Enhancement Of Aerobic Composting Process Of Food Waste And Its Mechanism

The production of food waste in China has increased dramatically with the accelerated urbanization process,which has led to increasingly prominent environmental pollution problems.Aerobic composting,as one of the effective means for resource treatment of food waste,still suffers from slow start-up rate,long treatment cycle and low degree of humification.This paper aims to establish an enhanced process for the aerobic composting of food waste by using hollow bamboo sphere based on bamboo as additive and thermotolerant lignin-degrading bacteria as inoculants.The high-throughput sequencing technology was used to clarify the molecular mechanism of the composting process enhanced by bamboo sphere and thermotolerant lignin-degrading bacteria,and to explore the impact of food waste organic fertilizer on the remediation of antimony contaminated soil.The main research contents and results are as follows:(1)A process for strengthening the aerobic composting of food waste with bamboo sphere has been established.By adding different proportions of bamboo sphere for aerobic composting of food waste,the results showed that adding 6%bamboo sphere had the best effect.This treatment could quickly start composting,prolong the thermophilic period(12 d),and increase the organic matter degradation rate and the contents of total nitrogen(TN),total phosphorus(TP),total potassium(TK),and humic acid(HA)in the end product by 54.17%,13.61%,19%,17.42%and 68.3%,respectively,compared to the control.A comprehensive evaluation of the maturity degree was conducted based on multiple indicators,proving that the addition of 6%bamboo sphere shortened the maturation period(42 days),improved the degree of humification and maturity;Spectroscopy studies show that aromatic C=C structure,humic acid-like substances,and components with complex ring structures are improved by the addition of bamboo sphere.(2)The microbial community succession pattern during the composting of food waste enhanced by bamboo sphere was analyzed.Microbial diversity analysis showed that the addition of bamboo sphere resulted in a richer and more diverse microbial community in the compost pile.Analysis at the phylum and genus levels showed that the addition of bamboo sphere stimulated the growth of the bacteria Firmicutes,Bacillus and Actinobacteria,and the fungi Aspergillus,Issatchenkia,Thermoascus and Microascus during the thermophilic and maturation periods,which not only possess heat resistance and deodorization properties,but also produce proteases,lipases,and cellulases.The linear discriminant analysis Effect Size(LEf Se)analysis further demonstrated that Firmicutes,Thermoascaceae and Actinobacteriota were significantly enriched in the bamboo sphere group.Canonical correspondence analysis(CCA)showed that TK,TP and total organic carbon had significant effects on the succession of bacterial and fungal communities during composting.(3)Thermotolerant lignin-degrading bacteria were screened,and their mechanism of lignin degradation was analyzed.Two thermotolerant(50°C)lignin-degrading bacteria were screened from the soil of the Central South University campus.They were identified as Bacillus sp.LD2(LD2)and novel species Aneurinibacillus sp.LD3(LD3),which degraded lignin by up to 48.38%and 61.28%,respectively.Gel permeation chromatography analysis demonstrated that the 2 strains can cause lignin to undergo delignification reactions,leading to the production of smaller monomeric compounds through depolymerization.The results of enzyme activity analysis showed that strain LD3 had better ability to produce Lignin Peroxidase(Li P),Laccase(Lac),and Manganese Peroxidase(Mn P)than strain LD2.Gas chromatograph-mass spectrometer analysis showed that the strain LD3 degrades lignin through the steps ofβ-aryl ether and biphenyl bond breaking,aromatic ring oxidative cleavage and Cα-Cβcleavage by secreting ligninolytic enzyme.(4)The effect of inoculation with thermotolerant lignin degrading bacteria on the aerobic composting process of food waste was studied.The results showed that inoculation with LD3 increased the maximum temperature to 59.3°C and maintained the thermophilic period up to 14 d.The decomposition rates of organic matter,hemicellulose,cellulose and lignin in this group were 20.11%,31.56%,31.65%and 18.64%,respectively.The final contents of TN,TP and TK were 4.2%,26.75%and 81.47%higher than the initial values,which were significantly higher than those in control.The analysis of humic fractions showed that LD3inoculation could improve the stability and humification of the final product by promoting the conversion of the composting material to the more stable HA.The assessment of the combined maturity indicators showed that inoculation with LD3 reduced the ratio of carbon to nitrogen(C/N)to 15.66 and the maturation cycle to 36 d.Spectroscopy studies show that higher fluorescence intensity of aromatic C=C and humic acid-like substances in the LD group than in control.(5)The molecular mechanism of the enhanced composting of food waste by thermotolerant lignin-degrading bacteria was elucidated.Microbial community succession analysis showed that thermophilic bacteria,phosphorus solubilizing bacteria,lignocellulolytic bacteria,and functional microorganisms that produce antibiotics were relatively abundant in the LD group,including bacteria Proteobacteria、Bacteroidota、Firmicutes、Actinobacteriota、Aneurinibacillus、Bacillus and Pseudomonas,as well as fungi Ascomycota and Trichocomaceae＿Unclassified,while the reproduction of the opportunistic human pathogen Candida is inhibited.LEf Se analysis shows that Bacteroidota,Proteobacteria,Firmicutes and Ascomycota were the unique biomarkers of LD group,which involve carbon nitrogen cycle and lignocellulose degradation.Metabolic function prediction showed that inoculation with LD3 increased the sequence involved in carbohydrate and amino acid metabolism.Saprotroph was the predominant fungal trophic mode in composting,and inoculation with LD3 has a better inactivation effect on animal and plant pathogenic fungi during composting.Aneurinibacillus was significantly positively correlated with temperature,TP,Bacillus,and Thermoactinomyces.The most significant factor affecting the fungal community structure in the LD group was temperature.(6)The effect of food waste organic fertilizer(FOF)on the remediation of antimony-contaminated soil was explored.The analysis of soil physicochemical properties shows that the application of FOF has the most significant effect on reducing bulk density(from 1.57 to 1.08 g/cm~3),improving salinization degree,and increasing organic matter and available NPK contents.Compared to the control,the plant height of Pteris vittate increased by 82.12%and 60.23%in the FOF and commercially available sheep manure organic fertilizer groups,respectively.Both organic fertilizers were more effective than inorganic fertilizer in reducing the total antimony content of the soil.Analysis of antimony valence transformation showed that FOF application promoted oxidative detoxification of Sb(III)to produce Sb(V)in soil.Microbial community analysis showed that the application of FOF could promote the enrichment of Proteobacteria、Actinobacteria、Firmicutes and Bacteroidetes phylum in Pteris vittate roots,in particular,specific microbial groups such as Acinetobacter、Sphingomonas、Comamonas、Bradyrhizobium、Alphaproteobacteria、Acidovorax and Paenibacillaceae possessing Sb(III)oxidation,nitrogen fixation and phosphorus and potassium solubilisation functions to alleviate the stress on the growth of Pteris vittate from poor soil conditions and heavy metals in mines.In summary,this paper establishes an enhanced process for aerobic composting of food waste based on bamboo sphere additive and thermotolerant lignin degrading bacteria inoculant.It also reveals the effectiveness and ecological mechanism of food waste organic fertilizer for the remediation of antimony-contaminated soil.This not only provides theoretical guidance and technical support for the development of organic solid waste resources in China,but also provides a new approach for the promotion and application of food waste organic fertilizer and the remediation of antimony-contaminated sites.