Bioaugmentation mechanism on humic acid formation during composting of food waste

The effect of auxiliary conditioning on humification of high-solids anaerobic digestion residues in aerobic composting processes

This study investigated the impact of cornstalk, bagasse, and spent mushroom substrate (SMS) as auxiliary materials on the nitrogen cycling and humification during the aerobic composting of high-solids anaerobically digested residues using high-throughput 16S rRNA sequencing and PICRUSt2 functional prediction. Results showed that cornstalk and SMS accelerated compost warming and upregulated the expression of nitrogen-cycling-related genes (e.g. ureC, narH, and narG), thereby significantly reducing (P < 0.05) N2O and NH3 emissions and increasing the NO3--N content in the compost. Furthermore, cornstalk enriched the microbial diversity and abundance of key bacteria involved in degradation and humification (e.g. Sphingobacterium and Moheibacter), which increased the humic acid content (HA) (78.4 g/kg DM). Although bagasse promoted aerobic conditions, it had less effect on nitrogen cycling and humification. The study highlights the intricate relationship between nitrogen metabolism and humification, demonstrating how selection of auxiliary materials can optimize composting for environmental sustainability.

Fe2O3@D201 Enhanced Efficiency of Food Waste Degradation by Microbial Inoculum Under Aerobic Condition

The global quantity of food waste (FW) is increasing at an alarming rate, making safe disposal a pressing issue in urban management. The inappropriate disposal of FW will put risks on health and environment. Aerobic degradation equipment has emerged as a promising solution for FW disposal by adding microbial agents. However, current equipment faces challenges such as long processing duration and low efficiency. Therefore, we investigated the impact of combining microbial agents with iron oxide nano-resin (Fe2O3@D201) on the aerobic degradation of FW. We conducted experiments using 10% microbial agents supplemented with 6% Fe2O3@D201 for FW degradation. Compared to the control group containing 10% microbial agents, the Fe2O3@D201-treated group showed higher levels of dissolved COD in the leachate, reaching 1.59 × 105 mg/L. Furthermore, the microbial hydrolytic enzyme activities in FW of this group surpassed those of the control group, with cellulase activity peaking at 0.13 U compared to the control group's peak of 0.06 U. Through 16S rRNA gene amplicon sequencing, we found that Fe2O3@D201 significantly enriched the abundance of Bacillus, which are commonly known for their hydrolysis functions. The results indicated that Fe2O3@D201 enhanced FW degradation by promoting the abundance of specialized microorganisms, and thus increased the hydrolytic enzyme activity, promoting the conversion of solid macromolecules into soluble organic matter. Consequently, Fe2O3@D201 shows potential for application in FW treatment equipment.

Electric field as an activator of inoculated Bacillus clausii enhances humification during electric field-assisted aerobic composting

A novel electric field-assisted aerobic composting (EAC) method effectively facilitates compost disposal by applying a low electric field to conventional aerobic composting (CAC). The humification effect of inoculation with Bacillus clausii in the EAC system was better than that in the CAC system, so this study focused on the enhancement effect of microbial inoculation in the EAC system. Compared with EAC, EAC with microbial inoculation (AMI-EAC) increased the degradation of cellulose, hemicellulose, and lignin. Furthermore, AMI-EAC improved the humification index by 42.89 % relative to EAC. AMI-EAC also increased the relative abundance of Bacillus, enriched thermophilic and electroactive microorganisms, and enhanced the activity of associated degradative enzymes, which promoted the decomposition and humification of organic matter. Partial least squares-path model analysis showed that Bacillus inoculation during AMI-EAC enhanced the direct positive effect of microorganisms on enzyme activity and strengthened the positive impacts of substance degradation and enzyme activity on compost maturation. This study provided new insights for inoculating microbial agents to enhance composting efficiency in future engineering applications of EAC.

Insights into nitrogen metabolism and humification process in aerobic composting facilitated by microbial inoculation

To enhance the retention of compost nutrients, specifically in nitrogen metabolism and humification, compound microbial agents were added during the aerobic composting of bagasse pith and buffalo manure. The introduction of the microbial agent successfully colonized the mixture, boosted the degradation capacity of organic matter, and facilitated the formation of nitrogenous substances and humic substances (HSs). The incorporation of a composite microbial inoculum led to a substantial rise in total Kjeldahl nitrogen (TKN) by 62.04%, nitrate nitrogen (NO- 3-N) by 291.65%, and amino acid (AA) by 78.77%. Furthermore, this intervention resulted in achieving a humic acid (HA) to fulvic acid (FA) ratio of 1.64. Metagenomic sequencing revealed enhanced synergistic interactions among microorganisms through inoculation, increasing the abundance of functional genes related to nitrification and nitrogen fixation compared to the uninoculated control. Spearman correlation analysis identified unclassified_c__Deltaproteobacteria, unclassified_f__Planctomycetaceae, Chryseosolibacter, unclassified_f__Hyphomicrobiaceae as the principal producers of HA. This research provides insights into the interactions between nitrogen metabolism and humification in composting, aiming to effectively retain compost nutrients and support the long-term sustainability of agriculture.

