Sugarcane bagasse (SCB) is one of the main residues of the sugar agroindustry; its complex lignocellulosic structure limits its biodegradation and utilization in the production of bio-based chemicals. This study evaluated the effect of hydrothermal pretreatment of raw SCB (HPSCB; 140 ℃, 15 min; 62.3% delignification) on lactic acid (LA) production. Enzymatic hydrolysis of HPSCB using Aspergillus niger enzymes achieved a maximum reducing sugar concentration of 11.98 g/L under optimal conditions (50 ℃, 80 PFU/g-SCBDW, 24 h). Subsequently, LA production was investigated via pre-hydrolysis followed by simultaneous saccharification and fermentation (SSF) using two microbial sources: the pure strain Pediococcus pentosaceus LB-25 and thermally treated anaerobic sludge (TTAS). Key variables included microorganism-to-culture medium ratio (10:90, 20:80, 30:70%), microbial source (pure P. pentosaceus vs. mixed TTAS consortium), and substrate (RSCB vs. HPSCB). In this pre-hydrolysis and SSF process, reducing sugar concentrations exceeding 40 g/L at 20 h using HPSCB or RSCB with P. pentosaceus at a 30:70 ratio. Significantly higher LA production with P. pentosaceus compared to TTAS: concentrations (11.51 g/L vs. 8.73 g/L), productivities (0.96 g/L·h vs. 0.18 g/L·h), and yields (0.57 g/g-SCBDW vs. 0.43 g/g-SCBDW) were achieved. This strategy demonstrates circular economy potential by valorizing SCB and anaerobic sludge (as carbon source and inoculum, respectively), reducing dependency on pure cultures/commercial enzymes while minimizing waste disposal. The approach provides a sustainable route for LA bioproduction and contributes to closing resource loops in the bioeconomy.