose, leading to a greater humification process (increased by 15.5%). In addition, NO₃^--N generation was enhanced (15.9%) by nitrification with more active ammonia monooxygenase and nitrite oxidoreductase activities in the cooling and maturity periods. Fe-C particles not only significantly increased the relative abundances of Bacillus and Aspergillus for organic matter decomposition, but also decreased the relative abundances of acid-producing bacteria. RDA analysis demonstrated that the bacterial community was significantly influenced by dissolved organic matter, C/N, NO₃^--N, humic acid, volatile fatty acids and pH, while electrical conductivity was the key factor affecting the fungal community.

Integrated meta-omics study on rapid tylosin removal mechanism and dynamics of antibiotic resistance genes during aerobic thermophilic fermentation of tylosin mycelial dregs

For efficient treatment of tylosin mycelial dregs (TMDs), rapid tylosin removal mechanism and dynamics of ARGs during TMDs fermentation were investigated using integrated meta-omics (genomics, metaproteomics and metabolomics) and qPCR approaches. The results showed that over 86% of tylosin was degraded on day 7 regardless of the type of bulking agents. The rapid removal of tylosin was mainly attributed to de-mycarose reaction (GH3) and esterase hydrolysis (C7MYQ7) of Saccharomonospora, and catalase-peroxidase oxidation of Bacillus (A0A077JB13). In addition, the moisture content and mobile genetic elements were vital to control the rebound of ARGs. The removal efficiency of antibiotic resistant bacteria (Streptomyces, Pseudomonas, norank_f__Sphingobacteriaceae, and Paenalcaligenes) and Intl1 (98.8%) in fermentation treatment TC21 with corncob as the bulking agent was significantly higher than that in other three treatments (88.3%). Thus, appropriate bulking agents could constrain the abundance of antibiotic resistant bacteria and Intl1, which is crucial to effectively reduce the resistance.

The microbial mechanisms of enhanced humification by inoculation with Phanerochaete chrysosporium and Trichoderma longibrachiatum during biogas residues composting

This study investigated effects of composite microbes (CMs) (Phanerochaete chrysosporium and Trichoderma longibrachiatum) on humification during co-composting of biogas residue, spent mushroom substrate and rice straw. Results showed that CMs inoculation elevated degradation ratios of cellulose, hemicellulose and lignin by 7.86%, 8.87% and 6.45%, and contents of humus and humic acid were correspondingly promoted by 15.5% and 23.6%, respectively. Relative abundances of bacteria associated with refractory macromolecules degradation (Flavobacterium, Anseongella and Actinomadura) and cellulolytic fungi (Hypocreales_Incertae_sedis, Hypocreaceae and Psathyrellaceae) were raised by CMs addition. Redundancy analysis demonstrated a positive correlation between microbial communities and temperature, fulvic acid and lignocellulose contents. Moreover, CMs inoculation promoted pathways of xenobiotics biodegradation and metabolism, and biosynthesis of other secondary metabolites, which was closely associated with lignocellulose degradation and humus formation. These results suggested that biological inoculation could enhance composting efficiency and improve compost quality, benefiting biogas residues composting.

Effect of micronutrient selenium on greenhouse gas emissions and related functional genes during goat manure composting

To explore the effect of microelement selenium on greenhouse gas emission, nitrogen loss and related functional genes during the composting. Selenite and selenate were respectively mixed with goat manure and wheat straw and then composted the mixture without selenium regarded as control. The results indicated adding selenite prolonged the thermophilic phase and improved the organic matter degradation, while the selenate presented the opposite results. Selenite and selenate influenced ammonium transformation while prompting the formation of nitrate. Compared to the control, adding selenite and selenate both decreased NH₃ emissions (by 26.7%-53.1%) and increased the total nitrogen content of compost. The addition of selenium increased mcrA in the early phase of composting, thereby promoting CH₄ emission (by 3.5-18.4%). Meanwhile, adding selenate significantly reduced nirK abundance and consequently reduced N₂O emission. Moreover, selenate added treatment presented the highest compost maturity (88.77%) and the lowest global warm potential (117.46 g/kg CO₂-eq.) among all treatments.

Compost-derived indole-3-acetic-acid-producing bacteria and their effects on enhancing the secondary fermentation of a swine manure-corn stalk composting

Composting, as an effectively bio-oxidative process, has been widely used for converting organic waste to organic fertilizer. However, the low fertilizer efficiency of composting product limited its application in agriculture. To improve the growth-promoting effect of composting product, the present study investigated the bioaugmentation strategy of inoculating indole-3-acetic-acid (IAA)-producing bacteria. Firstly, two IAA-producing bacteria (Bacillus safensis 33C and Rhodococcus rhodochrous YZ) were isolated from composting products with high IAA yields of 39.18 and 16.32 μg mL^-1, respectively. Secondly, the microbial inoculants were prepared with 33C, YZ and a previously isolated IAA-producing strain Corynebacterium stationis 29B. To increase the accumulation of microbial secondary metabolites, microbial inoculants were amended at the secondary fermentation stage of composting. Physicochemical characterization showed that the maturity of composting product was significantly promoted by inoculating microbial inoculants prepared with 33C and 29B (single and combined inoculants). Finally, bioaugmentation with 33C and 29B increased the IAA contents of composting products by 2.9-5.2 times, which benefited the germination and early vegetative growth of plants. In summary, inoculating proper IAA-producing bacteria during secondary fermentation of composting could improve the quality of composting product and expand its application.

Influence of microbial inoculants on co-composting of lignocellulosic crop residues with farm animal manure: A review

The rapidly developing agro-industry generates huge amounts of lignocellulosic crop residues and animal manure worldwide. Although co-composting represents a promising and cost-effective method to treat various agricultural wastes simultaneously, poor composting efficiency prolongs total completion time and deteriorates the quality of the final product. However, supplementation of the feedstock with beneficial microorganisms can mitigate these negative effects by facilitating the decomposition of recalcitrant materials, enhancing microbial enzyme activity, and promoting maturation and humus formation during the composting process. Nevertheless, the influence of microbial inoculation may vary greatly depending on certain factors, such as start-up parameters, structure of the feedstock, time of inoculation, and composition of the microbial cultures used. The purpose of this contribution is to review recent developments in co-composting procedures involving different lignocellulosic crop residues and farm animal manure combined with microbial inoculation strategies. To evaluate the effectiveness of microbial additives, the results reported in a large number of peer-reviewed articles were compared in terms of composting process parameters (i.e., temperature, microbial activity, total organic carbon and nitrogen contents, decomposition rate of lignocellulose fractions, etc.) and compost characteristics (humification, C/N ratio, macronutrient content, and germination index). Most studies confirmed that the use of microbial amendments in the co-composting process is an efficient way to facilitate biodegradation and improve the sustainable management of agricultural wastes. Overall, this review paper provides insights into various inoculation techniques, identifies the limitations and current challenges of co-composting, especially with microbial inoculation, and recommends areas for further research in this field.