Effects of inoculation of complex microbial inoculants on the process and greenhouse gas(CH4 and N2O)emissions of cattle manure aerobic composting

[Objectives] Aerobic composting of manure is an alternative strategy for stabilization,harmlessness and resourcelization of the wastes;but the composting process is usually time-consuming,and is also an important source of anthropogenic greenhouse gas (GHG) emissions.Evaluating the effects of specific inoculates on composting process of manure composting and GHG production could provide theoretical basis for developing relevant microbial products for improving composting.[Methods] In this study,an experiment involving aerobic cattle manure composing was performed,and the effects of inoculation of complex microbial inoculants (including straim of Bacillus amyloliquefaciens and Aspergillus fumigatus)on the maturity process,GHG emissions (CH4 and N2 O),and abundance of relevant functional genes,were investigated by regular measurements of physicochemical indexes,a vented chamber method,and Real-time quantitative PCR,respectively.[Results] Results indicated that inoculation of the complex microbial agents accelerated the heating process of composting,where the temperature of the inoculated pile reached 60.0 ℃ at 3 d while the control needed 9 days;also the highest temperature in treatment and control were observed to be 74.0 ℃ and 69.7 ℃,respectively.Adding of the microbial inoculants also decreased the pH and moisture of the composting as compared with those of control,while the electric conductivity(EC) of the two treatments was similar.Moreover,inoculation speeded up the decrease of C/N,as the ratio in inoculated pile decreased to 12.8 at 22 d while it was recovered as 12.5 in control pile at 32 d.CH4 and N2O emissions revealed trade-off patterns in both treatments.CH4was mainly produced at the initial stage of composting,and inoculation of the multiple strains significantly decreased its emissions as compared with control(peak of 894.9 mg·m-2· h-1 and 1 241.4 mg· m-2· h-1,respectively).Real-time PCR analysis indicated that addition of microbial agents increased mcrA abundance(referred to production of methane)but decreased pmoA abundance (involved in methane oxidation)when comparing with control.N2O emissions were observed to mainly occur at the later period of the composting and were similar within both treatments.The dynamics of population of functional genes relevant to N-cycle(amoA,nirK and nosZ)were also similar between treatment and control.[Conclusions] In conclusion,this study suggested that inoculation of the complex microbial inoculants could accelerate the heating process of manure composting,extend the thermophilic phase,and speed up the maturity,as well as decreasing the CH4emissions thus ensure harmlessness and fast maturity of the composting.This strategy could provide theoretical basis and technical assistance for management of solid wastes such as aerobic thermophilic composting.