The project has made clear that, by using MBRs in a continuous fermentation process, plant output can be significantly increased at lower overall costs, using fewer resources.

A recently concluded ISPT project has successfully proven that the use of membrane bioreactors (MBRs) can lead to improved processing and cheaper, more sustainable fermentation products.

In traditional biotechnology processes, fermentation results in a complex mixture of residual components from the feedstock, the main product, co-products and the biocatalyst. To purify the main product, this mixture is treated in the downstream process in various unit operations. Typically, this occurs batchwise, where the full contents of the fermenter are processed in one go. However, for high-volume, low-margin products, continuous processes are more advantageous, because smaller fermenters can then be used for the same production capacity. 

The ISPT project studied to what extent the integration of membrane technology in the process could further increase throughput and reduce fermenter size, while avoiding wash-out of the biocatalyst. “Based on the conclusions of a pre-project phase, we decided to evaluate the technical and economic feasibility of MBR technology for two cases: lactic acid and beer production,” explains Heleen De Wever, Project Manager Biotechnology at VITO, one of the partners in the project.

Increasing productivity in lactic acid fermentation

“A switch from batch to continuous operation allowed us to increase the lactic acid output per unit of volume and time with a factor of 5,” says Heleen. “When we incorporated a membrane filtration step to achieve higher cell densities, the output was even increased with a factor of 25. In the case of lactic acid fermentation, the additional challenge was to combine this intensified process with the use of second-generation feedstocks. Industry is highly interested in the use of such feedstocks for sustainability and cost reasons, but they may contain inhibitors that have a negative impact on the subsequent fermentation process. This is where the detoxification part of the project came in. We were able to show that it is technically feasible to remove inhibitors from second-generation feedstocks. And perhaps even more interestingly, we have been able to prove that we were able to ferment a lignocellulosic hydrolysate in a membrane bioreactor.”

Producing beer of consistent quality

Continuous production and operation at higher cell densities could also improve beer production efficiency to a great extent. “We have shown that it can result in fast production of finished bright beer, without the need of a time-consuming maturation step,” says Heleen. “In this case, good colloidal stability and optimal flavour development in the final product were the major challenges.”

Environmental benefits

Due to reduced downtimes and higher productivity, continuously operating fermenters will typically be more efficient than batchwise processes. They therefore have clear economic and environmental benefits. For MBR concepts, this also needed to be proven. 

A Life Cycle Analysis (LCA) carried out by DSM, one of the industrial partners in the project, demonstrated that the carbon footprint of 1 ton lactic acid produced in an MBR from lignocellulosic feedstock is 43% lower than the carbon footprint of 1 ton of conventionally produced lactic acid on the basis of cane sugar. This is mainly thanks to the raw material (second-generation feedstock) and lower energy consumption.

Promising results

The project has made clear that, by using MBRs in a continuous fermentation process, plant output can be significantly increased at lower overall costs, using fewer resources. “Though further process optimizations are still required, these are promising results for the industry,” concludes Heleen.

About the FO-10-07 project

The FO-10-07 project started on 1 August 2012 with a 6-month pre-project, which was followed by a full project that ran until 31 May 2016. The project was coordinated by Corbion. The industrial partners were Corbion, DSM and Pentair, while VITO, TNO, ECN and the Catholic University of Leuven served as research partners.

About ISPT

The Institute for Sustainable Process Technology unites industry, universities, research organizations and SMEs in order to accelerate innovation and ultimately transform process technology into a green, clean, efficient endeavour. In addition to developing knowledge, the Institute fosters the demonstration and application of new technologies.

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