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.

Cattle manure composting driven by a microbial agent: A coupled mechanism involving microbial community succession and organic matter conversion

Aerobic composting has been used as a mainstream treatment technology for agricultural solid waste resourcing. In the present study, we investigated the effects and potential mechanisms of the addition of a microbial agent (LD) prepared by combining Bacillus subtilis, Bacillus paralicheniformis and Irpex lacteus in improving the efficiency of cattle manure composting. Our results showed that addition of 1.5 % LD significantly accelerated compost humification, i.e., the germination index and lignocellulose degradation rate of the final compost product reached values of 92.20 and 42.29 %, respectively. Metagenomic sequencing results showed that inoculation of cattle manure with LD increased the abundance of functional microorganisms. LD effectively promoted the production of humus precursors, which then underwent reactions through synergistic abiotic and biotic pathways to achieve compost humification. This research provides a theoretical basis for the study of microbial enhancement strategies and humus formation mechanisms in the composting of livestock manure.

Performance of co-composting Pholiota nameko spent mushroom substrate and pig manure at different proportions: Chemical properties and humification process

Co-composting is the controlled aerobic degradation of organics, using more than one feedstock. By combining the spent mushroom substrate of Pholiota nameko (SMS) and pig manure (PM), the benefits of each could be used to optimize the composting process and the final product. This study introduced a comprehensive evaluation strategy aimed at identifying the optimal co-composting ratio for these two substrates. A 120-day composting trial was conducted, blending SMS and PM in various ratios to evaluate the benefits of co-composting SMS-PM. The results indicated that dissolved organic matter (DOM) in SMS-derived compost primarily originated from plants, whereas PM-derived compost predominantly consisted of microbial metabolic products, and co-composting combined both sources. An increase in aromaticity and humification degree of DOM occurred during the composting process itself rather than being derived from autochthonous origin. Carbohydrates like phenols and alcohols broke down during composting, and microbes utilized polysaccharides as an energy source for humus formation. As co-composting progressed, the treatments with varying mass ratios of SMS to PM, including 8:2, 7:3, 6:4, 5:5, 4:6, and 3:7 were observed to result in a decline in aliphatic hydroxylated chains alongside an enhancement in aromaticity within the compost. Additionally, there was a conversion from organic carbon (C) to carboxyl C within humic acid (HA) due to oxidation and dehydrogenation processes that facilitated the formation of stable nitrogen-containing compounds characterized by condensed aromatic structures. Following thorough evaluation, it was determined that optimal composting efficacy occurred at a mass ratio of SMS to PM equal to 6:4. Post-compost analysis revealed increases in nutrient content; specifically, germination index (GI) value reached 132.7%, while organic matter content attained 45.3%. Conversely, electrical conductivity (EC), C contents of water-soluble substances and humin (Cwss and CHu) decreased by approximately 11.8%, 73.4%, and 29.8% respectively; meanwhile, C contents of humic-extracted acid and HA (CHE and CHA), along with degree of polymerization (DP), increased by 17.3%, 20.3% and 9.9% respectively. The proposed co-compost formula not only facilitated simultaneous recycling of both SMS and PM waste but also transformed them into high-quality organic fertilizers suitable for soil enrichment-effectively addressing challenges faced by both edible fungi cultivation and livestock industries while augmenting organic fertilizer sources for Black land protection.

Effect of thermophilic bacterial complex agents on synergistic humification of carbon and nitrogen during lignocellulose-rich kitchen waste composting

This work reported the effects of thermophilic bacterial agents on degrading persistent lignocellulose and reducing the loss of valuable nitrogen in kitchen waste (KW) composting. The results showed that thermophilic bacterial compound agents improved the high temperature period by 8 days, and increased the ligninase activity by 0.5-3 times during the composting process. The activity of cellulase increased up to 1 time in agent A (Geobacillus, Clostridium caenicola, Haloplasma) adding group by improving the microbial activity of lignocellulosic degradation metabolic pathways. Nitrogen storage increased to 70% in group added with agent B (Clostridium caenicola, Geobacillus, Clostridium sp. TG60-81) by increasing the population abundance of nitrogen-fixing microorganisms such as Bacillus, Hungateiclostridium and Herbaspirillum, and changed amino acid metabolic pathways. In general, agents A and B could increase the thermophilic phase, optimize the microbial community structure, realize the synergistic humification of carbon and nitrogen, and convert KW into mature and high quality fertilizers.

