Phosphate rock reduces the bioavailability of heavy metals by influencing the bacterial communities during aerobic composting

Available information on the microbial mechanisms associated with heavy metal(HM)passivation during co-composting amended with phosphate rock(PR)remains limited.Thus,this study investigated the dynamic changes in bacterial communities and HM-fractions(Zn,Cu,Cd,Cr and Pb)during swine manure composting with maize straw,and ascertained the bacterial influence on HM-passivation.The results demonstrated that the addition of PR improved HM-passivation,especially for Zn and Cd,with their bioavailability factors(BFs)reduced by 247.41 and 176.25%,respectively.As for bacterial communities,the proportion of Firmicutes decreased,while the proportions of Proteobacteria,Bacteroidetes,DeinococcusThermus and Gemmatimonadetes increased in all treatments.PR significantly changed the primary bacterial phyla in the thermophilic phase.Bacteroidetes were the main bacterial component controlling the passivation of Zn,Cu and Cr,while Deinococcus-Thermus mainly regulated the mobility of Zn and Pb,and Proteobacteria only dominated the transformation among Cd-fractions.These results may provide a reference for the use of HM-passivation techniques during composting.

Influence of dissolved organic matter on methylmercury transformation during aerobic composting of municipal sewage sludge under different C/N ratios

Current knowledge about the transformation of total mercury and methylmercury(Me Hg) in aerobic composting process is limited. In this study, the composition and transformation of mercury and dissovled organic matter(DOM) in aerobic composting process of municipal sewage sludge were were comprehensively characterized, and the differences among the three C/N ratio(20, 26 and 30) were investigated. The main form of mercury in C/N 20 and 26 was organo-chelated Hg(F3, 46%-60%);while the main form of mercury in C/N 30 was mercuric sulfide(F5, 64%-70%). The main component of DOM in C/N 20 and 26 were tyrosine-like substance(C1, 53%-76%) while the main fractions in C/N 30 were tyrosine-like substance(C1, 28%-37%) and fulvic-like substance(C2, 17%-39%). The mercury and DOM varied significantly during the 9 days composting process. Compared to C/N 20 and 26, C/N 30 produced the less Me Hg after aerobic composting process, with values of 658%(C/N 20), 1400%(C/N 26) and 139%(C/N 30) of the initial, respectively. Meanwhile, C/N 30 produced the best compost showed greater degree of DOM molecular condensation and humification. Hg fraction had been altered by DOM, as indicated by a significant correlation between mercury species and DOM components. Notably, C/N 30 should be used as an appropriate C/N ratio to control the methylation processes of mercury and degration of DOM.

Environmental effects and risk control of antibiotic resistance genes in the organic solid waste aerobic composting system: A review

Antibiotic resistance genes(ARGs)have been diffusely detected in several kinds of organic solid waste,such as livestock manure,sludge,antibiotic fermentation residues,and food waste,thus attracting great attention.Aerobic composting,which is an effective,harmless treatment method for organic solid waste to promote recycling,has been identified to also aid in ARG reduction.However,the effect of composting in removing ARGs from organic solid waste has recently become controversial.Thus,this article summarizes and reviews the research on ARGs in relation to composting in the past 5 years.ARGs in organic solid waste could spread in different environmental media,including soil and the atmosphere,which could widen environmental risks.However,the conventional composting technology had limited effect on ARGs removal from organic solid waste.Improved composting processes,such as hyperthermophilic temperature composting,could effectively remove ARGs,and the HGT of ARGs and the microbial communities are identified as vital influencing factors.Currently,during the composting process,ARGs were mainly affected by three response pathways,(Ⅰ)“Microenvironment-ARGs”;(Ⅱ)“Microenvironment-microorganisms-ARGs”;(Ⅲ)“Microorganisms-horizontal gene transfer-ARGs”,respectively.Response pathway Ⅱ had been studied the most which was believed that microbial community was an important factor affecting ARGs.In response pathway Ⅲ,mainly believed that MGEs played an important role and paid less attention to eARGs.Further research on the role and impact of eARGs in ARGs may be considered in the future.It aims to provide support for further research on environmental risk control of ARGs in organic solid waste.

Succession of bacterial community during composting:dissimilarity between compost mixture and biochar additive

Previous research showed that biochar addition facilitated composting and elevated nutrient retention.However,few of these studies explored bacterial structure and abundance in the compost mixture and biochar additive.Thus,this study aims to distinguish bacterial communities in both compost and bamboo biochar(BB)additive.Results indicated that the dynamics of nutrient contents in compost and BB samples were in a similar pattern,although there were lower levels of nutrients and metals(i.e.,Cu and Zn)in BB additives.The total number of operational taxonomic units(OTUs)in both compost and BB additives peaked on day 7 and then gradually reduced during composting.There was more abundance of bacteria in compost,whereas the diversity of bacteria was more in BB additives.Furthermore,the dominant bacteria in compost and BB samples were distinct at the different stages of composting.The Firmicutes steadily decreased in compost samples(from 34.78%to 7.65%),while it was the dominant phylum in BB additives during the whole composting period.Furthermore,Ruminofilibacter,Pseudoxanthomonas,and Actinomadura were the most abundant genera in compost samples than Pseudoxanthomonas,Azoarcus,and Paenibacillus in BB additives at the final stage of composting.Results from this study could provide a theoretical reference for the sound performance of biochar-added composting.

Life cycle assessment on the environmental impacts of different pig manure management techniques

The management of livestock waste is an effective way to achieve emission reduction and carbon fixation in agriculture and rural areas.At present,aerobic composting and anaerobic fermentation are widely used in livestock waste treatment technology.In this study,pig manure management was taken as an example,a comprehensive environmental load index was constructed to quantitatively evaluate the environmental impacts of global warming,environmental acidification,eutrophication,and photochemical ozone synthesis during aerobic composting and anaerobic fermentation based on the life cycle assessment.The results showed that the potential values of aerobic composting and anaerobic fermentation were similar,and the order was global warming,environmental acidification,eutrophication,and photochemical ozone synthesis.Anaerobic fermentation contributed more to global warming,while aerobic composting contributed more to environmental acidification,eutrophication,and photochemical ozone synthesis.In addition,the environmental load index of aerobic composting was significantly higher than that of anaerobic fermentation.There were certainly regional differences in the environmental load index,and the environmental impact effect of anaerobic fermentation was low and more environmentally friendly.These findings provided a technical basis for livestock manure management in different regions of China,which was conducive to promoting animal husbandry emission reduction and carbon sequestration.