This data in brief (DIB) article is related to a Research article entitled 'Optimising an outdoor membrane photobioreactor for tertiary sewage treatment' [1]. Data related to the effect of substrate turbidity, the ammonium concentration at which the culture reaches nitrogen-deplete conditions and the microalgae growth rate under outdoor conditions is provided. Microalgae growth rates under different substrate turbidity were obtained to assess the reduction of the culture's light availability. Lab-scale experiments showed growth rates reductions of 22-44%. Respirometric tests were carried to know the limiting ammonium concentration in this microalgae-based wastewater treatment system. Growth rates (μ) of green microalgae Scenedesmus and Chlorella obtained under outdoor conditions; i.e. 0.40 d−1 (R2 = 0.993) and 0.43 d−1 (R2 = 0.995), respectively, can be useful to obtain optimum operating conditions of membrane photobioreactor (MPBR).