Combining citrus waste-derived function microbes with biochar promotes humus formation by enhancing lignocellulose degradation in citrus waste compost

The low degradation rate of lignocellulose limits the humification process of citrus organic waste composting. This study explored the roles of general microbial inoculation (GM), citrus waste-derived function microbial inoculation (CM), and CM combined with biochar (CMB) in citrus waste compost. Results showed microbial inoculations all promoted lignocellulose degradation and humus formation, but the roles of CM and CMB were better than GM, especially CMB. Compared to the control, CMB raised the temperature and duration of thermophilic phase by 2.8 °C and 4 days, and improved lignin degradation rate and humus content by 21.5% and 7.6%. Furthermore, CMB promoted bacterial community succession and cooperation, and decreased network complexity. Moreover, CMB strengthened the correlation between mainly bacterial communities and polysaccharides, reducing sugars as well as carbohydrates metabolic, enhancing the contribution of bacteria such as Bacillus, Flavobacterium and Staphylococcus to humus and its precursors. It concludes that the naturally derived microbes in compost had better effects on promoting humus synthesis than exogenous microbes, which provides a new route for rapid humification of high-lignin organic waste in composting.

The bioaugmentation effect of microbial inoculants on humic acid formation during co-composting of bagasse and cow manure

The effective degradation of recalcitrant lignocellulose has emerged as a bottleneck for the humification of compost, and strategies are required to improve the efficiency of bagasse composting. Bioaugmentation is a promising method for promoting compost maturation and improving the quality of final compost. In this study, the bioaugmentation effects of microbial inoculants on humic acid (HA) formation during lignocellulosic composting were explored. In the inoculated group, the maximum temperature was increased to 72.5 °C, and the phenol-protein condensation and Maillard humification pathways were enhanced, thus increasing the HA content by 43.85%. After inoculation, the intensity of the microbial community interactions increased, particularly for fungi (1.4-fold). Macrogenomic analysis revealed that inoculation enriched thermophilic bacteria and lignocellulose-degrading fungi and increased the activity of carbohydrate-active enzymes and related metabolic functions, which effectively disrupted the recalcitrant structure of lignocellulose to achieve a high humification degree. Spearman correlation analysis indicated that Stappia of the Proteobacteria phylum, Ilumatobacter of the Actinomycetes phylum, and eleven genera of Ascomycota were the main HA producers. This study provides new ideas for bagasse treatment and recycling and realizing the comprehensive use of resources.

Effectiveness of biological drying for citric acid dewatered sludge: Evaluating the impact of energy-efficient ventilation strategies

The effectiveness of dehydration and utilization processes for citric acid dewatered sludge is hampered by its high concentrations of polysaccharides, proteins, and water-binding properties of microbial extracellular polymers (EPS). This research explores the efficacy and mechanisms involved in extracting water from this type of sludge using biological drying technology, with varying rates of ventilation. Especially pertinent was the use of low ventilation rates as control variables. Our results suggest that a scheduled intermittent ventilation at lower rates allows for the most efficient removal of water, achieving a rate of 41.71 % within eight days, according to the zero-order kinetic model. Remarkably, the peak temperature registered was 60 °C, reaching this threshold in just 0.1 days and maintaining high temperatures for approximately 5.9 days. Component analysis of organic matter illustrated a preferential degradation process for lipids under these ventilation conditions which is pivotal for releasing and transforming bound water for efficient extraction, as well as facilitating the breakdown of easily hydrolysable materials. Further, polysaccharide/protein (EPS) decomposition contributed to water removal, though less significantly. The periodic ventilation strategy allowed for the maximum cumulative temperature to be sustained, demonstrating superior efficiency in harnessing bio-generated heat (82.77 % for water evaporation), resulting in dry sludge suitable for self-sustained combustion at relatively low cost ($26.61/t). Highlighted by this study is the considerable potential of energy-efficient ventilation methods in the biological drying treatment of citric acid fermented sludge and similar industrial waste materials.

The positive effect of the enzyme inducer (MnSO4) on the formation of humic substance in rice straw composting by stimulating key microorganisms

This study investigated the impact of adding enzyme inducer (MnSO4) on humic substance (HS) formation during straw composting. The results demonstrated that both enzyme inducer treatment group (Mn) and functional microorganism treatment group (F) led to an increase in the content of HS compared to the treatment group without enzyme inducer and functional microorganism (CK). Interestingly, the enzyme inducer exhibited a higher promoting effect on HS (57.80 % ~ 58.58 %) than functional microbial (46.54 %). This was because enzyme inducer stimulated the growth of key microorganisms and changed the interaction relationship between microorganisms. The structural equation model suggested that the enzyme inducer promoted the utilization of amino acids by the fungus and facilitated the conversion of precursors to humic substance components. These findings provided a direction for improving the quality of composting products from agricultural straw waste. It also provided theoretical support for adding MnSO4 to compost.

