Impact of wine grape pomace on humification performance and microbial dynamics during pig manure composting

Improving Aerobic Digestion of Food Waste by Adding a Personalized Microbial Inoculum

In the context of China's garbage classification policy, on-site aerobic food waste (FW) digestion is crucial for reducing transportation and disposal costs. The efficiency of this process is largely determined by the microbial community structure and its functions. Therefore, this study aimed to analyze the impact of a personalized microbial consortium (MCM) on the efficiency of aerobic FW digestion and to reveal the underlying mechanisms. An MCM, sourced from naturally degrading FW, was selected to enrich degrading bacteria with relatively high hydrolyzing ability. The functionality of the MCM was evaluated by tracing the successions of microbial communities, and comparing the differences in the forms of organic compounds, metabolic functions, and hydrolase activities. X-ray photoelectron spectroscopy demonstrated that the MCM metabolized faster, and produced more acidic metabolites. Metagenomic analysis indicated that FW inoculated with the personalized MCM increased abundance of Bacillaceae producing hydrolysis enzymes and promoted glycolysis metabolic pathways, enhancing energy generation for metabolism, compared to the commercial effective bacterial agent. This paper provides both theoretical and practical evidence for the improvement of biochemical processor of FW with the personalized MCM, which has promising application prospects and economic value.

The maturity, humus content, and microbial metabolic function of sheep manure compost on the Qinghai-Tibet Plateau can be significantly improved by reducing the moisture content

The Qinghai-Tibet Plateau (QTP) is characterized by an extreme hypoxia, which may lead to lack of sufficient oxygen for compost production, and thus seriously affecting the compost quality. The moisture content (MC) has a direct effect on the oxygen content of composting pile. At present, the research on the optimum moisture content of compost production on the QTP is still lacking. This study aimed to investigate the influences of MC on fermentation quality of sheep manure composting on the QTP and to further analyze the changes of microbial metabolic function and enzyme activity under different MC. Composting experiment with low MC (45%) and conventional MC (60%) was conducted in both summer and autumn. The results showed that the composting efficiency of 45% MC was better than 60% in both seasons, which was mainly manifested as longer high-temperature period (summer:16 d vs 14 d, autumn: 7 d vs 2 d), higher germination index (summer:136.1% vs 128.6%, autumn:103.5% vs 81.2%), and more humus synthesis (summer:159.8 g/kg vs 151.2 g/kg, autumn:136.1 k/kg vs 115.5 k/kg). The 45% MC can improve microbial metabolism, including increasing the abundance of functional genes involved in carbohydrate metabolism, amino acid metabolism, and nucleotide metabolism and improving the activities of cellulase, β-glucosidase, protease, polyphenol oxidase, and peroxidase. In conclusion, 45% MC can improve the fermentation efficiency and products quality of sheep manure compost on QTP.

Key Role of Vegetation Cover in Alleviating Microplastic-Enhanced Carbon Emissions

Microplastics (MPs) are considered to influence fundamental biogeochemical processes, but the effects of plant residue-MP interactions on soil carbon turnover in urban greenspaces are virtually unknown. Here, an 84-day incubation experiment was constructed using four types of single-vegetation-covered soils (6 years), showing that polystyrene MP (PSMP) pollution caused an unexpectedly large increase in soil CO2 emissions. The additional CO2 originating from highly bioavailable active dissolved organic matter molecules (<380 °C, predominantly polysaccharides) was converted from persistent carbon (380-650 °C, predominantly aromatic compounds) rather than PSMP derivatives. However, the priming effect of PSMP derivatives was weakened in plant-driven soils (resistivity: shrub > tree > grass). This can be explained from two perspectives: (1) Plant residue-driven humification processes reduced the percentage of bioavailable active dissolved organic matter derived from the priming effects of PSMPs. (2) Plant residues accelerated bacterial community succession (dominated by plant residue types) but slowed fungal community demise (retained carbon turnover-related functional taxa), enabling specific enrichment of glycolysis, the citric acid cycle and the pentose phosphate pathway. These results provide a necessary theoretical basis to understand the role of plant residues in reducing PSMP harm at the ecological level and refresh knowledge about the importance of biodiversity for ecosystem stability.

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.

