Improving the humification by additives during composting: A review

Alternating electric field as an effective inhibitor of bioavailability and phytotoxicity of heavy metals during electric field-assisted aerobic composting

Changing the form of the electric field in the electric field-assisted aerobic composting (EAC) system from direct current to alternating current is confirmed as a potential strategy to enhance compost humification to the level of hyperthermophilic composting. This study pioneered the comparative evaluation of the effects of different electric field forms on the immobilization and phytotoxicity of heavy metals during composting. The results demonstrated that the humic acid content and humification index of alternating electric field-assisted aerobic composting (AEFAC) were approximately 22.0 % and 33.7 % higher than that of EAC, respectively. Morphometric analysis of various HMs (Cu, Zn, Cr, Cd, and Pb) revealed that the amounts in the exchangeable and reducible fractions were obviously lower in AEFAC than in EAC. AEFAC reduced the bioavailability of multiple HMs to about 15.11-40.21 %, indicating the higher passivation efficiency of several HMs than EAC. PLS-PM analysis indicated that AEFAC inhibited HMs bioavailability mainly through physicochemical properties, humification parameters, and microbial communities. Phytotoxicity experiments confirmed that AEFAC improves the growth indicators of cultivated crops, resulting in a 26.2 % increase in plant height and a 36.2 % increase in root length compared to EAC. Moreover, compared with EAC, AEFAC reduces the accumulation of Cu, Zn, Cr, Cd, and Pb in cultivated plants by approximately 27.0 %, 30.9 %, 32.2 %, 8.6 %, and 10.9 %, respectively. This study provides the first proof of principle that AEFAC effectively promotes the passivation of HMs, providing a practical strategy for efficient and environmentally friendly compost disposal.

Decreased particle size enhances the aging behavior of microplastics during sewage sludge composting: Physicochemical properties and cadmium loading

Although aerobic composting is capable of aging microplastics (MPs), the influence of size on MPs aging during composting and loading of cadmium (Cd) remains unclear. Therefore, we investigated variations in the physicochemical properties of polyethylene terephthalate microplastics (PET-MPs) with different sizes (1.0 -5.0, 0.2 -1.0, and 0.05 -0.2 mm) during composting and the concentration of Cd accumulated on the surface of different-sized aged PET-MPs. The results indicated that PET-MPs exhibited size-dependent as they aged during composting, with smaller sizes aging faster. After composting, the 0.05 -0.2 mm PET-MPs had the greatest increase in specific surface area (205.5 %), compared with the 1.0 -5.0 mm (18.7 %) and 0.2 -1.0 mm (95.6 %) PET-MPs. The greatest increase in the carbonyl index/oxygen-to-carbon atom ratio was also observed for the 0.05 -0.2 mm PET-MPs, which were 2.25 / 3.27 and 0.02 / 2.11 times higher than those of the 1.0 -5.0 mm and 0.2-1.0 mm PET-MPs, respectively. Similarly, size-dependent accumulation of Cd on the aged PET-MPs was also observed: 0.05-0.2 mm (5.37 mg/kg Cd) > 0.2 -1.0 mm (2.90 mg/kg Cd) > 1.0-5.0 mm (0.78 mg/kg Cd). These findings demonstrate that the aging behavior of polymer is closely related to their size, emphasizing the role of size in the fate and pollutant loading of polymer.

Biochar and pyroligneous acid contributed to the sustainable reduction of ammonia emissions: From compost process to soil application

Aerobic composting is vital for resource recycling but struggles with high ammonia (NH3) emissions. Biochar (BC) and pyroligneous acid (PA), products of waste pyrolysis, have great potential for reducing NH3 emissions. However, the effective utilization of BC and PA to reduce NH3 emissions in both compost process and product application remains unclear. In this study, different amounts of BC and PA were incorporated into the composting process. The evaluation indexes of compost products were systematically assessed and compared through the cultivation of amaranth. Results demonstrated that rational use of BC and PA could enhance compost quality and effectively reduce NH3 emissions. The addition of 15 %BC+ 3 %PA resulted in a 92.31 % increase in NH4+-N content while reducing NH3 emission by 39.94 % during composting. The synergistic effect achieved by maintaining NH4+-N, enhancing NO3--N, and regulating pH. The compost products in 15 %BC+ 3 %PA complied with the requirements of China's National organic fertilizer standard. Moreover, these compost products demonstrated soil sustained fertility effects, reducing NH3 emission by 41.05 %-69.66 % and increasing total weight of amaranth by 4.62 % by a dosage of 4 %. This study is highly significant for addressing the issue of NH3 emission in both the compost process and soil application.

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.

Phosphate-coupled high-carbon ferromanganese particles synergistically regulate co-composting of seaweed and corn starch residue: Improving nitrogen cycling and accelerating humification

A substantial amount of seaweed waste, rich in plant-stimulating properties, holds great potential for composting. However, without proper catalysts or additives, composting and humification are slow and inefficient, causing carbon and nitrogen losses. This study explores a novel approach to enhance composting efficacy by coupling phosphate with high-carbon ferromanganese particles (HCFMP). The results indicate that the phosphate-HCFMP coupling promotes humus precursor transformation, as evidenced by dynamic changes in reducing sugars, amino acids, and polyphenols. Additionally, ultraviolet characteristic parameters and Parallel Factor (PARAFAC) analysis show that the coupled treatment improves both the rate and degree of humification. By the end of composting, this treatment exhibited the highest HA/FA (4.38), with the HA/FA on day 21 surpassing other treatments on day 35. While the phosphate-only group achieved a relatively high degree of humification, the process was slower and accompanied by substantial NH3 volatilization. The HCFMP-only group reduced NH3 emissions, but the oxidative performance of HCFMP was enhanced under lower pH conditions, reducing organic matter participation in humus formation. Compared to phosphate alone, the coupled treatment reduced NH3 emissions by 48.6% and increased nitrate content by 12%. Further analysis suggests that the enhancement mechanisms may include: (1) phosphate stimulating humus precursor production; (2) HCFMP mainly acting as a catalyst under higher pH to promote precursor polymerization; and (3) HCFMP's acidic sites adsorbing NH3/NH4+ and facilitating nitrification. In conclusion, coupling HCFMP with phosphate enhances composting efficacy, and the resulting products, with plant-stimulating properties, offer a feasible solution for sustainable green agriculture development.