Effect evaluation of different green wastes on food waste digestate composting and improvement of operational conditions

This study attempted to determine the influence of diverse green wastes on food waste digestate composting and the improvement of operational conditions. Various effects of the green wastes (GW), with different types and sizes, initial substrate mixture C/N ratios, compost pile heights, and turning frequencies on the food waste digestate (FWD) composting were examined in the current work. The findings showed that the use of street sweeping green waste (SSGW) as an additive can maintain the thermophilic stage of the FWD composting for 28 days, while the end-product contained the greatest amounts of total phosphorus (TP, 2.29%) and total potassium (TK, 4.61%) and the lowest moisture content (14.8%). Crushed SSGW (20 mm) enabled the FWD composting to maintain the longest thermophilic period (28 days), achieving the highest temperature (70.2 °C) and seed germination index (GI, 100%). Adjusting the initial substrate mixture C/N ratio to 25, compost pile height to 30 cm, and turning frequency to three times a day could enhance the efficiency and improve the fertilizer quality of the co-composting of the FWD and SSGW. This study suggested that co-composting of FWD and SSGW (FWD/SSGW = 2.3, wet weight) is a promising technique for the treatment of municipal solid waste and provided significant theoretical data for the application of composting.

Enhancing humification and microbial interactions during co-composting of pig manure and wine grape pomace: The role of biochar and Fe2O3

Phenol-rich wine grape pomace (WGP) improves the conversion of pig manure (PM) into humic acid (HA) during composting. However, the impact of using combinations of Fe2O3 and biochar known to promote compost maturation remains uncertain. This research explored the individual and combined influence of biochar and Fe2O3 during the co-composting of PM and WGP. The findings revealed that Fe2O3 boosts microbial network symbiosis (3233 links), augments the HA yield to 3.38 by promoting polysaccharide C-O stretching, and improves the germination index to 124.82 %. Limited microbial interactions, increased by biochar, resulted in a lower HA yield (2.50). However, the combination weakened the stretching of aromatics and quinones, which contribute to the formation of HA, resulting in reduced the humification to 2.73. In addition, Bacillus and Actinomadura were identified as pivotal factors affecting HA content. This study highlights Fe2O3 and biochar's roles in phenol-rich compost humification, but combined use reduces efficacy.

Waste milk humification product can be used as a slow release nano-fertilizer

The demand for milk has increased globally, accompanied by an increase in waste milk. Here, we provide an artificial humification technology to recycle waste milk into an agricultural nano-fertilizer. We use KOH-activated persulfate to convert waste milk into fulvic-like acid and humic-like acid. We mix the product with attapulgite to obtain a slow-release nano fulvic-like acid fertilizer. We apply this nano-fertilizer to chickweeds growing in pots, resulting in improved yield and root elongation. These results indicate that waste milk could be recycled for agricultural purposes, however, this nano-fertilizer needs to be tested further in field experiments.

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.

Structural analysis of lignite-derived humic acid and its microscopic interactions with heavy metal ions in aqueous solution

Understanding heavy metal environmental behavior with humic acid (HA) is critical. There is currently a lack of information on the control of its structure organization on its reactivity to metals. The difference in HA structures under non-homogeneous conditions is critical for revealing its micro-interaction with heavy metals. The heterogeneity of HA was reduced using the fractionation method in this study, the chemical properties of HA fractions were analyzed using py-GC/MS, and the structural units of HA were proposed. Pb2+ was used as a probe to investigate the difference in the adsorption capacity of HA fractions. The microscopic interaction of structures with heavy metal was investigated and validated by structural units. The results show that as molecular weight increased, the oxygen content and the number of aliphatic chains decreased, but the opposite was true for aromatic and heterocyclic rings. The adsorption capacity for Pb2+ was as follows: HA-1 > HA-2 > HA-3. According to the linear analysis of the influencing factors of maximum adsorption capacity and possibility factors, the adsorption capacity was positively correlated with the contents of acid groups, carboxyl groups, phenolic hydroxyl groups, and the number of aliphatic chains. The phenolic hydroxyl group and the aliphatic-chain structure have the greatest impact. Therefore, structural differences and the number of active sites play an important role in adsorption. The binding energy of HA structural units to Pb2+ was calculated. It was found that the chain structure is easier to bind to heavy metals than aromatic rings, and the affinity of-COOH to Pb2+ is greater than that of -OH. These findings can help improve the adsorbent design.

Batch-fed composting of food waste: Microbial diversity characterization and removal of antibiotic resistance genes

The aim of this work was to study the impact of batch-fed strategies on bacterial communities and ARGs in compost. The findings demonstrate that batch-feeding helped maintain high temperatures in the compost pile for an extended period (above 50 °C for 18 days), which in turn facilitated water dissipation. High-throughput sequencing showed that Firmicutes played a significant role in batch-fed composting (BFC). They had a high relative abundance at the beginning (98.64%) and end (45.71%) of compost. Additionally, BFC showed promising results in removing ARGs, with reductions of 3.04-1.09 log copies/g for Aminoglycoside and 2.26-2.44 log copies/g for β_Lactamase. This study provides a comprehensive survey of BFC and demonstrates its potential for eliminating resistance contamination in compost.

