Abstract
BackgroundDuring strategic planning of a biogas plant, the local availability of resources for start-up and operation should be taken into consideration for a cost-efficient process. Because most bioethanol/sugar industries in Brazil are located in remote areas, the use of fresh cattle manure from local farms could be a solution for the inoculation of the biogas process. This study investigated the diversity and dynamics of bacterial and archaeal communities and the performance of biogas reactors inoculated with manure and a mixed inoculum from different biogas reactors as for a controlled start-up until steady state.ResultsLaboratory-scale biogas reactors were fed semi-continuously with sugarcane filter cake alone (mono-digestion) or together with bagasse (co-digestion). At the initial start-up, the reactors inoculated with the mixed inoculum displayed a less diverse taxonomic composition, but with higher presence of significant abundances compared to reactors inoculated with manure. However, in the final steady state, the communities of the differently inoculated reactors were very similarly characterized by predominance of the methanogenic genera Methanosarcina and Methanobacterium, the bacterial families Bacteroidaceae, Prevotellaceae and Porphyromonadaceae (phylum Bacteroidetes) and Synergistaceae (phylum Synergistetes). In the mono-digestion reactors, the methanogenic communities varied greater than in the co-digestion reactors independently of the inoculation strategy.ConclusionThe microbial communities involved in the biogas production from waste products of the Brazilian bioethanol/sugar industry were relatively similar and stable at the reactor’s steady phase independently of the inoculum source (manure or mixed inoculum). Therefore, the locally available manure can be used as inoculum for start-up of the biogas process, since it also contains the microbial resources needed. The strong fluctuation of methanogenic communities in mono-digestion reactors indicates higher risk of process instability than in co-digestion reactors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0548-4) contains supplementary material, which is available to authorized users.
Highlights
During strategic planning of a biogas plant, the local availability of resources for start-up and opera‐ tion should be taken into consideration for a cost-efficient process
Biogas reactors Six identical laboratory-scale continuously stirred tank reactors with working volumes of 3 L under mesophilic conditions (38 ± 1 °C) were established to operate three experiments in duplicate: R3.3 and R3.4 were inoculated with engineered mixed inoculum (MIX) and fed with a single substrate; R3.5 and R3.6 obtained the same inoculum, but the filter cake was co-digested with bagasse; R3.7 and R3.8 were inoculated with fresh cattle manure (FCM) and performed co-digestion to R3.5 and R.3.6
The versatile genus Methanosarcina, which contributed 32 % to the Conclusion Our results confirmed that FCM is a reliable and efficient inoculum for the co-digestion of filter cake and bagasse, since very similar methane and biogas yields were obtained under the steady-state phase, independent of the inoculation strategy
Summary
During strategic planning of a biogas plant, the local availability of resources for start-up and opera‐ tion should be taken into consideration for a cost-efficient process. Because most bioethanol/sugar industries in Brazil are located in remote areas, the use of fresh cattle manure from local farms could be a solution for the inoculation of the biogas process. In regions where biogas plants are widespread and well developed, a biogas reactor can be started with inocula from already established processes. Contrary to this scenario, in Brazil there are only very few plants applying the anaerobic digestion (AD) process to treat waste at large scale and these plants are spread across the. We have addressed the possibility of reactor inoculation with fresh cattle manure (FCM) as a locally available, potential inoculum. The microbiological background of this experiment remained to be investigated
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