About

The use of bio-residues from agriculture for value addition is often limited, otherwise operators fear process instabilities. This hinders the closing of regional material cycles.

Dark fermentation optimised for short-chain carboxylic acid production has a great potential to adapt any undefined feedstock mixtures into small building blocks, which can be used to products of higher value. This process can be performed in plug-flow bioreactors. In order to achieve a higher efficiency and robustness, enzymes and microbes shall be added as identified in automated screening; the application of gradient measurements along the plug-flow reactor and polarizability measurements to assess the activity of microorganisms in several parts of the plug-flow bioreactor and in different scales shall contribute to new options for process control. The short-chain carboxylic acids from dark shall be used for the production of the polyunsaturated fatty acid docosahexaenoic acid (DHA) in a subsequent cultivation.

The objectives of PASS-BIO are: 

• Screening system for optimised enzyme addition depending on the feedstock.
• Cheap and easy-to-operate plug-flow type digester for a decentralised operation.
• Monitoring of gradients for real-time process optimisation and flexible operation.
• Development of an expert system to achieve lower risks of severe process failures.
• Thin slurry (recirculate) separation and suitable tretament for the separation of short-chain carboxylic acids for DHA production.

Results

So far achieved while the project is ongoing:

• A workflow to rapidly identify microorganisms and enzymes to support feedstock degradation was developed on an automatic liquid handling roboter station.  
• The most suitable enzymatic cocktail was determined in feedstock degradation experiments with lignocellulose and other bio-residues and is applied in dark fermentation experiments now.
• A methodology has been set that allows to estimate the acid formation potential in parallel experiments in the shake flask scale.
• An experimental set up for lab scale experiments was designed, constructed and sucessfully implemented at two project partners.
• The gradient-based measurement monitoring in the dark fermentation plug-flow reactor was installed, first results are promising for process control.