NOVELTY - An upflow reactor has a phase separator including two separation units (14a,14b), each with walls and parallel plates (40a, 40b). The separation units divert gas to the second side of the second wall of each separation unit. As the gas is diverted, it will pass upwardly into gas collection areas (58) where it pools and collects in the gas collection pockets (62) forming gas-liquid interface.    USE - The apparatus is for separating and purifying liquids in water treatment, physico-chemical wastewater treatment, biological wastewater treatment, food processing, production of pharmaceuticals, and other biotechnological applications. In wastewater treatment, the upward flow reactor is used in anaerobic sludge blanket processes, expanded granular sludge bed process, fluidized bed processes, gas-lift reactor processes, loop reactor processes, and biological aerated filter process. It is also particularly for production of fuel and ethanol.    ADVANTAGE - The apparatus enhances solids retention and improves flow characteristics of upflow reactor. It allows variation and optimization of separation space within an upflow reactor apparatus, providing enhanced separation efficiency. It is highly efficient in clarification and has a maximized clarification zone.    DETAILED DESCRIPTION - An upflow reactor comprises a phase separator including two separation units. Each of the separation unit includes first and second walls, and spaced parallel plates, which are vertically and horizontally inclined. A second side of the first wall and the first side of the second wall defines a coagulation area. The first wall adjoins a deflector inclined to the horizontal and vertical. The second wall adjoins one of the parallel plates. The deflector extends below and across the lower edges of the parallel plates. The separation units separates gas from liquid by diverting the gas to the second side of the second wall of each separation unit and by creating a circulation of liquid around the parallel plate(s) such that liquid is directed into the coagulation area.    An INDEPENDENT CLAIM is also included for a method of separating liquid and gas within an upflow reactor zone involving providing an upflow of liquid and gas within the upflow reactor; providing a liquid circulation around the parallel plate(s); and diverting the diverted gas from the gas collecting area out of the upflow reactor apparatus through a gas outlet.    DESCRIPTION OF DRAWING(S) - The figure shows an enlarged cross-sectional schematic representation of an upflow reactor apparatus with multiple phase separators.    Separation units (14a, 14b)    Parallel plates (40a, 40b)    Gas collection areas (58)    Gas collection pockets (62)