Microbial augmented aerobic composting for effective phthalates degradation in activated sludge

Phthalate esters (PAEs) accumulated in activated sludge posed serious threats to agroecosystems and environment. Traditional aerobic (AE) and anaerobic (AN) composting were limited in achieving sustained PAEs degradation due to the single structure of microbial community. Here, the effectiveness and microbiological mechanisms of bacterial-augmented aerobic composting (AEB) in reducing activated sludge PAEs were investigated, with comparison of anaerobic composting (ANB). Results showed that AEB treatments significantly enhanced PAEs degradation efficiency through batch degradation experiments and microbial community analysis. At initial PAEs contamination levels of 50 mg/kg and 100 mg/kg, di-n-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) removal rates increased by 2.11-3.93-fold and 2.18-3.36-fold, respectively. Notably, AEB treatment reshaped bacterial community structure, forming communities dominated by efficient PAEs-degrading bacteria. Network analysis revealed a more complex microbial interaction networks under AE treatment, with the numbers of node and connectivity being 1.5 and 1.8 times than that of AN treatment. Functional gene prediction indicated increased abundances of PAEs degradation-related functional groups. Environmental factor analysis demonstrated optimized conditions through pH control, oxygen supply, and active carbon-nitrogen metabolism. These findings provided important supports for safe activated sludge disposal and resource utilization.

Machine learning-based prediction of compost maturity and identification of key parameters during manure composting

Evaluating compost maturity, e.g. via manual seed germination index (GI) measurement, is both time-consuming and costly during composting. This study employed six machine learning methods, including random forest (RF), extra tree (ET), eXtreme gradient boosting, gradient boosting decision tree, back propagation neural network, and multilayer perceptron, to develop models for predicting GI during manure composting. RF and ET exhibited robust predictive performance for GI, achieving high coefficient of determination (R2) of 0.937 and 0.904, respectively, along with root mean squared error of 7.261 and 8.930. SHapley additive exPlanations identified the duration time of composting, total nitrogen, and electrical conductivity as the key features influencing GI. Validation with actual GI data further confirmed the effectiveness of RF and ET models in predicting GI. This study could facilitate optimizing manure composting strategies, enable efficient parameter regulation, reduce labor costs, assist in anomaly detection, and promote intelligent management in real-world composting practices.

Harnessing the potential of exogenous microbial agents: a comprehensive review on enhancing lignocellulose degradation in agricultural waste composting

Composting converts organic agricultural wastes into value-added products, yet the presence of significant non-biodegradable lignocelluloses hinders its efficiency. The introduction of various exogenous microbial agents has been shown to effectively addresses this challenge. In this context, basing on the microbial enzymatic mechanism for lignocellulose degradation, this paper synthesizes the latest research advancements and practical applications of exogenous microbial agents in agricultural waste composting. Given that the effectiveness of lignocellulose degradation is highly dependent on the waste's inherent characteristics, it is crucial to carefully consider the composition of fungi and bacteria, the dosage of microbial agents, and the composting process operation, tailored to the specific type of agricultural waste. Moreover, the combination of additives with exogenous microbial agents can further enhance the degradation of lignocelluloses and the humification of organic matters. Furthermore, insights into the future research and application trends of exogenous microbial agents in agricultural waste composting was prospected.

The impact of the structural transformation mechanism of fulvic acid on redox capacity during composting with different biowastes

Fulvic acid (FA) derived from composting functions can act as electron shuttle, facilitating and expediting the redox reaction during the composting process. However, limited research has been conducted on the redox capacity and structural transformation of FA during composting with different biowastes. The Fe (II) production quantity of the single S. oneidensis MR-1 (MR-1), MR-1 with FA derived from lignocellulose-rich and lignin-rich composting after 300 h inoculation were up to 2.28, 3.67 and 2.52 mmol/L, indicating the redox capacity of FA in lignocellulose-rich composts was stronger than that in lignin-rich composting. Furthermore, two-dimensional correlation spectroscopy revealed that FA derived from lignocellulose-rich composting exhibited a layer-by-layer structure, characterized by aromatic functional groups and other groups. In contrast, FA obtained from lignin-rich composting displayed an arrangement where the inner aromatic functional groups were obstructed by the methyl group. The structural equation model revealed that the high relative abundance and aromatic functional groups of FA derived from lignocellulose-rich composting process exert a direct influence on the reduction of Fe (III)-citrate, and the methyl groups of FA obtained from lignin-rich composting process also directly linked to the reduction of Fe (III)-citrate. The present study thus posited that the quantity of aromatic functional groups within outer of FA structure during composting constituted a crucial factor influencing its redox capacity. The findings offer novel insights into the transformation mechanism of FA derives from diverse biowastes and its redox characteristics, thereby providing significant guidance for the application of FA in mitigating environment pollutants.

Unraveling the mechanisms of post-treatment to enhance humification and Cd remediation in compost through EDTA-Fenton-Like systems

This study aimed to enhance humification and cadmium (Cd) remediation in compost by investigating the effects of three post-treatments: ultrapure water, citric acid, and ethylenediaminetetraacetic acid disodium (EDTA). The results revealed that the EDTA post-treatment significantly enhanced humification by facilitating an EDTA-Fenton-like system within compost comprising rice straw and river sediment to remediate Cd-contaminated sediment. EDTA post-treatment not only promoted humic substances and humic acid concentrations of up to 66.30 g/kg and 30.40 g/kg, respectively, but also led to a reduction in the Cd content and bioavailability factor by 75.02 % and 9.76 %, respectively. In addition, parallel factor analysis revealed two distinct components, while two-dimensional correlation spectroscopy showed that the polysaccharides and carboxyl groups in humic acid were preferentially bound to Cd. Overall, this study proposes a promising approach for enhancing humification and Cd remediation in compost by the EDTA post-treatment.