Synergistic effect triggered by Fe2O3 and oxygen-induced hydroxyl radical enhances formation of amino-phenolic humic-like substance

Metal oxides play a promising role in the transformation of polyphenols and amino acids involved in naturally occurring humification. The objective of this study was to explore the synergistic interactions between Fe2O3 and O2 in the formation of humic substances under a controlled O2 atmosphere (0%, 21% and 40% O2 levels). The results indicate that an O2 level of 21% with Fe2O3 was optimal for humic acid (HA) production. Hydroxyl radicals (∙OH) formed and promoted the formation of HA in the presence of O2, and O2 improved the enhancing capacity of Fe2O3 by oxidizing Fe(II) to Fe(III). Moreover, the combination of these processes resulted in a synergistic improvement in humification. The evolution of functional groups in HA suggested that O2 promoted the formation of oxygen-containing groups such as lipids, and Fe2O3 was conducive to the formation of dark-coloured polymers during the darkening process of humification. Furthermore, the O2 level of 40% inhibited the formation of HA by reducing the transformation from Fe(III) to Fe(II). The XRD results showed few changes in the composition of Fe2O3 before and after humification, which indicated that Fe2O3 was a catalyst and an oxidant. The heterospectral UV-Vis/FTIR results suggested that ∙OH attacked phenolic rings to form the aromatic ring skeleton of HA and benefit the ring-opening copolymerization of humic precursors. In addition, structural equation modelling demonstrated that dissolved Fe was the key parameter affecting the HA yield. These findings provide new insights into the synergism of O2-mediated ∙OH production associated with metal oxide-facilitated humification.

Effect of the inoculation of Phanerochaete chrysosporium on nitrogen migration and organic matter conversion during electrolytic manganese residue composting

Composting has made it practicable to dispose electrolytic manganese residues (EMR) in a less toxic way, nevertheless, the decomposition and the loss of nitrogen is a critical issue. This study aimed to investigate the role of Phanerochaete chrysosporium (PC) inoculation on nitrogen migration and promotion of decomposing organic matter (OM), as well as the effect on bacterial community structure during EMR composting. The results exhibited that nitrogen loss tallied with the first-order kinetic model. PC inoculation increased the relative microbial abundance of Firmicutes, which improved the efficiency of nitrogen nitrification and OM degradation, and increased the germination index and total nitrogen content by 13.8% and 2.95 g/kg, respectively. Moreover, aromatic benzenes replaced heteropolysaccharides, alcohols and ethers as the main components of OM in fertilizer, leading up to a more stable humus structure. This study provides a rationale and a novel perspective on the resource and nutrient conservation of EMR-contaminated soils.

Product maturation and antibiotic resistance genes enrichment in food waste digestate and Chinese medicinal herbal residues co-composting

The land application of food waste digestate (FWD) requires a composting process to improve its soil amendment performance and alleviate environmental risks. This study proposed co-composting of Chinese medicinal herbal residues (CMHRs) and FWD as a means to improve the maturation performance and investigated the evolution of antibiotic resistance genes (ARGs). Results demonstrated that CMHRs addition effectively accelerated the maturity of FWD composting to less than 35 days, remarkably removed its remaining antibiotics by 83.0% and promoted the formation of humification substances. However, both quantitative PCR and 16S rRNA sequencing analysis indicated that a significant enrichment of ARGs and mobile genetic elements including frA1, tetX, blaTEM, InuB-01, aadA2-02 and IntI-1 was observed via the co-composting of FWD and CMHRs. These results indicated that the land application of products obtained from FWD and CMHRs co-composting is at risk of spreading ARGs, although the composting process could be significantly improved.

Enhanced removal organic compounds and particles from cooking fume using activated sludge scrubber filled loofah: From performance to the mechanism

The catering industry's growth has resulted in cooking fume pollution becoming a major concern in people's lives. As a result, its removal has become a core research focus. Natural loofah is an ideal biofilm carrier, providing a conducive environment for microorganisms to grow. This study utilized natural loofah to fill domesticated activated sludge in a bioscrubber, forming biofilms that enhance the ability to purify cooking fume. This study found that the biomass of loofah biofilms per gram is 104.56 mg. The research also determined the removal efficiencies for oils, Non-methane total hydrocarbons (NMHC), PM2.5, and PM10 from cooking fumes, which were 91.53%, 67.53%, 75.25%, and 82.23%, respectively. The maximum elimination capacity for cooking fumes was found to be 20.7 g/(m3·h). Additionally, the study determined the kinetic parameters for the biodegradation of oils (Kc and Vmax) to be 4.69 mg L-1 and 0.026 h-1, respectively, while the enzyme activities of lipase and catalase stabilized at 75.50 U/mgprots and 67.95 U/mgprots. The microbial consortium identified in the biofilms belonged to the phylum Proteobacteria and consisted mainly of Sphingomonas, Mycobacterium, and Lactobacillus, among others.

