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A student operating the pilot plant HMI


Changing the perception of the way that waste is viewed is central to the concept of a circular economy. An economy where limited primary resources are completely removed from, or produced for, society. Finding the ways to increase the value of waste by using it as an alternate to primary resources is the driving factor behind this increasingly talked about topic.

Bioplastics created using sustainably sourced materials have been a growing field of interest. Most current research has focused on finding the optimum conditions and ideal waste streams for creating the monomer that is most used to create these bioplastics, lactic acid. Much of this research has focused on optimising bench-scale laboratory tests, that produce large quantities of lactic acid but are highly controlled and would be costly to scale.

This bioprocessing-based project had 2 broad aims:

  • To demonstrate value addition to a waste stream at a much larger, pilot-scale.

  • To develop a procedure that demonstrated biological engineering and product recovery using the membrane pilot plant.

To achieve these aims, 30L samples of both idealised cellulosic water and industrial paper processing wastewater samples were fermented. This involved the direct addition of the bacteria Lactobacillus rhamnosus to create lactic acid in a 5-day fermentation period. While lactic acid was produced, understandably it was at a slower rate and a lower concentration than seen in literature as the fermentation wasn’t optimised. Fermentation of the synthetic cellulosic water proved a viable demonstration of biological engineering creating a maximum of 48mg/L/h of lactic acid. While lactic acid productivity during fermentation of the wastewater didn’t reach these levels (20mg/L/h), the increase in lactic acid was sufficient to demonstrate value addition to the waste stream.

To increase the concentration of the lactic acid, the membrane pilot plant was used as a product recovery system. By filtering these fermented mixtures, first by ultrafiltration to remove bacteria and undigested debris, and then by reverse osmosis to concentrate the lactic acid, the relative concentration of lactic acid compared to other metabolites increased.

Excitingly, this project has shown the viability of the pilot plant as a bio-product recovery system. The scaling of this process enhances the viability of a circular economy; one that doesn’t rely on primary resources to support its growth but focuses on sustainable and convenient resources that would otherwise go to waste.

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