Relationship between bacterial diversity and environmental parameters during composting of different raw materials

Effect of Phanerochaete chrysosporium inoculation on bacterial community and metal stabilization in lead-contaminated agricultural waste composting

The effects of Phanerochaete chrysosporium inoculation on bacterial community and lead (Pb) stabilization in composting of Pb-contaminated agricultural waste were studied. It was found that the bioavailable Pb was transformed to stable Pb after composting with inoculum of P. chrysosporium. Pearson correlation analysis revealed that total organic carbon (TOC) and carbon/nitrogen (C/N) ratio significantly (P<0.05) influenced the distribution of Pb fractions. The richness and diversity of bacterial community were reduced under Pb stress and increased after inoculation with P. chrysosporium. Redundancy analysis indicated that C/N ratio, total organic matter, temperature and soluble-exchangeable Pb were the significant parameters to affect the bacterial community structure, solely explained 14.7%, 11.1%, 10.4% and 8.3% of the variation in bacterial community composition, respectively. In addition, the main bacterial species, being related to organic matter degradation and Pb stabilization, were found. These findings will provide useful information for composting of heavy metal-contaminated organic wastes.

Gentamicin degradation and changes in fungal diversity and physicochemical properties during composting of gentamicin production residue

An indoor co-composting of gentamicin fermentation residues (GFR) and lovastatin fermentation residues (LFR) inoculated with gentamicin-degrading Aspergillus terreus FZC3 was conducted to remove gentamicin residues. The results showed that treatment MFZC3, consisting of a 10:1 blend of GFR and LFR (w/w), had the longest thermophilic phase (7days), quickest gentamicin degradation (t_½=4.4days), and relatively higher gentamicin degradation percentage (96.7%) at the end of composting. Addition of Aspergillus terreus FZC3 affected fungal diversity of the compost and improved the removal of gentamicin during composting of the 15:1 GFR:LFR blend. By analyzing the variations of gentamicin and fungal community dynamics, it was speculated that Aspergillus terreus could accelerate gentamicin degradation. The microbial community and dynamic during composting were deeply affected by the physicochemical properties, and vice versa. In conclusion, co-composting of GFR with LFR could be a promising technology to solve the problem of gentamicin residue in GFR waste.

Effect of cold-adapted microbial agent inoculation on enzyme activities during composting start-up at low temperature

In order to put forward a method to promote composting start-up at low ambient temperature, the cold-adapted microbial agent (CAMA) was inoculated in chicken manure (CM), and compared the enzymes activities, including urease, proteases, β-glucosidase and invertase, with no CAMA group (CK). In this study, the temperature of CM reached 50°C in 53h, but it in CK was only around 30°C during the composting process. Moreover, the enzymes exhibited higher activity in CM than CK, indicating the effectiveness of CAMA. Furthermore, redundancy analysis was conducted to study the relationships of CAMA, with enzymes activities and temperature. Results showed that the positive effect of CAMA on the enzyme activities were achieved by affecting the bacterial community structure. Accordingly, we provide a method to guide CAMA inoculation for promoting compost start-up in cold area.

Identifying the key factors that affect the formation of humic substance during different materials composting

The aim of this work was to identify the factors which can affect humic substance (HS) formation. Composting periods, HS precursors, bacteria communities and environment factors were recognized as the key factors and few studies explored the potential relationships among them. During composting, HS precursors were mainly formed in the heating and thermophilic phases, but HS were polymerized in the cooling and mature phases. Moreover, bacterial species showed similar classification of community structure in the same composting period of different materials. Furthermore, structural equation model showed that NH₄^--N and NO₃^--N were the indirect environmental factors for regulating HS formation by the bacteria and precursors as the indirect and direct driver, respectively. Therefore, both environmental factors and HS precursors can be the regulating factors to promote HS formation. Given that, a new staging regulating method had been proposed to improve the amount of HS during different materials composting.