Effects of turning frequency on fermentation efficiency and microbial community metabolic function of sheep manure composting on the Qinghai-Tibet Plateau

This study explored the effects of turning frequency on fermentation efficiency and microbial metabolic function of sheep manure composting on the Qinghai-Tibet Plateau (QTP). Five treatments with different turning frequencies were set up in this study: turning every 1 day (T1), 2 days (T2), 4 days (T3), 6 days (T4), and 8 days (T5). Results showed that the high temperature period for T1 and T5 lasted only 4 days, while that for T2-T4 lasted more than 8 days. The germination index of T1 and T5 was lower than 80%, while that of T2-T4 was 100.6%, 97.8%, and 88.6%, respectively. This study further predicted the microbial metabolic function of T2-T4 using the bioinformatics tool PICRUSt2 (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) and determining the activities of various functional enzymes. The results showed that carbohydrate metabolism, protein metabolism, and nucleotide metabolism were the main metabolic pathways of microorganisms, and that T2 increased the abundance of functional genes of these metabolic pathways. The activities of protease, cellulase, and peroxidase in T2 and T3 were higher than those in T4, and the effect of T2 was more significant. In conclusion, turning once every 2 days can improve the quality of sheep manure compost on the QTP.

Bacterial community dynamics and co-occurrence network patterns during different stages of biochar-driven composting

Bacterial communities were dynamically tracked at four stages of biochar-driven sheep manure pile composting, and the co-occurrence networks with keystone taxa were established. The succession of bacterial community obvious varied during the composting process, Proteobacteria predominant in initial stage (39%) then shifted into Firmicutes in thermophilic (41%) and mesophilic (27%) stages, finally the maturation stage dominant by Bacteroidota (26%). Visualizations of bacterial co-occurrence networks demonstrate more cooperative mutualism and complex interactions in the thermophilic and mesophilic phases. Noticeably, the 7.5 and 10% biochar amended composts shown highest connections (736 and 663 total links) and positive cooperation (97.37 and 97.13% positive link) as well as higher closeness centrality and betweenness centrality of keystone taxa. Overall, appropriate biochar addition alters bacterial community succession and strengthens connection between keystone taxa and other bacteria, with 7.5 and 10% biochar amended composts has intense mutualistic symbiosis among bacterial communities.

Microbial metabolism and humic acid formation in response to enhanced copper and zinc passivation during composting of wine grape pomace and pig manure

Copper (Cu) and zinc (Zn) in piglet feed can lead to heavy metals (HMs) accumulation in pig manure (PM). Composting is crucial for recycling biowaste and decreasing HMs bioavailability. This study aimed to investigate the impact of adding wine grape pomace (WGP) on the bioavailability of HMs during PM composting. WGP facilitated the passivation of HMs through Cytophagales and Saccharibacteria_genera_incertae_sedis which promoted the formation of humic acid (HA). Polysaccharide and aliphatic groups in HA dominated the transformation of chemical forms of HMs. Moreover, adding 60% and 40% WGP enhanced the Cu and Zn passivation effects by 47.24% and 25.82%, respectively. Polyphenol conversion rate and core bacteria were identified as key factors in affecting HMs passivation. These results offered new insights into the fate of HMs during PM composting in response to the addition of WGP, which is helpful to practical application of WGP to inactivate HMs for improving compost quality.

