TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Component: The phase separator is a three-phase separator and is further capable of separating a gas and liquid from a solid. The upflow reactor has a liquid clarification zone above the separation units. It includes an anaerobic fermentation reaction zone for wastewater liquid in which gas is generated within the reaction zone. It also has a gas collection chimney extending longitudinally within the reactor. The upflow reactor may include additional separation unit(s). It further includes pressure controller for the collected gas at a top of the gas collection chimney.Preferred Arrangement: The separation units are arranged such that they define a gas collection area. The units are arranged in transversely extending row(s). The anaerobic fermentation reaction zone lies between the first and second rows. The separation units within each row are arranged such that the gas collection area is formed between adjacent separation units. The phase separators are on top of the reaction zone. Only liquid communication occurs between the reaction zone and clarification zone through the coagulation areas. The gas collection chimney is in liquid communication with the reaction zone. The separation units comprise 60-90% of the cross-sectional area of the upflow reactor. Preferred Dimension: The cross-sectional area of the gas collection chimney is 10-40% of the cross-sectional area of the upflow reactor apparatus.    TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Component: The wastewater liquid comprises a biomass solid for returning to the reaction zone.Preferred Process: The solids are separated from the liquid and gas by directing the solid downwards along the deflectors to the reaction zone. The fluid upflow velocity in the clarification zone is at most 70 (preferably 2-20) m/hour while that in the reaction zone is at most 50 (preferably 2-20) m/hour. The gas upflow velocity in the anaerobic fermentation reaction zone is not greater than 40 m/hour. The inlet velocity to the two separation units is at most 10 (preferably 4-6) times a fluid upflow velocity in the reaction zone. Separation of liquid and gas within an upflow reactor zone also includes passing the liquid through the anaerobic fermentation reaction zone, directing liquid from the coagulation area into a second separator, and removing the liquid from the upflow reactor.