Embodiments of the invention describe an apparatus, method, and system of wastewater treatment using modular membrane bioreactor (MBR) cartridges. In one embodiment, said method of wastewater treatment includes adjusting the number of activated modular MBR cartridges in a container and adjusting the wastewater processing rate of the container to dynamically change the throughput of a fixed-size wastewater processing container. According to one embodiment, said method can include utilizing modular MBR cartridges to provide for a fault-tolerant wastewater treatment container.