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

The multidisciplinary PASS-BIO project aimed to establish a bioreactor module for the flexible conversion of a wide variety of feedstock following a plug flow principle. Although this technology is not new, it's full potential in terms of process robustness in comparison to the common stirred tank reactor concept is not used. Several probe installations in the liquid phase along the length of the reactor ensured a proper monitoring and the development of an expert system. Feedstock pre-treatment methods were applied and tailored to the requirements of this reactor type. The application of residues as fertilizer and the use of products as nutrients in other bioprocesses like polyunsaturated fatty acid production for fish feed was investigated to perform a proof-of-concept study for a new, low-cost and easy-to-operate module for a sustainable small-scale biorefinery. Finally, economic and ecologic evaluation shall be conducted. The partner specific work covered: Partner 1: Design and application of a lab-scale plug-flow bioreactor with several sensor and samples ports, investigation of the suitability of gradient-based monitoring in continuously operated dark fermentation at flexible feedstock load, including residual side streams, and scale up for a field demonstration of the concept. Partner 2: Potential of acid production from grass silage was studied by batch experiments in laboratory scale. After that, laboratory scale plug-flow reactor was examined by using manure and grass silage as substrates. First, manure was used to start up the process. Organic loading rate (ORL) of 2 gVS/Ld was used with 20 day hydraulic retention time (HRT). The aim was to overload the process to optimise short-chain acid production. This was done by increasing ORL gradually with grass silage. Acid phase was reached with ORL 10 gVS/Ld (HRT 5). After that, pH started to decrease and ORL was decreased to 8 gVS/Ld to maintain the acid production. pH, redox potential, conductivity as well as gas production (amount and quality) were followed continuously. Acid production as well as nutrient balance in residue was analysed frequently. Acid production raised up to 9.4 g/L during the continuous plug-flow process, being close to results gained from the batch process. Partner 3: In order to ensure a fast adaptation of the plug-flow process to various feedstock resources, a small-scale screening system methodology was developed to allow the rapid identification of the most suitable microorganisms consortia along with its operating conditions. The main objective was to define the best catalysts to use for the treatment of different biomass sources including microorganisms consortia, in a first hydrolysis step, or even enzyme cocktails. For fermentation, bacterial strains, directly isolated from feedstocks, were to be screened in order to identify a suitable consortium for biomass degradation into short chain fatty acids. For enzyme catalysis, several enzyme cocktails were screened on different biomass sources. The majority of the screened cocktails were produced from fungal strains that were directly isolated from the feedstocks, which consisted of maize silage, grass silage, cypress, wood chips and other landscape residues. We aimed to develop an innovative quick automated screening process to set the best biocatalytic biomass conditions to work in the plug-flow reactor on a wide variety of feedstocks.


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

Material from EUBCE 2019

Poster from EUBCE 2019