Enhanced enzymatic saccharification and ethanol production of corn stover via pretreatment with urea and steam explosion

Enhancing the degradation of lignocellulosic structure is essential for the efficient use of corn stover. This study investigated the effects of using urea combined with steam explosion on the enzymatic hydrolysis and ethanol production of corn stover. The results demonstrated that 4.87% urea addition and 1.22 MPa steam pressure were optimal for ethanol production. The highest reducing sugar yield (350.12 mg/g) was increased by 116.42% (p < 0.05), and the corresponding degradation rates of cellulose, hemicellulose, and lignin in pretreated corn stover were increased by 40.26%, 45.89% and 53.71% compared with the untreated corn stover (p < 0.05). Moreover, the maximal sugar alcohol conversion rate was approximately 48.3%, and the ethanol yield reached 66.5%. In addition, the key functional groups in corn stover lignin under combined pretreatment were identified. These findings offer new insights into corn stover pretreatment and can help develop feasible technologies to enhance ethanol production.

Manganese dioxide eliminates the phytotoxicity of aerobic compost products and converts them into a plant friendly organic fertilizer

This study mainly confirmed the exogenous substances (pomace, biochar, MnO₂) and the quorum sensing of bacterial communities jointly regulate the metabolic conversion of toxic substances in manures and agricultural wastes, and converts them into a plant-friendly organic fertilizer through aerobic composting and pot experiment. The results showed the composting products had positive performance in bacterial communities, physicochemical indicators, and phytotoxicity. Meanwhile, the addition of exogenous substances could significantly improve seed germination index, promote metabolites conversion, and optimize bacterial community structure. Furthermore, the exogenous substances mainly regulated the functions of the three bacterial communities by quorum sensing system, then promoted the beneficial metabolites, and inhibited the harmful metabolites. Finally, pot experiments suggested compost products could significantly promote plant growth. Thus, these important discoveries extend the knowledge of the previous work and provide an economical and simple method to convert wastes into organic fertilizers that are friendly to plants and soil.

Effect of biochar addition on copper and zinc passivation pathways mediated by humification and microbial community evolution during pig manure composting

The mobility and bioavailability of Cu and Zn are the main threats associated with the land application of pig manure (PM) compost products. This study investigated the impacts of biochar (BC) concentration on passivation of Cu and Zn associated with the compost maturity. The results indicated that 15% and 10% BC favoured the passivation of Cu and Zn, respectively. BC promoted passivation of Cu by accelerating HA production and optimized the abundance of Firmicutes. BC promoted the passivation of Zn by increasing the high temperature peak and the corresponding pH (8-8.5). A higher level (15% and 20%) of BC altered the dominant bacterial phylum from Firmicutes to Proteobacteria. 20% BC inhibited the passivation of Cu and Zn by reducing the highest temperature and lowering the alkalinity of substrate. These results offer new insights into understanding how the addition of BC could reduce the risk of hazardous products during PM composting.

Dynamics of microbiota and physicochemical characterization of food waste in a new type of composter

Organic wastes are considered the most significant components of urban solid waste, negatively affecting the environment. It is essential to use renewable resources to minimize environmental risks. Composting is one of the most sustainable methods for managing organic waste and involves transforming organic matter into a stable and nutrient-enriched biofertilizer, through the succession of microbial populations into a stabilized product. This work aimed to evaluate the efficiency of the new type of composter and the microbial and physiochemical dynamics during composting aiming to accelerate the degradation of organic waste and produce high-quality compost. Two inoculants were evaluated: (1) efficient microorganisms (EM); (2) commercial inoculum (CI), which were compared to a control treatment, without inoculation. Composting was performed by mixing organic waste from gardening with residues from the University's Restaurant (C/N ratio 30:1). The composting process was carried out in a 1 m3 composter with controlled temperature and aeration. The thermophilic phase for all treatments was reached on the second day. Mature compost was obtained after an average of 120 days, and composting in all treatments showed an increase in the availability of P and micronutrients. The new composter helped to accelerate the decomposition of residues, through the maintenance of adequate oxygen content and temperature control inside the cells, providing high metabolic activity of microorganisms, contributing to an increase in physicochemical characteristics, also reducing the composting time in both treatments. During composting, the bacteria and actinobacteria populations were higher than yeasts and filamentous fungi. The inoculated treatments presented advantages showing more significant mineralization of P-available and micronutrients such as Mn and Zn in terms of the quality of the final product in comparison to the control treatment. Finally, the new composter and the addition of inoculants contributed significantly to the efficiency of the process of composting organic waste.