Palm oil mill effluent (POME) – a wastewater from the palm oil milling process is beneficial as a low cost carbon source for microalgae growth. This does not only help clean the wastewater but also reduce the algal cultivation cost. In this study, the growth rate, biomass productivity and biochemical compositions of Chlorella sp. grown in diluted POME under outdoor conditions using a 200-ml capacity high rate alga pond (HRAP) and two closed photobioreactors (PBR) i.e. annular and flat panel were assessed. The strain, Chlorella sp. grown on 5% of POME in a flat panel PBR exhibited the highest specific growth rate of 0.5 per day and biomass productivity (137.5 mg litre^-1 per day) followed by those in HRAP and annular PBR. Additionally, a good growth of Chlorella sp. in POME could sufficiently utilise the nutrients of POME such as phosphate (PO₄), nitrate (NO₃), nitrite (NO₂) and organic substances. The extracted algal oil from the diluted POME culture (5%) showed decrease in the saturated fatty acids and an increase in the polyunsaturated fatty acids compared to those cultured in the standard Bold’s Basal Medium (BBM). The biochemical compositions of the algae grown in the flat panel PBR were the highest with lipid, protein and carbohydrate productivity of 17.9 mg litre^-1 per day, 34.7 mg litre^-1 per day and 21.4 mg litre^-1 per day, respectively. The microalgae cultivation in diluted POME had not only shown good potential as a biodiesel feedstock based on the fatty acids profile but also the ability to reduce some pollutants e.g. PO₄, NO₃, NO₂ and chemical oxygen demand (COD) in the biological wastewater treatment.