Feeding pattern variation induces functional stability in anaerobic digestion

Anaerobic digestion (AD) is an environmental key technology and plays a central role in the future bio-based economy by converting a wide diversity of organic downstream products into biogas. In order to achieve functional stability, a minimal microbial community diversity is required. Moreover, this microbial community should also have a certain “elasticity”, i.e. the ability to rapidly adapt to sub-optimal conditions or stress. In this study it was evaluated whether a higher degree of functional stability could be achieved by changing the feeding pattern, which can change the evenness, dynamics and richness of the bacterial community. The first reactor (CSTRstable) was fed on daily basis, whereas the second reactor (CSTRdynamic) was fed every two days. Both reactors were operated at an organic loading rate of 1 g COD L-1 d-1 and a hydraulic retention time of 20 days. Average biogas production was 0.30L CH4 L-1 d-1 in both reactors, although daily variation was up to four times higher in the CSTRdynamic compared to the CSTRstable during the first 50 days. Bacterial analysis revealed that this CSTRdynamic had a two times higher degree of bacterial community dynamics. The CSTRdynamic also appeared to be more tolerant to an organic shock load of 8 g COD L-1 and high levels of ammonium, up to 8000 mg TAN L-1. These results suggest that the regular application of a limited pulse of organic material and/or a variation in the substrate composition might promote a higher degree of functional stability in the anaerobic digester