Selection, composition, and validation of standard inoculum for anaerobic digestion assays

The inoculum is the initial source of microorganisms for the anaerobic digestion (AD). An active inoculum aids the success of organic matter degradation experiments. Enrichment and acclimation strategies have been studied in search of more efficient tests. The present study aimed to compose an active anaerobic mesophilic inoculum in the laboratory for test standardization. For this purpose, inoculums from different sources available in the study region, such as digested cattle manure (DCM), digested sewage sludge (DSS), digested food waste (DFW), digested swine manure (DSM), fresh cattle manure (FCM), cattle rumen (CR) and some compositions between them were tested in Biochemical methane potential (BMP) assays with microcrystalline cellulose as reference substrate, in addition to fruit and vegetable waste (FVW). The inoculums originated from anaerobic processes showed a greater aptitude for the AD process, being the mixture of DFW, DSM and DCM (Mix 4) presented an abundance of the genus of bacteria DMER64 and Archaeas Methanosaeta, greater production of biogas for the reference substrate, and greater production of biogas and methane for FVW. The aptitude control tests demonstrated that the maintenance of the laboratory reactor with Mix 4 inoculum was efficient. It was evident that the characteristics of inoculum can vary from one collection to another, which validates the fact that the maintenance of an active anaerobic mesophilic inoculum in the laboratory is essential for carrying out AD ex-periments with standardized and reliable results.