Synergistic effects of heterogeneous mature compost and aeration rate on humification and nitrogen fixing during kitchen waste composting

Sludge mature compost (SMC) is notable for its high production, easy accessibility, and stable supply. This study investigated the impact of the SMC addition and different aeration rates on the humification and nitrogen fixing process during kitchen waste composting. The results demonstrated that addition of SMC prolonged the thermophilic phase, as a comparison, increased aeration shortened this phase. The addition of SMC and increased aeration enhanced humus formation and nitrogen retention. SMC introduced more amide and polysaccharide compounds into the compost, promoting the Maillard humification pathway. Additionally, both SMC and high aeration inhibited denitrification: the SMC reduced the abundance of the nirK gene, while high aeration decreased the abundance of nosZ gene. Network analysis revealed that higher aeration enhanced fungal interactions but diminished bacterial interactions. Conversely, SMC addition bolstered both bacterial and fungal interactions. The final compost product with SMC addition showed a 11.56%-44.19% reduction in antibiotic resistance gene content compared with the control group, and heavy metal contents remained within safe application limits. The combination of high SMC addition and high aeration achieved optimal humification and nitrogen retention, underscoring its potential as a promising solution for kitchen waste composting.

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.

Recycled calcium polypeptides modulate microbial dynamics and enhance bioconversion in kitchen waste-garden waste co-composting system

The kitchen waste and garden waste (KW-GW) co-composting system provides an effective method for recycling these two types of municipal solid waste; however, further improvements are needed to enhance bioconversion performance. This study investigates a novel composting additive, calcium polypeptides (CPPs), derived from waste animal and plant proteins, which can enhance the bioconversion capacity of biomass in the KW-GW co-composting system. As a pH regulator and an available nitrogen source, CPPs significantly increase the compost matrix pH, prolong the thermophilic phase, and reduce emissions of exhaust gases such as CH4, N2O, NH3, and H2S by 52.5%, 37.9%, 17.5%, and 41.3%, respectively. Moreover, the addition of CPPs to the compost product resulted in a 32.6% increase in humic substance content, while the germination index reached 108.5%, significantly promoting the growth of ryegrass. Microbial diversity analysis revealed that CPPs significantly altered microbial richness and diversity in the KW-GW co-composting system. During the heating phase, CPPs positively correlated with the abundance of thermophilic and lignocellulose-degrading species, such as Bacillus, Corynebacterium, and Aspergillus, along with composting temperature, pH, and electrical conductivity. Conversely, CPPs negatively correlated with the abundance of acidogenic and methanogenic species like Lactobacillus, Streptococcus, and Weissella. In the maturation phase, CPPs positively correlated with the abundance of lignocellulose-degrading and humus-forming species, including Pseudoxanthomonas, Sphingobacterium, and Aspergillus, as well as with the germination index. These results indicate that recycled CPPs improve the microenvironment, boosting biomass conversion in the KW-GW co-composting system, providing a viable approach for resourceful waste biomass reuse.

Unraveling the impact of intervention strategies and oxygen disparity in humification during domestic waste composting

This study constructs three different photovoltaic assisted composting systems to treat rural domestic waste, and explores the interaction pathways between biomacromolecules and other factors under oxygen disparity at gradient heights of the compost. The optimized mode of regular turning and ventilation-dehydration significantly reduced the moisture content by 53.6% and increased the seed germination index by 35.6%. The oxygen content at different heights under the optimized mode significantly affects the physicochemical properties of the compost, and the degradation of cellulose, hemicellulose, and protein in the middle is higher than other parts. The structural equation model shows that the physicochemical properties at the bottom are affected by biomacromolecules, which may be related to volatile fatty acids(VFAs) produced under low oxygen conditions.The research results show that using manual turning and ventilation-dehydration as the optimized process can promote compost maturity, and oxygen concentration has an important impact on the humification process of the compost.

Improved humification and Cr(VI) immobilization by CaO2 and Fe3O4 during composting

The current research studied how Fe3O4 nanomaterials (NMs) and CaO2 affect humification and Cr(VI) immobilization and reduction during the composting of oil-tea Camellia meal and Cr-contaminated soil. The results showed that Fe3O4 NMs and CaO2 successfully construct a Fenton-like reaction in this system. The excitation-emission matrix-parallel factor (EEM-PARAFAC) demonstrated that this Fenton-like treatment increased the generation of humic acids and accelerated the humification. Meantime, RES-Cr increased by 5.91 % and Cr(VI) decreased by 16.36 % in the treatment group with CaO2 and Fe3O4 NMs after 60 days. Moreover, the microbial results showed that Fe3O4 NMs and CaO2 could promote the enrichment of Cr(VI) reducing bacteria, e.g., Bacillus, Pseudomonas, and Psychrobacter, and promote Cr(VI) reduction. This study gives a novel view and theoretical reference to remediate Cr(VI) pollution through 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.

Potassium persulfate enhances humification of chicken manure and straw composting: The perspective of rare and abundant microbial community structure and ecological interactions

Improper disposal of organic solid waste results in serious environmental pollution. Aerobic composting provides an environmentally friendly treatment method, but improving humification of raw materials remains a challenge. This study revealed the effect of different concentrations of potassium persulfate (PP) on humification of chicken manure and straw aerobic composting and the underlying microbial mechanisms. The results showed that when 0.6 % PP was added (PPH group), humus and the degree of polymerization were 80.77 mg/g and 2.52, respectively, which were significantly higher than those in 0.3 % PP (PPL group). As the concentration of PP was increased, the composition of rare taxa (RT) changed and improved in evenness, while abundant taxa (AT) was unaffected. Additionally, the density (0.037), edges (3278), and average degree (15.21) in the co-occurrence network decreased compared to PPL, while the average path (4.021) and modularity increased in PPH. This resulted in facilitating the turnover of matter, information, and energy among the microbes. Interestingly, cooperative behavior between microorganisms during the maturation period (24-60 d) occurred in PPH, but competitive relationships dominated in PPL. Cooperative behavior was positively correlated with humus (p < 0.05). Because the indices, such as higher degree, betweenness centrality, eigenvector centrality, and closeness centrality of the AT, were located in the microbial network center compared to RT, they were unaffected by the concentration of PP. The abundance of carbohydrate and amino acid metabolic pathways, which play an important role in humification, were higher in PPH. These findings contribute to understanding the relative importance of composition, interactions, and metabolic functionality of RT and AT on humification during chicken manure and straw aerobic composting under different concentrations of PP, as well as provide a basic reference for use of various conditioning agents to promote humification of organic solid waste.

