Ammonia assimilation is key for the preservation of nitrogen during industrial-scale composting of chicken manure.

Nitrogen loss from compost is a serious concern, causing severe environmental pollution. The NH4+-N content reflects the release of NH3. However, the nitrogen conversion pathway that has the greatest impact on NH4+-N content is still unclear. This study attempted to explore the key pathways, core functional microorganisms, and mechanisms involved in the transformation of ammonia nitrogen during composting. KEGG (Kyoto Encyclopedia of Genes and Genomes) metabolic pathways revealed that ammonia assimilation was dominated by the glutamate dehydrogenase (GDH) pathway (53.4%), which is crucial for nitrogen preservation. The combined analysis of KEGG, NR species annotation, and co-occurrence network identified 20 easy-to-regulate obligate core nitrogen-transforming functional microorganisms, including 18 ammonia-assimilating bacteria. Furthermore, the effects of environmental parameters on the obligate core functional microorganisms were investigated. The present study results provided a theoretical basis for the utilization of ten ammonia-assimilating bacteria, such as Paenibacillus, Erysipelatoclostridium, and Defluviimonas to improve the quality of compost.

Effect of hydrochar on antibiotic-resistance genes and relevant mechanisms during chicken manure composting.

The reduction of enhanced antibiotic resistance genes (ARGs) in compost is important to mitigate the risk of ARG transmission in agricultural production. Hydrochar is used in many applications as a functional carbon material with adsorption and catalytic properties. This study investigated the effects of hydrochar addition on bacterial communities, mobile genetic elements (MGEs), and ARGs in chicken manure composting. The addition of 2%, 5%, and 10% hydrochar (dry weight) reduced the total numbers of target ARGs and MGEs in the compost products by 40.13-55.33% and 23.63-37.23%, respectively. Hydrochar changed the succession of the bacterial population during composting, lowering the abundance of potential pathogens and promoting microbial activity in amino acid and carbohydrate metabolism. A significant possible microbial host for ARGs was found to be Firmicutes. Hydrochar was found to affect the host microorganisms and MGEs directly by altering environmental factors that indirectly impacted the ARG profiles, as shown by partial least squares pathway modeling analysis. In conclusion, the addition of hydrochar to compost is a simple and effective method to promote the removal of ARGs.

Response of electron transfer capacity of humic substances to soil microenvironment.

The humic substances (HS) - mediated electron transfer process is of great significance to the reduction and degradation of pollutants and the improvement of soil quality. Different soil conditions lead to different characteristics of HS, resulting in differences in the electron transfer capacity (ETC) of HS. It is unclear how the environmental conditions in soil affect the ETC by affecting on HS. In this study, the response relationship of soil microenvironment, HS and ETC has been studied. The results show that the ETC follows the descending order of: Langshan > Nanchang > Anqing > Beijing > Guilin. There were significant differences in ETC in soil HS in different regions. There were significant differences in electron-donating capacity (EDC) in soil HS in different regions and depths. EDC in soil was higher than electron-accepting capacity (EAC), and on average, are 22.4 times higher than the EAC. The HS components of soils in different regions are different. The most significant differences were in tyrosine-like substances and soluble microbial by-products (SMPs). The five components of the soil HS from Langshan were the most different from those in other regions. There were differences in SMPs and humic-like substances in soils of different depths in Anqing and Guilin. ETC can be affected by the composition of HS components in different regions. The composition of HS at different soil depths in the same regions had little effect on ETC. SMPs can promote ETC and EDC, and tyrosine-like substance can promote EDC. Moisture content, pH and TOC are the main factors affecting the composition of HS components. This results can provide a research basis for the sustainable and safe utilization of agricultural soil.

Fate of antibiotic resistance genes in industrial-scale rapid composting of pharmaceutical fermentation residue: The role implications of microbial community structure and mobile genetic elements.

Composting is an effective technology to recycle organic solid waste as a green resource. However, pharmaceutical fermentation residue (PFR) contains a variety of pollutants, such as residual drug and antibiotic resistance genes (ARGs), which limits the green cycle of using PFR as a resource. To promote the green recycling of PFR, this study evaluated the characteristics of abundance and the response relationship of ARGs during the process of rapid composting. Different rapid composting samples were collected, and DNA was extracted from each sample. The absolute abundance of ARGs was quantified using quantitative PCR, and the microbial community structure was identified using high-throughput sequencing. The results showed that ermB, ermF, tetM and tetQ were reduced by 89.55%, 15.10%, 89.55%, and 82.30% respectively, and only sul2 increased by approximately 5-fold. Mobile genetic elements (MGEs) directly affected the changes in abundance of ARGs. As typical MGEs, intl1 and intl2 decreased by 3.40% and 54.32%, respectively. Potential host microorganisms important factors that affected ARGs and MGEs. A network analysis indicated that the potential host microorganisms were primarily distributed in Firmicutes and Proteobacteria at the phylum level. The pH and content of water-extractable sulfur were physicochemical parameters that substantially affected the abundance of potential host microorganisms through redundancy analysis. Industrial-scale rapid composting could reduce the number of ARGs and shorten the composting cycle, which merits its popularization and application.

