Recognize and assessment of key host humic-reducing microorganisms of antibiotic resistance genes in different biowastes composts.

Humic-reducing microorganisms (HRMs) can utilize humic substance as terminal electron mediator promoting the bioremediation of contaminate, which is ubiquitous in composts. However, the impacts of HRMs on antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in composts and different HRMs community composition following the types of biowastes effected the spread of ARGs have not been investigated. Herein, the dynamics and mobility of ARGs and HRMs during protein-, lignocellulose- and lignin-rich composting were investigated. Result show that ARGs change significantly at the thermophilic phase, and the relative abundance of most ARGs increase during composting. Seven groups of HRMs communities are classified as primary host HRMs of ARGs, and most host HRMs groups from protein-rich composts. Conclusively, regulating methods for inhibiting ARGs spread for different composts are proposed. HRMs show a higher ARGs dissemination capacity in protein-rich composts than lignocellulose- and lignin-rich composts, but the spread of ARGs can be inhibited by regulate physicochemical parameters in protein-rich composts. In contrary, most HRMs have inhibitory effects on ARGs spread in lignocellulose- and lignin-rich composts, and those HRMs can be used as a new agent that inhibits the spread of ARGs. Our results can help in understanding the potential risk spread of ARGs by inoculating functional bacteria derived from different biowastes composts for environmental remediation, given their expected importance to developing a classification-oriented approach for composting different biowastes.

[Different Responses of Soil Dissolved Organic Matter to Different Types of Compost].

This study explored the responses of soil dissolved organic matter (DOM) to the application of different types of compost using a soil sample without compost as a control. Ultraviolet and fluorescence spectrum technology and EEM-PARAFAC was used to analyze DOM structure and driving factors in soil added with different proportion of cow dung compost (SCC), food and kitchen waste compost (SFC), and sludge compost (SCC). Compared with the control group, contents of AN, NH4+-N, DOC, and SOM in soil added with compost were significantly increased, and contents of SOM and DOC increased with the increasing of compost amount. When added compost in the same proportion, contents of AN, NO3--N, and DOC in SCC and SFC were significantly higher than those in SSC, while contents of NH4+-N and SOM were higher in SSC. The results of spectral analysis showed that the structure of conjugated benzene ring, hydrophobic component, quinone group, and chromogenic component in DOM of soil added with compost were significantly increased, the transition of unsaturated organic molecule (π→π*) was more active, the molecular weight of DOM increased, and the degree of humification was enhanced. When the amount of compost added is 5%, the influence of food and kitchen waste compost on DOM structure was greatest among three types of compost. At 10% and 20%, sludge compost had the greatest impact on DOM structure. The results of EEM-PARAFAC analysis showed that the relative content of fulvic acid-like substances with low molecular in DOM of soil added with compost was increased, while the relative content of proteoid-like substances decreased. 2D-COS analysis showed that compost affected the change order of fluorescence components in DOM. SCC and SFC were as follows:proteoid-like > fulvic acid-like > humus-like; in SSC, it was fulvic acid-like > proteoid-like > humus-like. The enhance of humification and the decrease of relative content of protein-like substances in DOM were related to increased DOC and AN, the relative content of humus-like in low molecular weight was positively correlated with the content of NO3--N, and the relative content of macromolecule fulvic acid-like was increased due to the input of SOM from compost.

[Different Responses of Soil Microbial Community Structure to Irrigation with Treated Wastewater from Domestic and Industrial Sources].

To investigate the long-term effects of irrigation with treated domestic and industrial wastewater on the microbial community structure of the soil, Illumina MiSeq high-throughput sequencing technology was applied. Groundwater irrigated soil was used as a control. The effects of soil environmental factors and their interactions on the microbial community structure were investigated. Compared with the groundwater irrigation, irrigation with treated domestic wastewater can significantly increase the contents of TOC, DOC, Eh, NH4+-N, and TP, whereas irrigation with treated industrial wastewater can increase the contents of Cd, Cr, Cu, Pb, and Zn in the soil. Irrigation with treated wastewater also increases the relative abundance of Acidobacteria and Planctomycetes, and reduces the relative abundance of Firmicutes and Tectomicrobia. The effects of treated wastewater from different sources on functional microorganisms in soil are also different; irrigation with treated domestic wastewater can increase the relative abundance of Chloroflexi and Nitrospirae, whereas irrigation with treated industrial wastewater has negative effects on the abundance of Actinobacteria. The results of db-RDA analysis show that TN, TP, DOC, and Eh are the main factors that impact the microbial communities in soils irrigated with treated domestic wastewater (P<0.05), and heavy metals are the main factors that impact the microbial communities in soils irrigated with treated industrial wastewater (P<0.05). Compared with groundwater irrigation, treated wastewater irrigation can change the correlations between soil environmental factors, which in turn affect the microbial community structure. The growth of microorganisms in soils irrigated with treated domestic wastewater is mainly controlled by the increase in the nutrients such as DOC, TN, and TP and changes in soil redox conditions. The abundance of microorganisms in soil irrigated with treated industrial wastewater is significantly correlated with the accumulation of heavy metals.