Lignite drove phenol precursors to participate in the formation of humic acid during chicken manure composting

This study set out to explore the impact of lignite on preserving organic matter and promoting the formation of humic acid (HA) during chicken manure composting. Composting test was carried out for control (CK), 5 % lignite addition treatment (L1), 10 % addition treatment (L2) and 15 % addition treatment (L3). The results demonstrated that lignite addition effectively reduced the loss of organic matter. The HA content of all lignite-added groups was higher than that of CK, and the highest was 45.44 %. L1 and L2 increased the richness of bacterial community. Network analysis showed higher diversity of HA-associated bacteria in L2 and L3 treatments. Structural equation models revealed that reducing sugar and amino acid contributed to the formation of HA during CK and L1 composting, while polyphenol contributed more to the HA formation during L2 and L3 composting. Furthermore, lignite addition also could promote the direct effect of microorganisms on HA formation. Therefore, the addition of lignite had practical significance to enhance compost quality.

Addition of cellulose degrading bacterial agents promoting keystone fungal-mediated cellulose degradation during aerobic composting: Construction the complex co-degradation system

To excavate a complex co-degradation system for decomposing cellulose more efficiently, cellulose-degrading bacteria, including Bacillus subtilis WF-8, Bacillus licheniformis WF-11, Bacillus Cereus WS-1 and Streptomyces Nogalater WF-10 were added during maize straw and cattle manure aerobic composting. Bacillus and Streptomyces successfully colonized, which improve cellulose degrading ability. Continuous colonization of cellulose-degrading bacteria can promote the fungi to produce more precursors for humus and promote the negative correlation with Ascomycota. In the current study, the addition of cellulose-degrading bacteria has resulted in the rapid development of Mycothermus and Remersonia in the phylum Ascomycota as keystone fungal genera which constitute the foundation of the co-degradation system. Network analysis reveals the complex co-degradation system of efficient cellulose bacteria and mature fungi to treat cellulose in the process of straw aerobic composting mainly related to the influence of total carbon (TC) /total nitrogen (TN) and humic acid (HA)/fulvic acid (FA). This research offers a complex co-degradation system more efficiently to decompose cellulose aiming to maintain the long-term sustainability of agriculture.

Bioaugmentation on humification during co-composting of corn straw and biogas slurry

In order to increase the nutrients and humic acid (HA) contents of corn straw (CS) derived organic fertilizer and recover resources from biogas slurry (BS) simultaneously, the co-composting of CS and BS was carried out with the addition of biochar and microbial agents including lignocellulose degrading and ammonia assimilating bacteria. The results showed that 1 kg straw could treat 2.5 L BS by recovering nutrients and bio-heat introduced evaporation. The bioaugmentation strengthened both the polyphenol and Maillard humification pathways by promoting the polycondensation of precursors (reducing sugars, polyphenols, and amino acids). HA obtained in the microbial-enhanced group (20.83 g/kg), biochar-enhanced group (19.34 g/kg), and combined-enhanced group (21.66 g/kg) were significantly higher than that in the control group (16.26 g/kg). The bioaugmentation achieved directional humification and reduced the loss of C and N by promoting the CN formation of HA. The humified co-compost had nutrient slow-release effect in agricultural production.

Exogenous microbial antagonism affects the bioaugmentation of humus formation under different inoculation using Trichoderma reesei and Phanerochaete chrysosporium

This study was aimed at exploring the effect of antagonism of Trichoderma reesei (T.r) and Phanerochaete chrysosporium (P.c) on humification during fermentation of rice (RS) and canola straw (CS). Results showed that exogeneous fungi accelerated straw degradation and enzyme activities of CMCase, xylanase and LiP. P.c inhibited the activity of LiP when co-existing with T.r beginning, it promoted the degradation of lignin and further increased the production of humus-like substances (HLS) and humic-like acid (HLA) in later fermentation when nutrients were insufficient. The HLS of RTP was 54.9 g/kg RS, higher than the other treatments, and displayed more complex structure and higher thermostability. Brucella and Bacillus were the main HLA bacterial producers. P.c was the HLA fungal producer, while T.r assisted FLA and polyphenol transformation. Therefore, RTP was recommended to advance technologies converting crop straw into humus resources.

