Valorisation of dairy side streams using processing technology and biotechnology

Dairy side streams, namely, whey permeate (WP) and delactosed permeate (DLP), are a key challenge for dairy processing. Excess WP and DLP volumes can be a sustainable bottleneck for the expansion of dairy industries and finding a sustainable disposal route with environmental and economic incentive for these dairy side streams can be challenging. This thesis explores a second-generation (2G) biotechnological process for the bioconversion of dairy side streams into bio-based L-lactic acid. WP and DLP are supersaturated in fermentable lactose that can be converted biochemically into biodegradable bio-based monomers such as lactic acid (LA). The bioconversion of whey side streams into LA and subsequent polymerization into biodegradable polymers such as polylactic acid creates new value chains in the dairy industry but also the opportunity to reduce the environmental and economic burden associated with WP and DLP processing. However, WP and to a greater extent, DLP, have a high mineral content which can affect microbial fermentation performance and increase the cost and complexity of the downstream purification process, thus, requires a pre-treatment demineralisation step. At pilot-scale, the pre-treatment of dairy side streams into a suitable fermentation substrate was investigated using two different pre-treatment methods, NaOH and Ca(OH)2 pre-treatment, applying different dairy side stream feedstock types. Furthermore, microbial L-LA fermentation performance was then investigated at pilot-scale (100 L and 3000 L) using both NaOH and Ca(OH)2 pre-treated dairy side streams as the fermentation substrate. Analytical data was compiled and assessed after completing all stages of the 2G LA biotechnological process, namely, pre-treatment demineralisation, microbial L-LA fermentation, and the downstream purification of the lactate salt into high-quality L-LA. The generated data was then used to develop a techno-economic assessment to validate if the valorisation of dairy side streams into LA was economically feasible at industrial scale production. To sum up, this thesis underpins a feasible bioprocessing valorisation route for WP and DLP to produce L-LA. A 2G LA valorisation platform solves the issue of finding a sustainable solution for excess dairy side stream volumes, creates a new value chain, and supports the transition of dairy industries into a circular dairy bioeconomy.