In a
wastewater treatment system and process utilizing membrane bioreactors (MBRs), multiple, parallel series of tanks or stages each include, an MBR stage. Under conditions of normal flow volume into the
system, influent passes through several parallel series of stages or process lines, which might be, for example, an anoxic stage, an
aeration stage and an MBR stage. From the MBR stages a portion of M.L.S.S. is cycled through one or more thickening MBRs of similar process lines, for further thickening and further
processing and digesting of the
sludge, while a majority portion of the M.L.S.S. is recycled back into the main process lines. During peak flow conditions, such as
storm conditions in a combined
storm water /
wastewater system, all of the series of stages with their thickening MBRs are operated in parallel to accept the peak flow, which is more than twice normal flow. M.L.S.S. is recycled from all MBR stages to the upstream end of each of all the
parallel process lines, mixing with influent
wastewater, and the last one or several process lines no longer act to digest the
sludge. Another
advantage is that with the thickened
sludge in the last process line of basins, which ordinally act to digest the sludge, there is always sufficient
biomass in the
system to
handle peak flow, the
biomass being available if needed for a sudden heavy flow or an event that might bring a toxic condition into the main basins.