This study aimed to develop a wastewater treatment method that employs an advanced oxidation process (AOP) physico-chemical pretreatment (ultraviolet–hydrogen peroxide (UV-H2O2)) followed by biological treatment using an Acinetobacter sp. biofilm to treat toxic concentrations of phenol. This study shows that when the initial phenol concentration was 700 ppm, the biological treatment alone could not remove any of the phenol due to its toxicity to microorganisms. In contrast, using the combined treatment (AOP: UV-H2O2 with 300 ppm H2O2) for 3 h as a pre-treatment, followed by biological treatment, complete removal of phenol within only 18 h was achieved, as well as a 75 % decrease in organic matter concentration in the water. Treatment with UV-H2O2 alone reduced the phenol concentration by 20 %, but there was no reduction in the amount of organic matter (measured as total organic carbon (TOC)), indicating that the phenol transformed to aromatic by-products but without mineralization (monitored using HPLC). Toxicity tests performed on Artemia brine shrimp were conducted for all treatments; they demonstrated a 93 % reduction in toxicity following the combined treatment, whereas the separate treatments alone did not reduce toxicity. This study shows that the combination of treatments has great potential for removing contaminants that are not readily biodegradable, by reducing their concentrations and their decomposition products, and preventing the accumulation of toxic by-products.