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.

Enhancing compost quality through biochar and oyster shell amendments in the co-composting of seaweed and sugar residue

Aquaculture and agricultural production generate substantial amounts of waste, including seaweed (which has plant-stimulating properties), oyster shells, and sugar residues. Through composting and appropriate management, these wastes have the potential to be converted into beneficial soil amendments. However, there is a lack of research exploring the potential of composting in promoting the conversion of seaweed into more stable humified forms, as well as in assessing whether composted seaweed retains its beneficial effects on plant growth. Additionally, studies on using oyster shells as additives to reduce waste pressure and comparing their effectiveness with biochar are relatively scarce. This study examines the impact of incorporating 5% corn stover biochar (T1), 10% biochar (T2), and 10% oyster shell powder (T3) on key physicochemical properties, product quality, and microbial community dynamics during the co-composting of seaweed and sugar residues. Results indicate that organic matter (OM) loss in T1 and T2 increased by 31.2% and 26.4%, respectively, compared to the control (CK). Moreover, Excitation-emission matrix (EEM) fluorescence spectroscopy revealed that humic substances in T1 and T2 surged by 434% and 423%, respectively, far exceeding the 289% increase in CK. The 10% biochar treatment also improved alginate degradation and seed germination index, due to the presence of biostimulants in seaweed and an increased abundance of Cobetia. Microbial analysis post-composting showed that T2 and T3 significantly enhanced the diversity and richness of bacterial communities. Notably, although oyster shell powder did not improve the humification degree of compost as significantly as biochar, it achieved effective weight reduction of waste (OM loss of 43.57%, far exceeding CK's 35.34%) without hindering the composting process. All four compost treatments retained the plant-stimulating effects of seaweed and facilitated alginate degradation. These results underscore the potential of biochar to enhance composting efficiency and utilize composting to process large quantities of oyster shell waste.

Revealing mechanism of phenol-amine reaction to form humus in compost based on high-resolution liquid chromatography mass spectrometry and spectroscopy

Humus is the stable form of carbon storage in straw compost. The phenol-amine reaction is a pathway for humus formation in straw compost. In this study, two reaction systems, GP group (pyrogallol and glycine) and GCP group (catechol, pyrogallol, and glycine), were constructed in a simulated composting environment and revealed the molecular binding mechanism of the phenol-amine reaction through spectroscopy and mass spectrometry. The results showed that phenolic self-polymerization was faster than phenol-amine reaction. Therefore, the aromatization degree of GP was 27.14 % higher than that of GCP. The phenol-amine reaction first produced fulvic acid, and then formed humus units rich in active functional group structures (i.e., phenolic hydroxyl and carboxyl groups). These units further captured small molecule compounds to form humic acid eventually. This study would provide theoretical support for exploring the humus formation process and the promotion of straw humification by adding phenol or amino acids to compost.

Modifying humus-phosphorus-arsenic interactions in sludge composting: The strengthening of phosphorus availability and arsenic efflux detoxification mechanisms

Arsenic (As) in sewage sludge poses a significant threat to environmental and human health, which has attracted widespread attention. This study investigated the value of adding sodium percarbonate (SP) on phosphorus (P) availability and As efflux detoxification through HS-P-As interactions. Due to the unique structure of humus (HS) and the similar chemical properties of P and As, the conditions for HS-P-As interaction are provided. This study discussed the content, morphology and microbial communities of HS, P and As by using metagenomic and correlation analysis. The results showed that the humification index in the experiment group (SPC) was 2.34 times higher than that in the control group (CK). The available phosphorus (AP) content of SPC increased from 71.09 mg/kg to 126.14 mg/kg, and SPC was 1.11 times that of CK. The relative abundance of ACR3/ArsB increased. Pst, Actinomyces and Bacillus commonly participated in P and As conversion. The correlation analysis revealed that the humification process was enhanced, the AP was strengthened, and the As was efflux detoxified after SP amendment. All in all, this study elucidated the key mechanism of HS-P-As interaction and put forward a new strategy for sewage sludge resource utilization and detoxification.

The effects of different electrode materials on the electric field-assisted co-composting system for the soil remediation of heavy metal pollution

The electric field-assisted composting system (EACS) is an emerging technology that can enhance composting efficiency, but little attention has been given to electrode materials. Herein, an EACS was established to investigate the effects of electrode materials on humic substance formation and heavy metal speciation. Excitation-emission matrix analysis showed that carbon-felt and stainless-steel electrodes increased humic acid (HA) by 48.57 % and 47.53 %, respectively. In the EACS with the carbon-felt electrode, the bioavailability factors (BF) of Cu and Cr decreased by 18.00 % and 7.61 %, respectively. Despite that the stainless-steel electrodes decreased the BF of As by 11.26 %, the leaching of Cr, Ni, Cu, and Fe from the electrode itself is an inevitable concern. Microbial community analyses indicated that the electric field increased the abundance of Actinobacteria and stimulated the multiplication of heavy metal-tolerant bacteria. Redundancy analysis indicates that OM, pH, and current significantly affect the evolution of heavy metal speciation in the EACS. This study first evaluated the metal leaching risk of stainless-steel electrode, and confirmed that carbon-felt electrode is environment-friendly material with high performance and low risk in future research with EACS.