Current Trends in Bioaugmentation Tools for Bioremediation: A Critical Review of Advances and Knowledge Gaps

Bioaugmentation is widely used in soil bioremediation, wastewater treatment, and air biofiltration. The addition of microbial biomass to contaminated areas can considerably improve their biodegradation performance. Nevertheless, analyses of large data sets on the topic available in literature do not provide a comprehensive view of the mechanisms responsible for inoculum-assisted stimulation. On the one hand, there is no universal mechanism of bioaugmentation for a broad spectrum of environmental conditions, contaminants, and technology operation concepts. On the other hand, further analyses of bioaugmentation outcomes under laboratory conditions and in the field will strengthen the theoretical basis for a better prediction of bioremediation processes under certain conditions. This review focuses on the following aspects: (i) choosing the source of microorganisms and the isolation procedure; (ii) preparation of the inoculum, e.g., cultivation of single strains or consortia, adaptation; (iii) application of immobilised cells; (iv) application schemes for soil, water bodies, bioreactors, and hydroponics; and (v) microbial succession and biodiversity. Reviews of recent scientific papers dating mostly from 2022-2023, as well as our own long-term studies, are provided here.

Different Species of Epigeic and Anecic Earthworms Cause Similarly Effective and Beneficial Biocomposting—A Case Study Involving the Pernicious Aquatic Weed Salvinia (Salvinia molesta, Mitchell)

As reported recently by the present authors, vermicomposting by the epigeic earthworm Eisenia fetida transforms the highly ligninous and allelopathic aquatic weed salvinia (Salvinia molesta) into a benign organic fertilizer. The present study was carried out with four other earthworm species, including three epigeic species of different sizes and phytophagic habits: Eisenia andrei, Lumbricus rubillus, and Perionyx sansibaricus. One anecic species, with geophytophagous habits, was also explored for comparison: Drawida willsi. The objective was to see whether the type of salvinia transformation caused by E. fetida is a general phenomenon or whether there are significant differences in the nature of biocomposts generated by different earthworm species. Accordingly, the characteristics of the biocomposts separately generated by each of the six species mentioned above were assessed with UV-visible spectrophotometry, Fourier-transform infrared spectrometry, differential scanning calorimetry, thermogravimetry, and scanning electron microscopy. The studies reveal that, with minor variations, the biocomposting by all four species was able to remove the intransigence of salvinia and impart plant/soil-friendly attributes to it in substantial measures. All the findings obtained with different techniques corroborated each other in arriving at this conclusion. Hence, it can be said that, in general, biocomposting by earthworms takes away the toxicity of pernicious weeds such as salvinia, converting them into plant-friendly and soil-friendly biofertilizers.

Dissolved organic matter evolution can reflect the maturity of compost: Insight into common composting technology and material composition

Dissolved organic matter (DOM) can clearly reflect composting components changes, thus it is supposed to indicate the humification process during composting. To demonstrate this, three compost mixtures and two techniques were arranged. DOM evolution was detected by three spectral techniques. X-ray diffraction (XRD) showed that the crystal structure substances decreased gradually during the composting, including cellulose, struvite, sylvine, quartz, and calcite; Specifically, the struvite was found, which was conducive to the fixation of nitrogen and phosphorus. Fourier transform infrared spectroscopy (FTIR) and three-dimensional fluorescence spectroscopy (3D-EEM) further showed that pig manure-based mixtures, added cabbage, and windrow composting are beneficial to sugar, protein, fulvic acid, and soluble microbial by-products decompose and humic acids produce. This process was closely related to the change of physical-chemical parameters (temperature; pH; moisture content; and NH₄⁺-N content) and maturity index (C/N ratio, E₄/E₆ and GI). Therefore, DOM evolution could quickly reflect the maturity process of compost. In subsequent research, the quantitative analysis of DOM components can be considered to modify DOM spectral parameters, or to build a model, so as to achieve rapid evaluation of compost maturity.

Mechanism analysis of humification coupling metabolic pathways based on cow dung composting with ionic liquids

This study focused on how adding ionic liquids (IL) affects composting humification. During the warming and thermophilic phases, addition of IL increased precursors content, and increased the polymerization of humus (HS) at later stages. Furthermore, the final HS and humic acid (HA) content of experimental groups (T) groups 129.79 mg/g and 79.91 mg/g were higher than in control group (CK) 118.57 mg/g and 74.53 mg/g, respectively (p < 0.05). IL up-regulated the gene abundance of metabolism for carbohydrate and amino acid (AA), and promoted the contributions of Actinobacteria and Proteobacteria, which affected humification. The redundancy analysis (RDA) results showed that the citrate-cycle (TCA cycle)(ko0020), pentose phosphate pathway (ko00030), pyruvate metabolism (ko00620), glyoxylate and dicarboxylate metabolism (ko00630), propanoate metabolism (ko00640), butanoate metabolism (ko00650) positively correlated with HA and HI. HA and humification index (HI) positively correlated with AA metabolic pathways, and fulvic acid (FA) was negatively correlated with these pathways. Overall, metabolism for carbohydrate and AA metabolism favored compost humification. ILs improved metabolism for carbohydrate and amino acid metabolism, thus enhancing humification.

