The treatment of wastewater and sewage sludge is one of the major challenges in the water sector, mainly due to operational cost. Additionally, the overreliance on external chemicals as a carbon source for biological nitrogen and phosphorus removal (BNPR) heightens the operational cost and compromises environmental sustainability. Hence, this study focuses on internal recirculation of carbon from sewage sludge using dark fermentation to produce volatile fatty acids (VFAs). Sludge-derived VFAs have the potential to be used as a carbon source for BNPR, reducing the operational cost and carbon footprints of the water sector. Dark fermentation emerges as a cornerstone technology to enable VFA recovery or internal recycling; however, its integration within existing flowsheets remains underexplored, with a need to validate its techno-economic feasibility. Therefore, this study investigates the effects of DF operating conditions (e.g., pH and temperature) on VFA production from sewage sludge. The results indicate that pH and temperature significantly impact VFA yields and profile. The maximum VFAs concentration produced was 4914 mg/L at pH 9 and 10189 mg/L at pH 7.5 under 38°C and 55°C, respectively. The most predominant VFAs produced were acetic, propionic and valeric acids. This study advances our understanding of the impact of DF operational parameters on VFA yields and the potential of using DF as a biotechnology to recycle VFAs as a carbon source for BNPR in the water sector.