NOVELTY - Reactor assembly (10) comprises a reactor including an attached shaft comprising a vertical slow-flow zone (50) having first and second ends, first vertical fast-flow zone (70) adjacent to the slow-flow zone, where each fast flow zone has first and second ends, the first ends are in direct fluid communication, and the second ends are in indirect fluid communication through reactor head (40), and a first gas-liquid injection assembly (60) adjacent to and in fluid communication with the fast-flow zone. The slow-flow zone, fast-flow zone, and reactor head define a circulation loop.    USE - The reactor assembly is used to produce hydrogen or methane. It is used in acetone-butanol-ethanol fermentation process to produce product selected from acetone, butanol, and/or ethanol, and in energy production process to produce biofuel comprising biodiesel, bioethanol, or biobutanol. It is useful for a reactor system (claimed) i.e. vertical shaft reactor system for carrying out a chemical or biological reaction. The reactor system is used for producing renewable energy. It is a deep shaft fermentation system. The reactor assembly is used to carry out anaerobic microbial water shift reaction of carbon monoxide gas to generate molecular hydrogen; and oxidative biological treatment of wastewater.    ADVANTAGE - Using the reactor system, the amount of reactant in the feed gas (e.g. the amount of carbon monoxide (CO) consumed in CO fermentation processes or the amount of total dissolved oxygen in wastewater treatment processes) may be optimized during continuous operation of fermentation. The deep shaft reactor system may be operated to maximize biochemical reaction, e.g. to ensure 100% utilization of gaseous reactant. Deep shaft reactor system is thus designed such that the pressure of operation, the concentration of biomass within each of reactors, and/or the reactant content of the feed gas to each of reactors of reactor assemblies may be modified (i.e. the depth varied) to provide optimum conditions for bacterial fermentation. The design of deep shaft reactor system with deep shaft reactors in series with various inlet concentrations of reactant gas in the fermentation feed gas and/or various depths allows manipulation of the optimum operating conditions (toxicity points) of the bacteria. Such serial design provides flexibility of operation. Being able to adjust the microorganism concentration and feed gas to each of the series of reactor assemblies within the deep shaft series enables optimum conversion of reactant to desired product. The use of multi-nozzle injection assembly makes it possible to optimize the concentrations and/or the temperature of nutrients or reactants provided to different regions of the bioreactor according to the concentrations of the microorganisms, thus minimizing potential toxicity and maximizing production efficiency. The two-nozzle assemblies promote enhanced gas to liquid transfer rates, and permits effective gas injection control. The reactor assembly is durable and explosion-proof and has the ability to run continuously.    DETAILED DESCRIPTION - A reactor assembly (10) comprises a reactor including a head (40) including a fluid inlet and an effluent outlet, and an attached shaft comprising a vertical slow-flow zone (50) having first and second ends, first vertical fast-flow zone (70) adjacent to the slow-flow zone, where each fast flow zone has first and second ends, the first ends are in direct fluid communication, and the second ends are in indirect fluid communication through the head, and a first gas-liquid injection assembly (60) adjacent to and in fluid communication with the fast-flow zone; and a chamber comprising a radiation source, where slow-flow zone, fast-flow zone, and head define a circulation loop. INDEPENDENT CLAIMS are included for:    (1) a process utilizing a reactor assembly to produce hydrogen or methane comprising introducing into the reactor, at least one species of microorganism, a liquid nutrient medium, and carbon monoxide or biodegradable biomass to form a mixed liquor solids suspension (MLSS), where microorganism is capable of converting carbon monoxide to hydrogen via water gas shift reaction or capable of fermenting biomass to form methane; photoactivating the microorganism; circulating the MLSS in the circulation loop under anaerobic conditions; injecting an inert gas into the fast-flow zone to create a gas lift pump; and recovering hydrogen or methane from the reactor;    (2) acetone-butanol-ethanol fermentation process utilizing a reactor assembly to produce a product selected from acetone, butanol, and/or ethanol, comprising introducing into the reactor, a strain(s) of bacteria, a liquid nutrient medium, and a carbon-rich substrate, to form MLSS, where introduced bacteria are capable of fermenting the carbon-rich substrate to produce the product; optionally photoactivating the microorganism; circulating the MLSS in the circulation loop under anaerobic conditions; injecting an inert gas into the fast-flow zone to create a gas lift pump; and recovering the product from the reactor; and    (3) energy production process utilizing reactor assembly to produce biofuel, comprising introducing into the reactor, at least one species of microorganism and a liquid nutrient medium to form MLSS; irradiating MLSS with light; circulating the MLSS in the circulation loop; injecting carbon dioxide into the fast-flow zone to create a gas lift pump; and recovering from the reactor, biofuel.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of a vertical shaft reactor assembly.    Reactor assembly (10)    Reactor head (40)    Slow-flow zone (50)    Gas-liquid injection assembly (60)    Fast-flow zone (70)