Impact of phosphate-solubilizing bacteria inoculation methods on phosphorus transformation and long-term utilization in composting

This study aimed to assess the effect of phosphate-solubilizing bacteria (PSB) application and inoculation methods on rock phosphate (RP) solubilization and bacterial community during composting. The results showed that PSB inoculation in different stages of composting, especially both in the beginning and cooling stages, not only improved the diversity and abundance of PSB and bacterial community, but also distinctly increased the content of potential available phosphorus. Redundancy analysis indicated that the combined inoculation of PSB in the initial stage with higher inoculation amount and in the cooling stage with lower inoculation amount was the best way to improve the inoculation effect and increase the solubilization and utilization of RP during composting. Besides, we suggested three methods to improve phosphorus transformation and long-term utilization efficiency in composts based on biological fixation of phosphates by humic substance and phosphate-accumulating organisms.

New insight with the effects of biochar amendment on bacterial diversity as indicators of biomarkers support the thermophilic phase during sewage sludge composting

In this work, the 16S rRNA gene was used to compare the bacterial diversity at thermophilic stage of six different biochar dosage applied SS composting, while compared without biochar added treatment or control. The results showed that biochar amendment affected the structure and succession of bacteria diversity in different ways, and there were 35 prominent genera among all samples displayed in the species abundance heat-map. Among them, Proteobacteria, Firmicutes and Chloroflexi were the main phyla found in genomic libraries from each treatment. The most abundant common genera among the all treatments were Pseudomonas, T78, Acinetobacter and Ureibacillus. In addition, Krona, principal component analysis and β-diversity indices showed a clear difference in bacterial diversity among the biochar added and control treatments. Finally, our results suggested that Planomicrobium, Paracoccus, Agrobacterium and Devosia could be considered as possible biomarkers symbolic of the thermophilic phase during SS composting.

A new model to predict diffusive self-heating during composting incorporating the reaction engineering approach (REA) framework

During composting, self-heating may occur due to the exothermicities of the chemical and biological reactions. An accurate model for predicting maximum temperature is useful in predicting whether the phenomena would occur and to what extent it would have undergone. Elevated temperatures would lead to undesirable situations such as the release of large amount of toxic gases or sometimes would even lead to spontaneous combustion. In this paper, we report a new model for predicting the profiles of temperature, concentration of oxygen, moisture content and concentration of water vapor during composting. The model, which consists of a set of equations of conservation of heat and mass transfer as well as biological heating term, employs the reaction engineering approach (REA) framework to describe the local evaporation/condensation rate quantitatively. A good agreement between the predicted and experimental data of temperature during composting of sewage sludge is observed. The modeling indicates that the maximum temperature is achieved after some 46weeks of composting. Following this period, the temperature decreases in line with a significant decrease in moisture content and a tremendous increase in concentration of water vapor, indicating the massive cooling effect due to water evaporation. The spatial profiles indicate that the maximum temperature is approximately located at the middle-bottom of the compost piles. Towards the upper surface of the piles, the moisture content and concentration of water vapor decreases due to the moisture transfer to the surrounding. The newly proposed model can be used as reliable simulation tool to explore several geometry configurations and operating conditions for avoiding elevated temperature build-up and self-heating during industrial composting.

Co-composting of vegetable wastes and carton: Effect of carton composition and parameter variations

The aim of the study was to investigate the effects of carton in the composting process of mixed vegetable wastes using an experimental composter of capacity 80L. Three different mixes were set-up (Mixes 1, 2 and 3) which consisted of vegetable wastes, 2.0kg paper and bulking agents, vegetable wastes, 1.5kg carton and bulking agents, vegetable wastes, 4.5kg carton and bulking agents, respectively. Temperature evolution, pH trends, moisture levels, respiration rates, percentage volatile solids and electrical conductivity were monitored for a period of 50days. The system remained under thermophilic conditions for a very short period due to the small size of the reactor. The three mixes did not exceed a temperature of 55°C, where sanitization takes place by the destruction of pathogens. The highest peak of CO₂ evolution was observed in Mix 2 indicating that maximum microbial degradation took place in that mix.

