NOVELTY - A bioreactor (BR) comprises 1st processing unit (ZF), 2nd processing unit (Z2), last processing unit (ZL), and optionally, additional processing units, e.g. 3rd processing unit (Z3), between 2nd processing unit (Z2) and last processing unit in a plug flow configuration; greater than or equal to 1 forward circulation systems for circulating biomass (BM) from 1st processing unit to last processing unit and/or additional processing units; and greater than or equal to 1 reverse circulation systems for circulating biomass from last processing unit and/or additional processing units to 1st processing unit.    USE - A bioreactor for biologically treating water fluids, such as fresh waters, process waters, waste waters, slurries, solids, biomass and/or gas, for biologically producing desired end product by biomass and/or biomass and biogas, for nitrogen, phosphorus, and/or solids removal, for use in aerobic, anoxic, and/or anaerobic process/processes, and for producing targeted end products, including but not limited to production of methane, ethanol or microbial biomass, as a bioreactor for performing microbially a chemical reaction between greater than or equal to 2 chemical compounds provided to the system, or as a bioreactor treating biomass present in water fluids (all claimed).    ADVANTAGE - The bioreactor has increased processing speed and efficiency, simplified system design, and reduced pumping needs, adjusts itself to having excess processing capacity reserve at its normal operating point, which allows higher peak loadings than conventional system, and allows processing to be performed more uniformly along processing units, enabling more uniform aeration in aerated systems, more uniform processing profile for optimum total system volume, and reducing phasing.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for manufacture of bioreactor for biologically treating water fluids (WF), producing desired end product by biomass and/or producing biomass which involves arranging 1st processing unit, 2nd processing unit, last processing unit, and optionally, additional processing units between 2nd processing unit and last processing unit in a plug flow configuration, greater than or equal to 1 forward circulation systems, and greater than or equal to 1 reverse circulation systems.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a basic biomass circulation system with one loop.    Biomass (BM)    Bioreactor (BR)    Water fluid (WF)    2nd processing unit (Z2)    3rd processing unit (Z3)    1st processing unit (ZF)    Last processing unit (ZL)