Two novel phosphorus/potassium-degradation bacteria: Bacillus aerophilus SD-1/Bacillus altitudinis SD-3 and their application in two-stage composting of corncob residue

For effective utilization of corncob residue to realize green circular production, using composting to obtain a high-quality and low-cost biomass fertilizer has become a very important transformation avenue. In this paper, two novel phosphorus/potassium-degradation bacterial strains were isolated from tobacco straw and identified as Bacillus aerophilus SD-1/Bacillus altitudinis SD-3 (abbreviated as SD-1/SD-3). These identified two novel bacteria SD-1/SD-3 show that the soluble phosphorus content of SD-1/SD-3 reached 360.89 mg L^-1/403.56 mg L^-1 in the shake flask test, and the mass concentration of soluble potassium is 136.56 mg L^-1/139.89 mg L^-1. In addition, the Laccase (Lac), Lignin peroxidase (LiP), and Manganese peroxidase (MnP) activities of SD-1 and SD-3 are 54.45 U L^-1/394.84 U L^-1/222.79 U L^-1 and 46.27 U L^-1/395.26 U L^-1/203.98 U L^-1 respectively, with the carboxy-methyl cellulase (CMCase) of 72.07 U mL^-1 and 52.69 U mL^-1. Meanwhile, the effects of three different combinations of cultures, i.e., no inoculation (K1), inoculation of SD-1/SD-3 on day 21 (K2) and on day 0 (G) are investigated to understand the influence on the degradation degree of corncob residue compost. The results of K2 compost treatment showed that the effective P/K content increased nearly 3.1/2.4 times, the degradation of cellulose/lignin was 49.1/68.0%, and the germination rate was 110.23%, which were higher than other experiment groups K1/G. In conclusion, knowledge of this paper will be very useful for the industrial sector for the treatment of complex corncob residue.

Independent and combined effects of biochar and microbial agents on physicochemical parameters and microbial community succession during food waste composting

This study evaluated the independent and combined effects of biochar and microbial agents on food waste composting. The results indicated that combined addition increased the peak temperature to 63.5 °C and extended the thermophilic periods to 8 days, resulting in the highest organic matter degradation rate (12.7%). Analysis of enzymatic activity indicated that combined addition increased urease and dehydrogenase activity by 22.9% and 26.5%. Furthermore, the degradation of volatile fatty acids also increased by 37.4% with combined addition. Microbial analysis demonstrated that combined addition effectively increased the relative abundances of Enterobacter, Sphingobacterium and Aspergillus, which could be attributed to the optimal environment provided by biochar and stimulation of microbial agents. Moreover, correlation analysis showed a strong interaction between the microbial community and environment with combined addition. In general, combined addition could be beneficial for composting based on the synergistic effects of biochar and inoculation on microorganism.

Phytotoxicity of farm livestock manures in facultative heap composting using the seed germination index as indicator

Static facultative heap composting of animal manure is widely used in China, but there is almost no systematic research on the phytotoxicity of the produced compost. Here, we evaluated the phytotoxic variation in compost produced by facultative heap composting of four types of animal manure (chicken manure, pig manure, sheep manure, and cattle manure) using different plant seeds (cucumber, radish, Chinese cabbage, and oilseed rape) to determine germination index (GI). The key factors that affected GI values were identified, including the dynamics of the phytotoxicity and microbial community during heap composting. Sensitivity to toxicity differed depending on the type of plant seed used. Phytotoxicity during facultative heap composting, evaluated by the GI, was in the order: chicken manure (0-6.6 %) < pig manure (14.4-90.5 %) < sheep manure (46.0-93.0 %) < cattle manure (50.2-105.8 %). Network analysis showed that the volatile fatty acid (VFA) concentration was positively correlated with Firmicutes abundance, and NH₄⁺-N was correlated with Actinobacteria, Proteobacteria, and Bacteroidetes. More bacteria were stimulated to participate in conversions of dissolved organic carbon, dissolved nitrogen, VFA, and ammonia-nitrogen (NH₄⁺-N) in sheep manure heap composting than that in other manure. The GI was most affected by VFA in chicken manure and cattle manure heap composting, while NH₄⁺-N was the main factor affecting the GI in pig manure and sheep manure compost. The dissolved carbon and nitrogen content and composition, as well as the core and proprietary microbial communities, were the primary factors that affected the succession of phytotoxic substances in facultative heap composting, which in turn affected GI values. In this study, the key pathways of livestock manure composting that affected GI and phytotoxicity were found and evaluated, which provided new insights and theoretical support for the safe use of organic fertilizer.