Effect of precursors combined with bacteria communities on the formation of humic substances during different materials composting

The aim of this work was to put forward a method to improve HS amount by studying the formation regularity of HS. Five precursors have been detected and few researches combined them with bacteria to study HS formation. During composting, the polyphenols, carboxyl and amino acids concentration decreased by 75.8%, 63.2% and 68.3% on average, respectively. However, the polysaccharides, reducing sugars and HS concentration increased by 61.2%, 47.1% and 37.33% on average. Relationships between precursors and HS concentration showed that the HS formation were significantly affected (p<0.05). The key bacteria community and physical-chemical parameters which affected HS formation have also been identified by redundancy analysis. Twelve key bacteria communities have been selected, which were significantly affected by physical-chemical parameters (p<0.05). Accordingly, we proposed an adjusting method to promote HS amount during composting based on the relationship between the key bacteria communities and the precursors as well as physical-chemical parameters.

Advances and prospects in biogenic substances against plant virus: A review

Plant virus diseases, known as 'plant cancer', are the second largest plant diseases after plant fungal diseases, which have caused great damage to agricultural industry. Since now, the most direct and effective method for controlling viruses is chemotherapeutics, except for screening of anti-disease species. As the occurrence and harm of plant diseases intensify, production and consumption of pesticides have increased year by year, and greatly contributed to the fertility of agriculture, but also brought a series of problems, such as the increase of drug resistance of plant pathogens and the excessive pesticide residues. In recent years, biopesticide, as characterized by environmentally safe due to low residual, safe to non-target organism due to better specificity and not as susceptible to produce drug resistance due to diverse work ways, has gained more attention than ever before and exhibited great development potential. Now much progress has been made about researches on new biogenic anti-plant-virus substances. The types of active components include proteins, polysaccharides and small molecules (alkaloids, flavonoids, phenols, essential oils) from plants, proteins and polysaccharides from microorganisms, polysaccharides from algae and oligochitosan from animals. This study summarized the research advance of biogenic anti-plant-virus substances in recent years and put forward their further development in the future.

Control of dimethyl sulfide and dimethyl disulfide odors during pig manure composting using nitrogen amendment

Effects of nitrogen electron acceptors on dimethyl sulfide (Me₂S) and dimethyl disulfide (Me₂SS) odor emission during composting was investigated. The chemicals and doses used included sodium nitrate (NO₃^- at 10mM, 20mM and 40mM), sodium nitrite (NO₂^- at 10mM, 20mM and 40mM) and sodium nitrite (10mM, 20mM and 40mM) with hexaammonium heptamolybdate tetrahydrate (HHT). The results showed that the addition of these chemicals restricted the emission of Me₂S and Me₂SS. The emission reduction effect of NO₂^- was greater than NO₃^- at the same dosage. A greater reduction was observed when HHT was also added. With 2mM HHT+40mM NO₂^- addition, the emission of Me₂S and Me₂SS was reduced by 92.3% and 82.3%, respectively. Comparison of compost maturity indices for treated and untreated composts indicated that none of the additives adversely affected compost quality. These results indicate that nitrogen chemical addition may provide an efficient method to control sulfur odors during composting.

A regulating method for reducing nitrogen loss based on enriched ammonia-oxidizing bacteria during composting

In this study, enriched ammonia-oxidizing bacteria (AOB) were acquired by domesticated cultivation, followed by inoculation into the co-composting of rice straw and chicken manure. The effect of inoculation on nitrogen loss, the succession of bacterial community and the correlation between the key bacteria and environmental factors were investigated. The results showed that inoculation could reduce ammonia emission and nitrogen loss by transforming ammonium into nitrite. Inoculation also increased the amount and abundance of bacterial community. Redundancy analysis showed that indigenous and exogenous bacteria in inoculation group, compared with those in control group, were positively correlated with nitrite but negatively correlated with ammonium, demonstrating that the former contributed to the lower ammonia emission and nitrogen loss. Based on these results, the application of enriched AOB was proposed as a new method of resource recycle and improvement of composting technology.

