A hybrid moving bed biofilm reactor–membrane bioreactor (hybrid MBBR–MBR) system has been tested in this study at two scales to analyse the scale-up effect. Two municipal wastewater treatment plants were used, one at laboratory scale (hybrid MBBR–MBRL) with a reactor working volume of 24 l and one at pilot scale (hybrid MBBR–MBRP) with a reactor working volume of 358 l. Hybrid MBBR–MBRL and hybrid MBBR–MBRP showed that the hybrid MBBR–MBR systems used in this research were reliable for organic matter removal with COD removal percentages of 90.97±2.55% and 95.56±2.01% for hybrid MBBR–MBRL and hybrid MBBR–MBRP, respectively. In hybrid MBBR–MBRL, the sludge retention time was higher but the biofilm density was lower due to the wall effect, so the two effects cancelled one another out and the COD removal efficiencies were found to be similar. The study identified the most influential variables and their effects on the process. Hybrid MBBR–MBRL and hybrid MBBR–MBRP were influenced by the attached and suspended biomass and temperature, while the influent loading rate only affected hybrid MBBR–MBRP. On the whole, hybrid MBBR–MBRP showed a better performance from the point of view of the kinetics of the heterotrophic biomass, with values of YH=0.6130mgVSSmgCOD−1, μm,H=0.0146h−1, KS=9.8852mgO2L−1, and bH=0.0031h−1. •Hybrid MBBR–MBR was reliable for COD removal (higher than 90.97±2.55%).•Hybrid MBBR presents a better kinetic behaviour and higher removal rate in pilot scale.•Variations of organic loading and temperature are two effects of the scale up.•The scale of working affects the sludge retention time and attached biomass.