How discontinuous feeding increases functional stability in anaerobic digestion

Background Demand-driven biogas production could play an important role for the future sustainable energy supply. However, feeding a biogas reactor according to energy demand might lead to organic overloading and thereby to process failures. To minimize this risk, digesters need to be actively steered towards containing more robust microbial communities. This study focuses on acetogenesis and methanogenesis as the most vulnerable process steps. We fed lab-scale anaerobic digesters with volatile fatty acids under various feeding regimes and disturbances. The resulting microbial communities were analyzed on DNA and RNA level by terminal restriction fragment length polymorphism of the mcrA gene, by 16S rRNA gene amplicon sequencing, and by a [2-13C]-acetate assay. A modified Anaerobic Digestion Model 1 (ADM1) that distinguishes between the acetoclastic methanogens Methanosaeta and Methanosarcina was developed and fitted using experimental abiotic and biotic process parameters. The composition of the microbial community determined the AD functional resilience against organic overloadings in our experiments. In particular, communities enriched in Methanosarcina showed higher process stability. These microorganisms can be purposefully enriched by discontinuous feeding. A model was developed which enables to derive the necessary feeding regime for a more robust community enriched with Methanosarcina.