Changes in the Glucose Concentration Affect the Formation of Humic-like Substances in Polyphenol-Maillard Reactions Involving Gibbsite

The polyphenol-Maillard reaction is considered one of the important pathways in the formation of humic-like substances (HLSs). Glucose serves as a microbial energy source that drives the humification process. However, the effects of changes in glucose, particularly its concentration, on abiotic pathways remain unclear. Given that the polyphenol-Maillard reaction requires high precursor concentrations and elevated temperatures (which are not present in soil), gibbsite was used as a catalyst to overcome energetic barriers. Catechol and glycine were introduced in fixed concentrations into a phosphate-buffered solution containing gibbsite using the liquid shake-flask incubation method, while the concentration of glucose was controlled in a sterile incubation system. The supernatant fluid and HLS components were dynamically extracted over a period of 360 h for analysis, thus revealing the influence of different glucose concentrations on abiotic humification pathways. The results showed the following: (1) The addition of glucose led to a higher degree of aromatic condensation in the supernatant fluid. In contrast, the supernatant fluid without glucose (Glu0) and the control group without any Maillard precursor (CK control group) exhibited lower degrees of aromatic condensation. Although the total organic C (TOC) content in the supernatant fluid decreased in all treatments during the incubation period, the addition of Maillard precursors effectively mitigated the decreasing trend of TOC content. (2) While the C content of humic-like acid (CHLA) and the CHLA/CFLA ratio (the ratio of humic-like acid to fulvic-like acid) showed varying increases after incubation, the addition of Maillard precursors resulted in a more noticeable increase in CHLA content and the CHLA/CFLA ratio compared to the CK control group. This indicated that more FLA was converted into HLA, which exhibited a higher degree of condensation and humification, thus improving the quality of HLS. The addition of glycine and catechol without glucose or with a glucose concentration of 0.06 mol/L was particularly beneficial in enhancing the degree of HLA humification. Furthermore, the presence of glycine and catechol, as well as higher concentrations of glucose, promoted the production of N-containing compounds in HLA. (3) The presence of Maillard precursors enhanced the stretching vibration of the hydroxyl group (-OH) of HLA. After the polyphenol-Maillard reaction of glycine and catechol with glucose concentrations of 0, 0.03, 0.06, 0.12, or 0.24 mol/L, the aromatic C structure in HLA products increased, while the carboxyl group decreased. The presence of Maillard precursors facilitated the accumulation of polysaccharides in HLA with higher glucose concentrations, ultimately promoting the formation of Al-O bonds. However, the quantities of phenolic groups and phenols in HLA decreased to varying extents.

Insight into the humification and carbon balance of biogas residual biochar amended co-composting of hog slurry and wheat straw

The impact of biogas residual biochar (BRB) on the humification and carbon balance process of co-composting of hog slurry (HGS) and wheat straw (WTS) was examined. The 50-day humification process was significantly enhanced by the addition of BRB, particular of 5% BRB, as indicated by the relatively higher humic acid content (67.28 g/kg) and humification ratio (2.31) than other treatments. The carbon balance calculation indicated that although BRB addition increased 22.16-46.77% of C lost in form of CO2-C, but the 5% BRB treatment showed relatively higher C fixation and lower C loss than other treatments. In addition, the BRB addition reshaped the bacterial community structure during composting, resulting in increased abundances of Proteobacteria (25.50%) during the thermophilic phase and Bacteroidetes (33.55%) during the maturation phase. Combined these results with biological mechanism analysis, 5% of BRB was likely an optimal addition for promoting compost humification and carbon fixation in practice.

Composting of recovered rock wool from hydroponics for the production of soil amendment

Due to its fibrous structure and high water holding capacity, rock mineral wool (RMW) has boosted the development of hydroponics. Consequently, the amount of waste RMW has also increased tremendously, which has stimulated the research and development of RMW reuse options. In this study, composting and degradability of RMW from hydroponics (gRMW) were tested in combination with different ratios of biowaste compost, including physical and chemical properties of the starting and final materials, and potential ecological hazards of the final product. gRMW had high water holding capacity and low organic matter content, which was easily degradable. Limits of toxic elements according to EU regulation were not exceeded. Degraded gRMW mixtures with compost did not exhibit toxicity to plants or aquatic bacteria and showed intermediate or limited habitat function for earthworms, which preferred the sole gRMW not mixed with compost. Overall, degraded gRMW exhibited parameters of safe soil amendment.

Co-composting sugar-containing waste with chicken manure-A new approach to carbon sequestration

Improving resource use is a pressing research issue because of the huge potential organic waste market. Composting is a recycling technique, treatment to achieve the dual effect of resource recovery and zero waste. Waste composition varies: for example, chicken manure is rich in protein, straw contains wood fibres, fruit and vegetables contain sugar, and food waste contains starch. When considering combining waste streams for composting, it is important to ask if this approach can reduce overall composting costs while achieving a more concentrated result. Chicken manure, in particular, presents a unique challenge. This is due to its high protein content. The lack of precursor sugars for glucosamine condensation in chicken manure results in lower humus content in the final compost than other composting methods. To address this, we conducted experiments to investigate whether adding sugary fruits and vegetables to a chicken manure composting system would improve compost quality. To improve experimental results, we used sucrose and maltose instead of fruit and vegetable waste. Sugars added to chicken manure composting resulted in a significant increase in humic substance (HS) content, with improvements of 9.0% and 17.4%, respectively, compared to the control. Sucrose and maltose have a similar effect on the formation of humic substances. These results demonstrate the feasibility of composting fruit and vegetable waste with chicken manure, providing a theoretical basis for future composting experiments.

Elucidating carbon conversion and bacterial succession by amending Fenon-like systems during co-composting of pig manure and branch

The essential point of current study was to investigate the effect of a Fenton-like system established by oxalic acid and Fe(II) on gas emission, organic matter decomposition and humification during composting. Branches were pretreated with Fenton reagents (0.02 M FeCl2·4H2O + 1.5 M H2O2) and then adding 10 % oxalic acid (OA). The treatments were marked as B1 (control), B2 (Fenton reagent), B3 (10% OA) and B4 (Fenton-like reagent). The results collected from 80 d of composting showed that adding Fenton-like reagent benefited the degradation of organic substances, as reflected by the total organic carbon and dissolved organic carbon, and the maximum decomposition rate was observed in B4. In addition, the Fenton-like reagent could improve the synthesis of humus characterized by complex and stable compounds, which was consistent with the spectral parameters (SUVA254, SUVA280, E253/E203 and Fourier transform-infrared indicators) of DOC. Furthermore, the functional microbial succession performance and linear discriminant effect size analyses provided microbial evidence of humification improvement. Notably, compared with the control, the minimum value of CH4 cumulation was reported in B4, which decreased by 30.44 %. Concluded together, the addition of a Fenton-like reagent composed by OA and Fe(II) is a practical way to improve the humification. Furthermore, the mechanisms related to the promotion of humification should be investigated from free radicals, functional genes, and metabolic pathways.

