Abstract: In metal machining processes, the regulation of heat generation and lubrication at the contact point are achieved by application of a fluid referred to as metalworking fluid (MWF). This has the combined features of the cooling properties of water and lubricity of oil. MWFs inevitably become operationally exhausted with age and intensive use, which leads to compromised properties, thereby necessitating their safe disposal. Disposal of this waste through a biological route is an increasingly attractive option, since it is effective with relatively low energy demands when compared to current physical and chemical options. However, biological treatment is challenging since MWF are chemically complex, including the addition of toxic biocides which are added specifically to retard microbial deterioration whilst the fluids are operational. This makes bacterial treatment exceptionally challenging and has stimulated the search and need to assess technologies which complement biological treatment. In this study the remediation, specifically of the recalcitrant component of a semi-synthetic MWF, employing a novel hybrid treatment approach consisting of both bacteriological and chemical treatment, was investigated. Three chemical pre-treatment methods (Fenton’s oxidation, nano-zerovalent iron (nZVI) oxidation and ozonation) of the recalcitrant components followed by bacterial degradation were examined. The synergistic interaction of Fenton’s-biological oxidation and nZVI-biodegradation led to an overall COD reduction of 92% and 95.5% respectively, whereas pre-treatment with ozone reduced the total pollution load by 70% after a post-biological step. An enhancement in biodegradability was observed after each of the chemical treatments, thus facilitating the overall treatment process. The findings from this study established that the use of non-pathogenic microorganisms to remediate organic materials present in MWF wastewater is a favourable alternative to energy demanding physical and chemical treatment options. However, optimal performance of this biological process may require chemical enhancement, particularly for those components that are resistant to biological transformation.