Succession and diversity of microbial communities in landfills with depths and ages and its association with dissolved organic matter and heavy metals.

Landfill is an important method for the treatment of municipal solid wastes. Microbes play a central role in the biodegradation and stabilization of organic matter during landfill; however, the succession of microbial communities in landfills and their association with organic matter still remain unclear. This study investigated the succession and diversity of microorganisms in landfill depending on different depths and ages as well as its association with dissolved organic matter (DOM) and heavy metals. The results showed that the actinobacterial diversity and richness were high compared to bacteria in young landfill cells. The diversity and richness of bacteria and actinobacterial were the highest in the middle layer in the intermediate and old landfill cells. Firmicutes, Proteobacteria, and Actinobacteria were the most dominant phyla. Firmicutes were mainly affected by the humification degree, and the aromatic and protein-like substance content of the landfill-derived DOM. The phylum Proteobacteria was greatly affected by the lipid and humic-like substances content of the landfill-derived DOM, while the distribution of Actinobacteria was regulated by both aromatic and humic-like substances. The effect of dissolved heavy metals on the microbial distribution in landfill differed for the metals Cr, Ni, Pb, Mn, Cu, Zn, and Cd. Siderophile elements (Cr, Ni, and Pb) were necessary trace elements for Proteobacteria and Actinobacteria, and promoted their growth. Oxyphilic element (Mn) was an important factor promoting the growth of Actinobacteria. However, no apparent relationship was found between sulfurophile elements (Cu, Zn, and Cd) and microorganisms.

[Degradation of Pentachlorophenol by Fulvic Acid in a Municipal Solid Waste Landfill].

The structural composition and functional group changes in fulvic acid (FA) at various landfills were studied using ultraviolet and infrared spectroscopy. The electron transfer ability of FA and its ability to degrade pentachlorophenol (PCP) were also studied considering the various landfills. The results showed that the use of MR-1 as an electron donor and the simultaneous addition of fulvic acid in different stages as an electron shuttle can significantly increase the degradation rate of PCP, leading it beyond 80%. Due to the different redox properties of fulvic acid at the different landfill stages, the degradation of PCP has different reduction conversion abilities. Landfill fulvic acid is able to reduce and transform PCP because of its electron transfer ability. These functions are all conducive to promoting PCP reductive dechlorination.

Heterogeneity of the electron exchange capacity of kitchen waste compost-derived humic acids based on fluorescence components.

Composting is widely used for recycling of kitchen waste to improve soil properties, which is mainly attributed to the nutrient and structural functions of compost-derived humic acids (HAs). However, the redox properties of compost-derived HAs are not fully explored. Here, a unique framework is employed to investigate the electron exchange capacity (EEC) of HAs during kitchen waste composting. Most components of compost-derived HAs hold EEC, but nearly two-thirds of them are found to be easily destroyed by Shewanella oneidensis MR-1 and thus result in an EEC lower than the electron - donating capacity in compost-derived HAs. Fortunately, a refractory component also existed within compost-derived HAs and could serve as a stable and effective electron shuttle to promote the MR-1 involved in Fe(III) reduction, and its EEC was significantly correlated with the aromaticity and the amount of quinones. Nevertheless, with the increase of composting time, the EEC of the refractory component did not show an increasing trend. These results implied that there was an optimal composting time to maximize the production of HAs with more refractory and redox molecules. Recognition of the heterogeneity of EEC of the compost-derived HAs enables an efficient utilization of the composts for a variety of environmental applications. Graphical abstract Microbial reduction of compost-derived HAs.

Insight into the composition and degradation potential of dissolved organic matter with different hydrophobicity in landfill leachates.

Dissolved organic matter (DOM) isolated from the leachates with different landfill ages was fractionated into hydrophobic acid (HOA), hydrophobic neutral (HON), hydrophobic base (HOB) fractions and hydrophilic matter (HIM) based on hydrophobicity, and the composition and degradation potential of the bulk DOM and its fractions were investigated by excitation-emission matrix fluorescence spectra coupled with parallel factor analysis. Results showed that the bulk DOM comprised fulvic-, humic-, tryptophan- and tyrosine-like substances, as well as component C1, whose composition and origin was unidentified. Landfill process increased the content of component C1, fulvic- and humic-like matter. The HON fractions comprised primarily component C1 and tyrosine-like matter. The HOA, HOB and HIM fractions isolated from the young leachates consisted mainly of tryptophan- and tyrosine-like substances. As to the intermediate and old leachates, the HOA and HOB fractions comprised mainly component C1, while the HIM comprised mainly fulvic-like matter. The HIM showed the most resistant against biodegradation among the four fractions, and was the main component of leachate treatment. Advanced oxidation and/or membrane treatment are recommended to remove the HIM fraction due to its hydrophilic and stable characteristics.