Biochar improves the humification process during pig manure composting: Insights into roles of the bacterial community and metabolic functions

Biochar could promote humification in composting, nevertheless, its mechanism has not been fully explored from the perspective of the overall bacterial community and its metabolism. This study investigated the effects of bamboo charcoal (BC) and wheat straw biochar (WSB) on the humic acid (HA) and fulvic acid (FA) contents during pig manure composting. The results showed that BC enhanced humification more than WSB, and significantly increased the HA content and HA/FA ratio. The bacterial community structure under BC differed from those under the other treatments, and BC increased the abundance of bacteria associated with the transformation of organic matter compared with the other treatments. Furthermore, biochar enhanced the metabolism of carbohydrates and amino acids in the thermophilic and cooling phases, especially BC. Through Mantel tests and network analysis, we found that HA was mainly related to carbon source metabolism and the bacterial community, and BC might change the interaction patterns among carbohydrates, amino acid metabolism, Bacillales, Clostridiales, and Lactobacillales with HA and FA to improve the humification process during composting. These results are important for understanding the mechanisms associated with the effects of biochar on humification during composting.

Synergistic effects of Fe-based nanomaterial catalyst on humic substances formation and microplastics mitigation during sewage sludge composting

In this study, a novel Fe-based nanomaterial catalyst (Fe0/FeS) was synthesized via a self-heating process and employed to explore its impact on the formation of humic substances and the mitigation of microplastics. The results reveal that Fe0/FeS exhibited a significant increase in humic acid content (71.01 mg kg-1). Similarly, the formation of humic substances resulted in a higher humification index (4.91). Moreover, the addition of Fe0/FeS accelerated the degradation of microplastics (MPs), resulting in a lower concentration of MPs (9487 particles/kg) compared to the control experiments (22792 particles/kg). Fe0/FeS significantly increased the abundance of medium-sized MPs (50-200 μm) and reduced the abundance of small-sized (10-50 μm) and large-sized MPs (>1000 μm). These results can be attributed to the Fe0/FeS regulating the ▪OH production and specific microorganisms to promote humic substance formation and the degradation of MPs. This study proposes a feasible strategy to improve composting characteristics and reduce contaminants.

Effects of additive on formation and electron transfer capacity of humic substances derived from silkworm-excrement compost during composting

Amending biochar or MnO2 is a common strategy to regulate humification during manure composting. However, how these additives affect the formation, spectrum characteristics (UV-vis, FTIR, EEM) of humic substances (HSs) in silkworm-excrement (SE) compost and their electron transfer capacities (ETC) remains unclear. Thus, the SE composting pilot separately added with 10% corncob biochar (CB) (w/w) and 0.5% MnO2 (w/w) was run to investigate the effects. The results revealed that adding 10% CB slightly affected the HA/FA (humic acids/fulvic acids) ratios, UV-vis and FTIR spectra of the final SE-compost HSs and EEM components in the FA, but remarkably improved fulvic-like (C1)/quinone-like (C3) substances and reduced humic-like (C2)/protein-like substances (C4) in the HA. Meanwhile, 0.5% MnO2 had a noticeable positive effect on the aromatization of SE-compost FA and HA but only weak impact on SUVAs and EEM components in these HSs except C4 in the FA. Moreover, 10% CB obviously reduced EAC/EDC of FA and HA in the final SE compost by 31.1%/22.0% and 19.7%/24.0%, while MnO2 improved EDC of these HSs by 6.5%/9.1% (FA/HA). These results showed MnO2 can be used as a useful amendment to enhance the promotion effect of SE-compost HA in the soil remediation other than CB. Further investigation is suggested to focus on the effects of adding MnO2 on SE-compost HSs enhancing soil remediation and its effect on ETC derived from other manure compost.

A review of the definition, influencing factors, and mechanisms of rapid composting of organic waste

Composting is a traditional method of treating organic waste. A growing number of studies have been focusing on accelerating the process to achieve "rapid composting." However, the specific definition and influencing factors of rapid composting remain unclear. Therefore, we aimed to gather more insight into the features of rapid composting by reviewing the literature concerning organic waste composting published in the Web of Science database in the past 5 years. We selected 1615 sample studies with "composting" as the subject word and analyzed the effective composting time stated in each study. We defined rapid composting within 15 days using the median test and quartile method. Based on this definition, we summarized the influencing factors of "rapid composting," namely materials, reactors, temperature, and microorganisms. Finally, we summarized two mechanisms related to humus formation during organic waste rapid composting: high temperature-promoting maturation and microbial driving mechanisms. This literature review compiled useful references to help promote the development of rapid composting technology and related equipment.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Effect and its mechanism of potassium persulfate on aerobic composting process of vegetable wastes

Vegetable waste (VW) is a potential organic fertilizer resource. As an important way to utilize vegetable wastes, aerobic composting of VW generally has the problems of long fermentation cycle and incomplete decomposition of materials. In this study, 0.3-1.2% of potassium persulfate (KPS) was added to promote the maturity of compost. The results showed that the addition of KPS promoted the degradation of materials, accelerated the temperature rise of compost. KPS also promoted the formation of humic substances (HS). Compared with the control, HS contents of treatments with KPS addition increased by 7.81 ~ 17.52%. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis reveal the mechanism of KPS affecting the composting process: KPS stimulated the degradation of various organic substances such as lignin at high temperature stage, and the degradation of lignin could accelerate the release and decomposition of other components; KPS made the structure of the material looser, with more voids and pores, and more specific surface area of the material, which was more suitable for microbial degradation activities. Therefore, the addition of KPS can promote the decomposition of organic matter in the early stage of composting, accelerate the process of thermophilic phase, and shorten the composting process and improve product maturity.