Evaluating differences in humic substances formation based on the shikimic acid pathway during different materials composting

This study aimed to evaluate differences in humic substance (HS) formation based on the shikimic acid pathway (SAP) during five different materials composting. The results showed that compared with other three materials, gallic acid, protocatechuic acid and shikimic acid of the SAP products in lawn waste (LW) and garden waste (GW) compost decreased significantly. Furthermore, as important indicators for evaluating humification, humic acid and degree of polymerization increased by 39.4%, 79.5% and 21.8%, 87.9% in LW and GW, respectively. Correlation analysis showed that SAP products were strongly correlated with HS fractions in LW and GW. Meanwhile, network analysis indicated that more core bacteria associated with both SAP products and HS were identified in LW and GW. Finally, the structural equation model proved that SAP had more significant contribution to humification improvement in LW and GW. These findings provided theoretical foundation and feasible actions to improve compost quality by the SAP.

The neglected effects of polysaccharide transformation on sludge humification during anaerobic digestion with thermal hydrolysis pretreatment

Humus accumulation during sludge stabilization is attracting increasing attention because of its land use potential. This study investigated the effects of thermal hydrolysis pretreatment (THP) on sludge humification and the related regulatory mechanisms during anaerobic digestion (AD). The sludge subjected to AD with THP at 160 °C (AnD-160) exhibited 7.3% and 8.5% higher total extractable carbon (TEC) and humic acid carbon (HAC) concentrations than the unpretreated sludge, respectively, while the sludge subjected to AD with THP at 180 °C (AnD-180) exhibited 1.4% and 7.0% lower concentrations. Humification of AnD-160 and AnD-180 were enhanced and inhibited, respectively. THP influenced sludge humification during AD through both intracellular polyphenol synthesis and extracellular humus condensation pathways related to polysaccharide metabolism. The 160 °C-pretreated sludge exhibited higher polysaccharide availability (more soluble polysaccharides and reducing sugars) than the other samples and thus had more active intracellular polyphenol metabolism during AD. The polyphenol accumulation stimulated the synthesis of related condensation enzymes (polyphenol oxidase and quinone oxidoreductases), facilitating extracellular HA production during AD. However, THP at 180 °C resulted in the highest production of melanoidins with CO-C heterocycles through C = O and CH sites of polysaccharides (778.46 vs. 193.87 R.U. nm²-mL/g for the unpretreated sample). This heterocyclization decreased the polysaccharide availability and inhibited intracellular polyphenol synthesis, consequently inhibiting condensation enzymes supply and extracellular HA production during AD. Overall, this study highlights the crucial but neglected role of polysaccharides in sludge humification during AD: the availability of polysaccharides affected by their occurrence state and molecular structure could determine the humification, which can be regulated by THP at different temperature.

Metagenomics analysis revealed the coupling of lignin degradation with humus formation mediated via shell powder during composting

This study was the first to explore the effect of shell powder (SP) on lignin degradation and humus (HS) formation during composting. The results showed that the treatment group (T) with SP consumed more polyphenols, reducing sugar and amino acids than the control group (CK), especially the rate of reducing sugar consumption in T (50.61 %) was significantly higher than CK (28.40 %). SP greatly enhanced the efficiency of lignin degradation (T:45.47 %; CK:24.63 %) and HS formation (T:34.93 %; CK:20.16 %). The content of HA in T was 12.94 mg/g while CK was 12.06 mg/g. SP maintained a continuous increase in the relative abundance of AA1, AA3 after cooling phase. Meanwhile, T (48.98 %) significantly increased the abundance of Actinobacteria compared with CK (37.19 %). Actinobacteria, AA1 and AA3 were identified as the main factors promoting lignin degradation and HS formation by correlation analysis. Therefore, adding SP could be a novel strategy to improve compost quality.

Exolaccase-boosted humification for agricultural applications

Globally, phenolic contaminants have posed a considerable threat to agro-ecosystems. Exolaccase-boosted humification may be an admirable strategy for phenolic detoxification by creating multifunctional humic-like products (H-LPs). Nonetheless, the potential applicability of the formed H-LPs in agricultural production is still overlooked. This review describes immobilized exolaccase-enabled humification in eliminating phenolic pollutants and producing artificial H-LPs. The similarities and differences between artificial H-LPs and natural humic substances (HSs) in chemical properties are compared. In particular, the agronomic effects of these reproducible artificial H-LPs are highlighted. On the basis of the above summary, the granulation process is employed to prepare granular humic-like organic fertilizers, which can be applied to field crops by mechanical side-deep fertilization. Finally, the challenges and perspectives of exolaccase-boosted humification for practical applications are also discussed. This review is a first step toward a more profound understanding of phenolic detoxification, soil improvement, and agricultural production by exolaccase-boosted humification.

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Exolaccase-initiated humification is conductive to phenolic detoxification

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Multiple humic-like products are created in exolaccase-boosted humification

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Similarities and differences between artificial and natural humus are disclosed

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Humic-like products can be used to sustain soil health and increase crop yield