Effects of copper on the abundance and diversity of ammonia oxidizers during dairy cattle manure composting

This study investigated the effects of adding Cu(II) at two exposure levels (50 and 500mgkg^-1, i.e., Cu50 and Cu500 treatments, respectively) on the activity of ammonia-oxidizing microorganisms during dairy cattle manure composting. The results showed that the pH, NH₄⁺-N, NO₃^--N, and potential ammonia oxidation values were inhibited significantly by the addition of Cu(II). Furthermore, the abundances of the ammonia-oxidizing archaea (AOA) amoA gene and ammonia-oxidizing bacteria (AOB) amoA gene were determined by quantitative PCR, and their compositions were evaluated by denaturing gradient gel electrophoresis (DGGE). AOA was the dominant ammonia oxidizing microorganism, of which the abundance was much higher than AOB during composting. Cu50 and Cu500 had significant inhibitory effects on the abundance of the amoA gene. The DGGE profile and statistical analysis showed that Cu(II) changed the AOA and AOB community structure and diversity, where Nitrosomonas and Crenarchaeota dominated throughout the composting process.

Effect of actinobacteria agent inoculation methods on cellulose degradation during composting based on redundancy analysis

In this study, actinobacteria agent including Streptomyces sp. and Micromonospora sp. were inoculated during chicken manure composting by different inoculation methods. The effect of different treatments on cellulose degradation and the relationship between inoculants and indigenous actinobacteria were investigated during composting. The results showed that inoculation in different stages of composting all improved the actinobacteria community diversity particularly in the cooling stage of composting (M3). Moreover, inoculation could distinctly accelerate the degradation of organic matters (OM) especially celluloses. Redundancy analysis indicated that the correlation between indigenous actinobacteria and degradation of OM and cellulose were regulated by inoculants and there were significant differences between different inoculation methods. Furthermore, synergy between indigenous actinobacteria and inoculants for degradation of OM and cellulose in M3 was better than other treatments. Conclusively, we suggested an inoculation method to regulate the indigenous actinobacteria based on the relationship between inoculants and indigenous actinobacteria and degradation content.

Successions and diversity of humic-reducing microorganisms and their association with physical-chemical parameters during composting

Humic-reducing microorganisms (HRMs) could utilize humic substances (HS) as terminal electron mediator to promote the biodegradation of recalcitrant pollutants. However, the dynamics of HRMs during composting has not been explored. Here, high throughput sequencing technology was applied to investigate the patterns of HRMs during three composting systems. A total of 30 main genera of HRMs were identified in three composts, with Proteobacteria being the largest phylum. HRMs were detected with increased diversity and abundance and distinct patterns during composting, which were significantly associated with dissolved organic carbon, dissolved organic nitrogen and germination index. Regulating key physical-chemical parameters is a process control of HRMs community composition, thus promoting the redox capability of the compost. The redox capability of HRMs were strengthened during composting, suggesting that HRMs of the compost may play an important role on pollutant degradation of the compost or when they are applied to the contaminated soils.