Contact parameters calibration of mixtures in different aerobic composting period: Focusing on establishment of particle model and its flow properties

In order to calibrate the contact parameters, particle models for mixtures of each period were established by simulation of repose angle using combined models in EDEM software, and then the flow properties of mixtures in different aerobic composting periods were clarified. Results showed that compared with the six-sphere model, the use of the double-sphere model to represent the compost mixtures of each period was not only closer to the ellipsoid of the actual particles but also simplified the calculation process. The contact parameters that mostly affected the repose angle were Poisson's ratio and shear modulus of mixture in the mesophilic period and JKR surface energy in thermophilic and cooling periods. The relative errors between the simulated repose angle using the optimal parameter combination and the actual measured value were less than 2.5% indicating the reliability of the regression models at each period representing the relationship among the repose angle and significant contact parameters. In addition, the flow properties of mixtures at the mesophilic period were better than those at the thermophilic and the cooling period of its smaller repose angle, the larger mass transformation, and the smaller Ek max value. Meanwhile, mixtures in thermophilic and cooling periods had similar flow properties. Hence, these could provide information for the further application of simulation to optimize the composting process (e.g., stirring frequency and ventilation time) to promote compost maturity.

Artificial Humic Substances as Biomimetics of Natural Analogues: Production, Characteristics and Preferences Regarding Their Use

Various processes designed for the humification (HF) of animal husbandry wastes, primarily bird droppings, reduce their volumes, solve environmental problems, and make it possible to obtain products with artificially formed humic substances (HSs) as analogues of natural HSs, usually extracted from fossil sources (coal and peat). This review studies the main characteristics of various biological and physicochemical methods of the HF of animal wastes (composting, anaerobic digestion, pyrolysis, hydrothermal carbonation, acid or alkaline hydrolysis, and subcritical water extraction). A comparative analysis of the HF rates and HS yields in these processes, the characteristics of the resulting artificial HSs (humification index, polymerization index, degree of aromaticity, etc.) was carried out. The main factors (additives, process conditions, waste pretreatment, etc.) that can increase the efficiency of HF and affect the properties of HSs are highlighted. Based on the results of chemical composition analysis, the main trends and preferences with regard to the use of HF products as complex biomimetics are discussed.

Improved carbon sequestration by utilization of ferrous ions during different organic wastes composting

The humic acid (HA) possesses a more recalcitrant structure, making it crucial carbon components that improve carbon sequestration. Moreover, ferrous ions could improve microbial activity and enhance compost humification, and their oxidation into iron oxides could adsorb carbon components for sequestration. Based on the advantages of low cost and easy availability of ferrous sulfate (FeSO4), this study investigated the effect of FeSO4 on carbon sequestration during composting. Chicken manure (CM) and food waste (FW) composting were carried out in four treatments, namely control (CM, FW) and 5% (w/w) FeSO4 treated groups (CM+, FW+). Results indicated that FeSO4 increased HA content, improved organic carbon stability. Carbon loss for CM, CM+, FW and FW + treatments were 48.5%, 46.2%, 45.0%, and 40.3%, respectively. Meanwhile, FeSO4 enhanced the function of bacterial taxa involved in HA synthesis in CM + treatment, and improved the number of core bacteria significantly associated with formation of HA and iron oxide. SEM analysis verified that role of FeSO4 was significant in promoting HA synthesis during CM + composting, while it was remarkably in enhancing HA sequestration during FW + composting. This article provided fundamental theoretical backing for enhancing HA production and improving carbon sequestration during different materials composting.

Efficient recovery and characterization of humic acids from municipal and manure composts: A comparative study

The recovery of humic acids from low-quality compost obtained in municipal solid waste treatment plants provides opportunities for its valorization. This study compares the recovery and properties of the humic acids obtained from municipal mixed waste compost (MMWC) and manure compost. The effects of temperature, time, and KOH concentration on the ratio of humic acids in the extracted liquid and the content of organic carbon of the precipitates were investigated by response surface methodology. Optimal conditions were 30 °C and 24 h for both composts, with a KOH concentration of 0.53 M for MMWC and 0.25 M for manure compost. The manure compost provided a liquid extract richer in humic acids than MMWC (76.6 % vs. 33.7 %), but the precipitates presented similar organic carbon contents (38.1 % vs. 42.4 %). Regarding composition, both humic acids presented higher organic carbon and nitrogen contents than the composts used as feedstock. The extraction and further precipitation of humic acids reduced the concentration of heavy metals. Humic acids from manure compost have a slightly higher average molecular weight (2650 Da) than those from MMWC (1980 Da), while both present similar C/N ratios and degree of aromaticity. Most contaminants of emerging concern present in the original composts were not detected in the humic acids. Thus, it was demonstrated that MMWC constitutes an attractive source of humic acids with properties similar to those obtained from a high-quality compost and, therefore, with potential economic value.

Insights into antibiotic resistance gene abundances and regulatory mechanisms induced by ionic liquids during composting

This study investigated the regulatory mechanism of the evolution of antibiotic resistance genes (ARGs) during the composting process with sawdust and cow manure as raw materials using ionic liquids (ILs) pretreatment. The results showed that genes of MLS, chloramphenicol, tetracycline, beta - lactam as composting gradually decreased. From day0 to day3, MLS in control group (CK) and experimental group (T) decreased by 25.62% and 26.66%, respectively. Tetracycline decreased by 7.21% in CK and by 7.86% in T. Chloramphenicol decreased by 2.85% in CK and 3.34% in T. Beta-lactam decreased by 1.95% in Ck and by 3.69% in T. Mechanism studies have shown that ILs can effectively decompose extracellular polymeric substances (EPS) and enhance lactose dehydrogenase (LDH) release, resulting in ARGs release and elimination. Meanwhile, ILs pretreatment can inhibit growth of some ARGs hosts, especially Firmicutes, resulting in decreased ARGs. Moreover, metabolic pathways and related genes take part in ARGs transmission were down regulated, leading to decreased ARGs.

