The Role of EPS during Exposure to Inhibitors in AD Systems

Anaerobic digestion (AD) is a microorganism-driven process to produce biogas out of organic materials under oxygen-free conditions. Biogas mainly comprises of methane and carbon dioxide and poses a carbon-neutral energy source for humankind. AD of organic waste material coming from e.g., municipal solid waste or agricultural waste streams is highly desirable as this not only yields a carbon-neutral energy source but also reduces the potential for greenhouse gas emissions out of deposited wastes, reduces organic wastes in volume and weight, can sanitise waste material and produce a homogeneous digestate low in odour nuisance but high in nutrients. However, organic wastes can contain relevant concentrations of unfavourable substances like ammonia or aromatic compounds which can inhibit AD microorganisms and thus biogas production. To some extent, microorganisms can overcome unfavourable conditions by excreting extracellular polymeric substances (EPS) and organising themselves in flocs, biofilms and granules. These substances within biofilms and granules are still marginally understood and requirements and mechanisms for EPS secretion by AD microorganisms need further investigations. The project will apply a mixture of techniques including anaerobic cultivation, biochemical analyses, molecular biological approaches as well as single-cell methods and chemical imaging techniques. This combination aims at better understanding the formation and role of EPS during AD when microorganisms are exposed to certain inhibitors and to what extent multi-cell structures can counteract impairments during biogas production. This comprehensive approach has not been performed before for AD systems and will be carried out with the help of several national and international cooperation partners.