Plug flow reactor–based Acid fermentation for Small-Scale BIOrefineries


The multidisciplinary PASS-BIO project aims to establish a suitable, cost-efficient bioreactor module for the flexible conversion of a wide variety of feedstock to produce either short-chain carboxylic acids in an acidic fermentation or methane as alternative.

The module shall follow a plug-flow principle. Although this technology is not new, its full potential concerning process robustness in comparison to the common stirred tank digester concepts is not used. Intensified monitoring, which takes advantage of the formation of spatial gradients along the flow direction, is used to make the operation autonomous and to provide an expert system for  unexperienced users. 

The importance and impact of gradient formation, also in relation to feedstock flexibility, was not investigated in plug flow reactors so far, although gradient formation is a key characteristic of plug-flow type reactors. We postulate that the consideration of gradient formation will increase process stability at various feedstock compositions beyond the current state-of-the-art of anaerobic digesters.

Several probe installations in the liquid phase along the length of the reactor will ensure a proper monitoring of these gradients, which provide indirect information of the hydrolysis (degradability) and acid formation.

Besides monitoring, additives for the hydrolytic conversion are of increasing importance to ensure robustness for feedstock variation, however, tailored solutions for each process are required.

This demand has not been coupled to the advantages of increased automation and parallelization on a plate scale so far. In order to ensure a fast adaptation of the plug-flow process to various feedstock resources, and to achieve solutions to control the process in case of insufficient hydrolysis, a small scale screening system methodology will be developed that allow the rapid identification of suitable additives.

These will be tested in a scaled-down plug-flow reactor module, so that a whole strategy for the implementation and conduction of a plug-flow based acid fermentation with various feedstock is achieved. In order to couple this approach to other bioprocesses for value addition, a thin slurry separated from the dry matter of the acid fermentation, which contains carboxylic acids, will be applied as feedstock for a  heterotrophic, microalgae-based production of the polyunsaturated fatty acid DHA.

In a final step, a demonstration of the plug-flow based digestion will be conducted at two associated partners, one industrial company and an eco-village. The feasibility of decentralized operation of such a concept, will be evaluated and discussed with experts and lay people in public presentations.

Finally, economic and ecologic assessments of the applied techniques and concepts will provide data for future integration into regional cycles. In summary, the whole upstream process shall be made easier and reliable for fast adaptation as a contribution towards smart bioproduction grids.  


Dr. Stefan Junne

Technische Universität Berlin (TUB), Germany


Project partners:

Technische Universität Berlin (TUB), Germany  

Natural Resources Institute Finland (Luke), Finland

Ecole Centrale de Lille (ECL), France