The maturity period is the main stage of antibiotic resistance genes reduction in aerobic composting process of swine manure in sub-scale farms.

This study was focused on the changes of antibiotic resistance genes (ARGs) and their potential host bacteria during the swine manure composting on sub-scale farms. Eight target ARGs increased 427% on average, with a trend of increase at early stage and decrease at later stage, and the main reduction stage appeared in maturity stage. The abundance of ARGs was mainly affected by the community succession of potential host bacteria. Composting could reduce the abundance of potential host bacteria of ARGs as well as pathogens such as Pseudomonas, and reduce the environmental risks of swine manure. N/C and S levels had a positive effect on the potential host of most ARGs. Prolonging the maturity period would inhibit the growth of potential host bacteria of ARGs during composting, therefore inhibiting the transmission of ARGs.

Mobile genetic elements in potential host microorganisms are the key hindrance for the removal of antibiotic resistance genes in industrial-scale composting with municipal solid waste.

During the municipal solid waste (MSW) composting, antibiotic resistance genes (ARGs) could be one of the concerns to hinder the application of MSW composting. However, the understanding of enrichment and dissemination of ARGs during the industrial-scale composting is still not clear. Hence, this study aimed to investigate the ARG distributions at different stages in an industrial-scale MSW composting plant. Seven target ARGs and four target mobile genetic elements (MGEs) and bacterial communities were investigated. The abundances of ARGs and MGEs increased during two aerobic thermophilic stages, but they decreased in most ARGs and MGEs after composting. Network analysis showed that potential host bacteria of ARGs were mainly Firmicutes and Actinobacteria. The reduction of potential host bacteria was important to remove ARGs. MGEs were an important factor hindering ARG removal. Water-extractable S and pH were two main physicochemical factors in the changes of microbial community and the abundance of ARGs.

A review on occurrence and risk of polycyclic aromatic hydrocarbons (PAHs) in lakes of China.

Polycyclic aromatic hydrocarbons (PAHs) residues have attracted attention worldwide. This study summarizes the current levels of PAH exposure in the water environments of lakes. In addition, the risk levels from individual PAHs and ΣPAHs in the water environments of lakes in China were evaluated by incremental lifetime cancer risk (ILCR) assessment, the toxic equivalent concentration (TEQBaP), the risk quotient (RQ), the effects range-low (ERL) and the effects range-median (ERM). The results showed that the concentrations of ∑PAHs in water and sediment ranged from 4.0 to 12,970.8 ng L-1 and 6.52 to 7935.21 ng g-1, respectively, and the highest concentrations of individual PAHs were of naphthalene (Nap) (6525 ng L-1), followed by indeno(1,2,3­cd)pyrene (IcdP) (3452.6 ng g-1). Concentrations in the Great Lakes region in China showed spatial difference, with the Qinghai-Tibet Plateau Lakes District and Mongolia-Xinjiang Lakes District being less polluted. However, the pollution level of PAHs in lakes is relatively high at the global scale. The ecological risk assessment found a moderate level of ∑PAHs in water, but benz(a)anthracene (BaA) and phenanthrene (Phe) had high RQ values, which might pose a significant risk to aquatic organisms in lakes. Although the contents of ∑PAHs in sediments are low, most individual PAHs pose potential risks, especially acenaphthene (Ace), fluorene (Flu) and dibenz(a,h)anthracene (DahA). This study revealed the pollution levels of PAHs across China and provided a scientific basis for PAH pollution control and environmental protection.

Responses of the electron transfer capacity of soil humic substances to agricultural land-use types.

Humic substances (HS) are redox-active organic compounds that constitute a major fraction of natural organic matter in soils. The electron transfer capacity (ETC) of soil HS is mainly dependent on the type and abundance of redox-active functional groups in their structure. It is unclear whether or not agricultural land-use types can affect the ETC of HS in soils. In the present study, we evaluate the responses of ETCs of soil humic acids (HA) and fulvic acids (FA) to different agricultural land-use types. Our results show that both HA and FA of paddy soil showed the highest ETCs, followed by tomato soil, celery cabbage soil, grapevine soil, and myrica rubra soil, respectively. Agricultural land-use types could affect the transformation and decomposition of HS in soils, and thus further change the intrinsic chemical structures associated with ETC. Consequently, the ETC of soil HS exerts a significant difference among different agricultural land-use types. The results of this study could give insight into the roles of HS redox properties on the transport, fate, and redox conversion of organic and inorganic pollutants in different agricultural soils.