ABSTRACT Leachate wastewater (LWW) is characterized by slow biodegradation and low biogas production due to resistant materials and limited biological activity. Therefore, applying pretreatments is essential to improving biodegradation potential, which consequently boosts energy recovery. This study investigated the effects of ozone treatment on the bioavailability of LWW for anaerobic digestion with sludge. The ozone pretreatment significantly improved the bioremediation capacity of LWW, as shown by a reduction in COD from 13 570 to 4870 mg/L. Two reactors were compared: R2, which received ozone pretreatment, and R1, which did not. Results indicated that both reactors initially experienced a pH decline due to acidification and then stabilized around 7.3 by Day 25, signaling optimal conditions for bacterial activity. Total volatile fatty acid (TVFA) levels peaked earlier in R2 (2100 mg/L) compared to those in R1 (1500 mg/L), reflecting higher acid production in R2 during the hydrolysis phase. Afterwards, TVFA levels declined as methanogenesis progressed, with R2 showing a faster decrease, indicating more efficient biogas production. By Day 25, both reactors reached stable TVFA levels, marking the end of the methanogenic phase. R2 consistently outperformed R1 in both acid production and conversion efficiency.