The evolution of water extractable organic matter and its association with microbial community dynamics during municipal solid waste composting

The humification of water extractable organic matter (WEOM) by microorganisms is widely used for assessing compost maturity and quality. However, the effect of bacterial and fungal community dynamics on humification of WEOM was not yet explored fully. Here, we used canonical correspondence analysis (CCA) and redundancy analysis (RDA) to investigate the link between bacterial and fungal community dynamics and humification process of WEOM, respectively. Results showed that water-soluble carbon (WSC), humification degree, molecule weight and abundance of aromatic carbon were significantly related to bacterial community (p<0.05), while the protein-like materials were statistically influenced by fungal community (p<0.05). Both bacterial and fungal communities significantly affected the abundance of oxygen-containing functional groups and humic-like materials (p<0.05). These humification parameters were most likely to be influenced by some of bacterial and fungal species at different composting stages. Lactobacillus, Aspergillus fumigatus and Galactomyces geotrichum can enhance the degradation of WSC and protein-like materials at the early composting. Bacteroidetes and Firmicutes could promote the increase of aromatic carbon, oxygen-containing functional groups, humification degree and molecular weight of WEOM during the initial fermentation stage. Cladosporium herbarum and Chaetomium globosum could be the dominant controllers at the second fermentation for acceleratingthe formation of oxygen-containing functional groups and humic-like materials of WEOM, respectively. Our results suggested that regulation for the dynamics of these special bacterial and fungal species at different composting stages might be a potential way to accelerate humification of municipal solid waste composting.

A regulating method for the distribution of phosphorus fractions based on environmental parameters related to the key phosphate-solubilizing bacteria during composting

This study was conducted to assess the abundance, incidence and diversity of the culturable phosphate-solubilizing bacteria (PSB) community during different organic wastes composting. The key PSB affecting different phosphorus (P) fractions and their relationship with environmental variables were analyzed by redundancy analysis (RDA). The results showed that there were distinct differences in amounts, incidence and community composition of PSB for the composts from different sources. Regression analysis demonstrated significant corrections between the density and incidence of PSB and pH, temperature, OM and DOC/DON. Most of culturable PSB showed high percentages of identity with the phyla of Firmicutes and Proteobacteria. There were thirteen key PSB correlated closely (p<0.05) with different P fractions variation. Conclusively, we suggested a process control method to regulate the distribution of P fractions during composting based on the relationship between the key PSB and P fractions as well as environmental parameters.

Application of compost for effective bioremediation of organic contaminants and pollutants in soil

Soils contaminated with hazardous chemicals worldwide are awaiting remediation activities; bioremediation is often considered as a cost-effective remediation approach. Potential bioapproaches are biostimulation, e.g. by addition of nutrients, fertiliser and organic substrates, and bioaugmentation by addition of compound-degrading microbes or of organic amendments containing active microorganisms, e.g. activated sludge or compost. In most contaminated soils, the abundance of the intrinsic metabolic potential is too low to be improved by biostimulation alone, since the physical and chemical conditions in these soils are not conducive to biodegradation. In the last few decades, compost or farmyard manure addition as well as composting with various organic supplements have been found to be very efficient for soil bioremediation. In the present minireview, we provide an overview of the composting and compost addition approaches as 'stimulants' of natural attenuation. Laboratory degradation experiments are often biased either by not considering the abiotic factors or by focusing solely on the elimination of the chemicals without taking the biotic factors and processes into account. Therefore, we first systemise the concepts of composting and compost addition, then summarise the relevant physical, chemical and biotic factors and mechanisms for improved contaminant degradation triggered by compost addition. These factors and mechanisms are of particular interest, since they are more relevant and easier to determine than the composition of the degrading community, which is also addressed in this review. Due to the mostly empirical knowledge and the nonstandardised biowaste or compost materials, the field use of these approaches is highly challenging, but also promising. Based on the huge metabolic diversity of microorganisms developing during the composting processes, a highly complex metabolic diversity is established as a 'metabolic memory' within developing and mature compost materials. Compost addition can thus be considered as a 'super-bioaugmentation' with a complex natural mixture of degrading microorganisms, combined with a 'biostimulation' by nutrient containing readily to hardly degradable organic substrates. It also improves the abiotic soil conditions, thus enhancing microbial activity in general. Finally, this minireview also aims at guiding potential users towards full exploitation of the potentials of this approach.