**4. Conclusions**

Wastewater treatment by applying biofilm has been developed over the years, and various biofilm processes are playing important roles at different stages of wastewater treatment industries. MBBR concept based on biofilm is widely used for organic and inorganic removal in both industrial and municipal wastewater remediation. It is approved to be a compact, energy-efficient, and robust solution comparing to a traditional activated sludge process. Due to biofilm growth on a protected area, different organism species coexist in the MBBR biofilm clusters which enhances their resilience to the environmental condition variations. The development based on MBBR to even compact process such as CFIC and HyVAB and the integration of MBBR with other high-rate and efficient processes could potentially reduce the footprint and complexity of wastewater treatment. Future studies to improve MBBR system for high mineral content wastewater treatment, optimize carrier designs and understand the correlation between protected area and organism species in different environmental condition, the biofilm growth, and detachment mechanisms induced by external forces and improving the energy efficiency for enhanced mass transfer are interesting topics to be explored.
