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Demonstrating more efficient enzyme production to increase biogas yields

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Improved enzyme production process gives more biogas

Efficient conversion of biomass to biogas requires the availability of enzymes that are proven to be effective and can be produced at an industrial scale. However, to date, the use of enzymes has failed to live up to expectations and their observed effects are limited.

Energy

The EU-funded DEMETER project responded to this challenge by increasing the yield of the Myceliophthora thermophila C1-based biogas enzyme known as C1-enzyme, while reducing costs. “We aimed to increase the yield of the enzyme production process at an industrial scale as well as the down-stream processing, reducing the cost of the end product and making the enzyme available for wide-spread application in biogas production throughout Europe,” reports project coordinator Sandra Hinz. During the initiative an improved fermentation process for enzyme production was developed at lab scale. Researchers analysed the old fermentation protocol and adjusted different parameters based on the outcome of a mathematical model which they developed based on an improved production strain to give a better quality enzyme. In addition, the enzyme production process was optimised to increase the enzyme concentration by at least 50 %. “The improved fermentation process was validated first in a small pilot scale reactor and then increased to 1 500L and 15 cubic metre capacity reactor,” explains Hinz.

Improved properties

The work of the consortium resulted in increasing the enzyme production by 50 %. According to Hinz: “This means that in one fermentation run 50 % more enzyme can be produced and therefore less production rounds are needed. Next to the increased production, the downstream processing of the enzyme has also been improved. An enzyme recovery of more than 95 % was reached.” Project partners tested the enzyme’s efficacy in nine large-scale trials. “We used different types of biogas plants in these trials, such as for dry and wet fermentation, and plants that run on different substrates. The data from the large-scale plant trials was evaluated and showed that in some cases there was a possible increased efficiency of substrate degradation, although this was generally low,” comments Hinz. Researchers also noted changes in the rheological properties in the form of reduced power consumption of the agitators, better flowability of the digestate and also fewer floating layers. Thus, the positive effects of the addition of the enzyme on the fermentation process were discovered in the plants, indicating that an improvement of the biogas process is possible with the application of cost-effective dosages. DEMETER tested enzyme efficacy on a small scale and on a large scale in field trials. “In general, it has been found that the enzyme seems to show a small increase in efficacy,” Hinz observes. “The majority of plant operators reported improved flow behaviour of digestate, together with a better overall digestate quality. This resulted in fewer problems caused by clogging or floating layers and a decrease of long fibrous structures in the digestate. Data from a newly developed pipe viscometer clearly showed that the enzyme reduced the viscosity of the digestate.”

Financial and environmental benefits

The techno-economic assessment of the results of the field trials indicated that the biogas production system is more profitable when using the C1-enzyme compared to the traditional system, which does not use any enzyme. “Moreover, a life cycle assessment that included all the steps of the production of biogas, from waste feed materials collection and enzymes production to biogas storage, revealed a positive environmental impact compared to the traditional biogas production process,” Hinz points out.

Keywords

DEMETER, enzyme, biogas, fermentation, biomass, C1-enzyme, life cycle assessment

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