Sulfur-aided aerobic biostabilization of swine manure and sawdust mixture: Humification and carbon loss

To investigate how sulfur addition affects humification and carbon loss during swine manure (SM) biostabilisation, various proportions of sulfur, i.e., 0 (CK), 0.2%-0.8% (S1-S4) were added to SM in a 70-day pilot-scale test. Compared to CK (16.07%), sulfur addition resulted in the mineralization of 17.05%-24.27% of the total organic carbon. Sulfur addition also reduced CH4 emissions, which were 3.7%-29.3% lower than that of CK. The total global warming potential values were in the range of 913.1-968.2 g CO2 eq kg-1 for all treatments. Although the sulfur-added treatments showed lower HA/FA ratios than CK after 70 days, no significant impact on the maturity of the final products was observed. Sulfur addition impacted the microbial community, CH4, CO2, N2O emissions, and affected the variation of temperature in biowaste biostabilization. These discoveries provided an important basis for understanding the function of sulfur in regulating the aerobic bio-decomposition of organic waste.

A novel composting system for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer

Ammonia emissions not only lead to environmental pollution but also reduce the quality of compost products. Here, a novel composting system (condensation return composting system, CRCS) was designed for mitigating ammonia emissions. The results showed that the CRCS reduced ammonia emissions by 59.3% and increased the total nitrogen content by 19.4% compared with the control. By integrating the results of nitrogen fraction conversion, ammonia-assimilating enzyme activity, and structural equation modeling, it was found that the CRCS facilitated the conversion of ammonia to organic nitrogen by stimulating ammonia-assimilating enzyme activity and ultimately retained nitrogen in the compost product. Moreover, the pot experiment confirmed that nitrogen-rich organic fertilizer produced by the CRCS significantly increased the fresh weight (45.0%), root length (49.2%), and chlorophyll content (11.7%) of pakchoi. This study provides a promising strategy for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer with high agronomic value.

Evaluation of fungal dynamics during sheep manure composting employing peach shell biochar

In this study, explored the influence of different proportion (0%, 2.5%, 5%, 7.5%, and 10%) peach shell biochar (PSB) with microbial agents (EM) on the carbon transformation, humification process and fungal community dynamics during sheep manure (SM) composting. And no additives were used as control. The results manifested that the CO2 and CH4 emissions were effectively reduced 8.23%∼13.10% and 17.92%∼33.71%. The degradation rate of fulvic acid increased by 17.12%∼23.08% and the humic acid contents were enhanced by 27.27%∼33.97% so that accelerated the composting. Besides, the dominant fungal phylum was Ascomycota (31.43%∼52.54%), Basidiomycota (3.12%∼13.85%), Mucoromycota (0.40%∼7.61%) and Mortierellomycota (0.97%∼2.39%). Pearson correlation analysis and network indicated that there were different correlations between physicochemical indexes and fungal community under different additive concentrations. In brief, the two modifiers application promoted the SM degradation and affected the fungal community structure.

Iron reduction in composting environment synergized with quinone redox cycling drives humification and free radical production from humic substances

The aim of this paper was to investigate the influence of Fe (III) on humification and free radicals evolution. The experimental data showed that the experimental group (CT) with Fe₂(SO₄)₃ had a better degree of humification than the control group (CK). The humic substances (HS) content was 10% higher in CT (23.94 mg·g^-1) than in CK (21.54 mg·g^-1) in the final. Fe (III) contributed significantly to the formation of free radicals in HS. The amount of H₂O₂ in CT increased to 74.8 mmol·kg^-1, while CK was only 46.5 mmol·kg^-1. The content of semiquinone free radical was 10.32×10¹¹ spins/mm³ in CT, 5.11×10¹¹ spins/mm³ in CK in the end. Several iron-reducing bacteria were detected in composting, among which Paenibacillus was dominant. The above findings suggested that the application of Fe₂(SO₄)₃ enhanced the iron reduction synergistic quinone redox cycling and promoted the generation of free radicals during the humification of composting.

Sustainable management and recycling of anaerobic digestate solid fraction by composting: A review

The aim of the study was to review and discuss the management and recycling of anaerobic digestate solid fraction by composting process in the context of circular bioeconomy and sustainable development. The conversion of the solid fraction into compost can be recognized as novel process-enhancing supplements for land reclamation. Moreover, the solid fraction of the digestate is a valuable substrate for compost production, both as a monosubstrate and as a valuable additive for other raw materials to enrich in organic matter. These results should serve as reference point to target adjusting screws for anaerobic digestate solid fraction by composting process improvement, its implementation in modern bioeconomy perspective as well as provide a guideline for effective waste management.

Pretreatment and composting technology of agricultural organic waste for sustainable agricultural development

With the continuous development of agriculture, Agricultural organic waste (AOW) has become the most abundant renewable energy on earth, and it is a hot spot of research in recent years to realize the recycling of AOW to achieve sustainable development of agricultural production. However, lignocellulose, which is difficult to degrade in AOW, greenhouse gas emissions, and pile pathogenic fungi and insect eggs are the biggest obstacles to its return to land use. In response to the above problems researchers promote organic waste recycling by pretreating AOW, controlling composting conditions and adding other substances to achieve green return of AOW to the field and promote the development of agricultural production. This review summarizes the ways of organic waste treatment, factors affecting composting and problems in composting by researchers in recent years, with a view to providing research ideas for future related studies.

A review of additives use in straw composting

Straw composting is not only a process of decomposition and re-synthesis of organic matter, but also a process of harmless treatment, avoiding air pollution caused by straw burning. Many factors, including raw materials, humidity, C/N, and microbial structure, may determine the composting process and the quality of final product. In recent years, many researches have focused on composting quality improvement by adding one or more exogenous substances, including inorganic additives, organic additives, and microbial agents. Although a few review publications have compiled the research on the use of additives in composting, none of them has specifically addressed the composting of crop straw. Additives used in straw composting can increase degradation of recalcitrant substances and provide ideal living surroundings for microorganism, and thus reduce nitrogen loss and promote humus formation, etc. This review's objective is to critically evaluate the impact of various additives on straw composting process, and analyze how these additives enhance final quality of composting. Furthermore, a vision for future perspectives is provided. This paper can serve as a reference for straw composting process optimization and composting end-product improvement.