The utilization of a cheap side stream is the core for biotechnological production of platform chemicals, such as, succinic acid. This study explores lab and pilot scale fermentation of Actinobacillus succinogenes (B1) and Basfia succiniciproducens (B2) to produce succinic acid from sulphide fibre sludge, a side product from pulp and paper industry. Both strains demonstrated efficient SA production, with lag phase of 2–3 h, accompanied by by-product formation of formic acid (FA) and acetic acid (AA). B1 outperformed B2 in SA concentration (28.4 g∙L-1 vs 20.4 g∙L-1) and yield ( 0.76 g·g-1 and 0.51 g·g-1), leading to its selection for pilot scale fermentations. Pilot scale fermentations using SFS hydrolysate as carbon source achieved SA yields of 0.62–0.66 g/g with productivities of 0.65 – 0.78 g∙L-1 SA. SFS hydrolysate, rich in glucose provided a promising substrate, yielding 23 g∙L-1 SA. Two downstream processing (DSP) methds were evaluated for SA recovery. DSP 1, involving microfiltration, electrodialysis, and ion exchange, achieved 62 % recovery but incurred losses during filtration and electrodialysis. DSP2 utilized activated carbon for decolorization, followed by microfiltration and crystallization, yielding 60.3 % SA recovery. Both DSP approaches produced high purity SA suitable for polymer applications. These results underscore the potential of SFS hydrolysate for sustainable SA production and highlight the need for process optimization, including fed-batch or continuous systems, to enhance yields and reduce costs. These findings contribute to advancing biobased monomer production as a viable alternative to fossil-based methods.