This preliminary investigation demonstrated that diverse sludge granules could be cultivated directly in a single continuous-flow membrane bioreactor (MBR) with the same carbon source and nutrients in influent. Results indicated the obtained sludge granules not only had obviously different colors in their appearance, but also exhibited quite diversified microbial compositions. This interesting phenomenon revealed richer microbial diversity occurring in the MBR, which was very beneficial to the stability of the microbial ecosystem within the MBR, and the efficacy of removing organic pollutants and converting nutrients. It was speculated that the main reason leading to the formation of diverse sludge granules was the micro multi-habitat produced by the complex internal circulation within the MBR. Future's work should be focused on the mechanism, stability and kinetic of forming the diverse sludge granules in MBRs, and further verify the prospective of this novel finding in practical application fields. (C) 2017 Elsevier B.V. All rights reserved.