Microbiologic assessment of accelerated solid-state fermentation of agricultural organic wastes

Livestock and poultry wastes, when effectively managed, become feedstock for organic fertiliser production. Researchers from the All-Russian Research Institute of Reclaimed Lands, the branch of Federal Research Center “V.V. Dokuchaev Soil Science Institute”, proposed an accelerated regimen of cattle manure solid-phase fermentation with peat: 48 h at 37 °C, then 48 h at 60 °C and 24 h at 37 °C, terminating with nat-ural cooling of the fermented mass. A distinctive feature of the proposed accelerated fermentation is maintenance of set-point temperatures. The aim of the work is to perform a microbiological evaluation of the process of accelerated solid-phase fermentation. An experiment was carried out in a 1.75 dm3 laboratory fermenter. During the fermentation, we studied the number of microorganisms, which use organic and mineral nitrogen forms, using the limiting dilution method, as well as the species membership by mass spectrometry. The experimental findings showed that the temperature regime of the main fermentation steps yielded the maximum number of mesophilic and thermophilic nitrogen-transforming microorganisms. Their active growth caused the intensive transformation of the fermented mixture, as evidenced by mesophilic and thermophilic mineralisation coefficients. At the end of the process, the linear mineralisation coefficients were used to assess the completion of the fermentation product transformation and stabilisation. The fermentation product comprised a high number of nitrogen-transforming microorganisms (on average, 3.5±0.3•108 COE/g on a dry weight basis). The determination of the microbiota species membership in the fermented mass and the final product confirmed that the process temperature regime ensured the elimination of the sanitary-indicatory microorganisms present in the original mixture (E. coli, Citrobacter, Proteus). In addition, during pasteurisation, this regime led to the active development of non-pathogenic Bacillus bacteria (B. megaterium, B. subtilis, B. licheniformic, B. pumilus and B. altitudinis). The fermentation product is recommended for use as an environmentally safe organic fertiliser based on the microbiological evaluation.