Biological nitrogen removal from sewage and various industrial wastewaters via nitrification and denitrification is widely reported. However, achieving nitrification in recalcitrant refinery wastewater is challenging due to inhibition and washout of nitrifiers. This study addressed the challenge of achieving nitrification and carbon removal in synthetic refinery wastewater (SWW) by acclimatisation (and granule cultivation) of the activated sludge from dairy industry in a sequencing batch reactor (SBR) under aerobic conditions with influent chemical oxygen demand (COD) of 225.8 mg/L (containing various carbon and nitrogen containing organic compounds present in refinery wastewater) and total nitrogen (TN) of 30 mg/L (ammonium-N, organic-N and nitrate-N). Two acclimatization strategies were tested: (i) direct exposure of sludge to 100% SWW, and (ii) gradual acclimatisation approach where a simple carbon source (sodium acetate) was replaced by SWW in a stepwise manner, maintaining constant COD (225.8 mg/L). Direct exposure to 100% SWW inhibited nitrification, achieving ~60% COD removal and negligible TN removal. Gradual acclimatization facilitated granule formation and improved SBR performance, achieving 95% COD removal and complete nitrification, with sludge volume index (SVI) < 100 mL/g. High solids retention time (SRT) of 65 days, hydraulic retention time (HRT) of 40 hours, and sludge granulation possibly promoted nitrification and achieved excellent COD removal. Presence of nitrifiers was confirmed via fluorescent in-situ hybridization (FISH). However, denitrification was observed to be limited, which thus affected TN removal.