Development of on-site enzyme production to obtain sugar-rich hydrolysates from lignified biomass using straw as an example

The production of bio-based chemicals and polymers from renewable raw materials is an important topic for the future. This is why PFI has been intensively involved in the field of “white” biotechnology for years and has developed digestion processes and fermentation technologies in various research projects in order to utilise agricultural residues for the production of biobased products. However, the high cost of cellulose-splitting enzymes is still a major obstacle to the production and utilisation of these raw materials on an industrial scale. In order to significantly reduce these costs, the PFI is starting to establish on-site enzyme production as part of a joint project.

Agricultural residues as well as by-products and co-products have enormous potential as a source of raw materials for the sustainable production of biochemicals and bio-based plastics. In Germany alone, around 50 million tonnes of cereal straw are produced every year. Even if a large proportion of this cereal straw has to be returned to the cultivated areas to form new humus, a usable proportion of at least 15 million tonnes can be identified for the production of bio-based chemicals and polymers.

In order to be able to use cereal straw for the extraction of raw materials, adequate digestion technologies must be developed to utilise the sugars it contains by fermentation. One promising pre-treatment method is hydrothermal digestion using thermal pressure hydrolysis (TDH) with subsequent enzymatic hydrolysis. TDH has been established and optimised in various projects at PFI, so that almost complete hydrolysis of the hemicellulose fraction to monosaccharides is possible.

However, the enzymatic hydrolysis of the cellulose fraction is still a critical point. Although TDH pre-treatment significantly improves enzymatic hydrolysis, the level of enzyme costs is still too high for economic use: at least €400 is currently incurred for extensive enzymatic hydrolysis of 1 tonne of straw (after thermal pre-treatment). These costs are the reason why biopolymers and biobased chemicals are not yet available on the market for most applications.

In order to reduce the costs of enzyme production, on-site enzyme production is to be developed as part of the research project. Part of the straw after TDH will be used for the production of the required cellulolytic enzymes, which will then break down the remaining TDH straw. This provides a glucose-enriched fermentable hydrolysate that is suitable for the biotechnological production of various target products.

The application for this project was submitted to the Agency for Renewable Resources (FNR) and has already been assessed as eligible for funding.

 

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