[Composition and Evolution Characteristics of Dissolved Organic Matter During Composting Process].

According to the fraction method presented by Leenheer, dissolved organic matter (DOM) extracted from chicken manure with different composting time was fractionated into five groups [i. e., hydrophobic acid (HOA), hydrophobic base (HOB), hydrophobic neutral (HON) fractions, acid-insoluble (AIM) and hydrophilic matter (HIM)] using the XAD-8 resin based on its polarity and electric charge characteristics. The composition and structures of these fractions were investigated by elemental analysis, FTIR and 1H-NMR spectra. The results showed that the HIM and HOA fractions accounted for 32%-44% and 35%-47% of DOM, respectively, during the composting process, while the sum of the fractions HOB, AIM and HON was responsible for less than 25% of DOM. The HIM content decreased while the hydrophobic component increased after composting. The elemental analysis indicated that, during the composting process, the N, C, S content of all five fractions increased, the H/C ratio decreased, but the humification degree increased; The result from 1H-NMR analysis showed that the HIM had low alkyl chain, short branched chain, high branches and carbohydrate structure, which was opposed to the HON fraction. The composition of AIM was similar to that of humic acids, while the HOB was rich in nitrogen-containing compounds. The result from the FTIR analysis showed that the HOA and HOB fractions were rich in abundant carboxyl, ester group and hydroxyl functional group. Besides the above functional groups, the AIM and HIM were rich in benzene groups. The HON fraction was rich in aliphatic functional group except for the abovementioned functional groups. The aliphatic functional group was degraded and the benzene functional group after composting.

[Spectral Characteristic of Dissolved Organic Matter in Xiaohe River, Hebei].

The spectral characteristic of dissolved organic matter (DOM) in Xiaohe River, Hebei, was investigated by fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, and basic chemical water quality indicators. The data was then statistical analyzed using principal component analysis and correlation analysis method. The result based on 3D excitation-emission matrix fluorescence spectroscopy showed that DOM in Xiaohe River contained both protein-like and humus-like components. DOM and N-containing compounds were obviously correlated with COD, especially between NH4+ -N and humic-like component, indicating that COD of water in Xiaohe River can be reduced by removing NH4+ -N and DOM, which could be good indicators for monitoring water quality in the future. The relative content of protein-like component reduces gradually along the downstream, while that of humic-like component showed an increasing trend. DOM in samples S1 and S2 was mainly consisted of humic-like components with larger molecular weight and higher aromaticity, while that in samples S3 and S6 was mainly consisted of protein-like components with smaller molecular weight, lower aromaticity, which are easier to be degraded. Therefore, in order to enhance the remove of refractory humic-like substances, sewage treatment plants of S1 and S2 or improved membrane treatment equipment with better removal effect of macromolecules should be provide. On the other hand, the anaerobic and aerobic biological treatment processes should be optimized in S3 and S6, so as to better remove these degradable protein-like substances.

Effect of inoculation methods on the composting efficiency of municipal solid wastes.

Four types of inoculation methods were studied during the composting of municipal solid wastes and dry grass (MSWG). The methods included a control group as well as initial-stage, two-stage, and multi-stage inoculations. Fulvic acids were extracted from the composting materials and characterized by spectroscopic techniques. The results showed that inoculation of microbes in MSWG enhanced the biodegradation of aliphatics, proteins, and polysaccharides. The inoculation also increased the molecular weight, humic- and fulvic-like compound content, as well as humification degree of the composting products. The inoculation of microbes in MSWG significantly improved composting process and efficiency. The improvement efficiency was in the order of initial-stage < two-stage < multi-stage inoculations. Inoculation of microbes based on composting organic matter composition and temperature enhanced composting efficiency.

[Effects of multi-stage strengthening inoculation on bacterial community diversity during composting].

Effects of multi-stage strengthening inoculation on bacterial community diversity were analyzed using PCR-DGGE method in municipal solid waste composting combined with Cluster analysis and changes of Shannon-Weaver index, and the changes of lignocellulose's degradation rate were also detected during the process. The results showed that Multi-stage inoculation of composting can improve the temperature of cooling and the secondary fermentation period. And the hemicellulose, cellulose and lignin degradation rate increased by 7.19%, 10.89% and 8.98% compared to general inoculation composting. The analysis of bacterial community diversity indicated that the diversity index of the two inoculation showed significant differences, the microbial inoculation could live well in the pile. It could avoid competition between different inoculated agents and competition between inoculated and indigenous microorganisms, and could improve bacterial community diversity during composting especially for maturity stage. It could speed up the composting process of stabilization.