The MEC is based on modifying a microbial fuel cell (MFC) in two ways: adding a small amount of voltage (>0.2 V) to that produced by bacteria at the anode; and not using any oxygen at the cathode. The addition of the voltage makes it possible to produce pure hydrogen gas at the cathode. This MEC/BEAMR system is therefore operated as a completely anaerobic reactor. The voltage needed to be added can be produced using power from an MFC or by using hydrogen gas produced by the MEC in a conventional hydrogen fuel cell. The idea behind this system is that the protons and electrons produced by the bacteria can be recombined at the cathode as hydrogen gas-- a process called the hydrogen evolution reaction (HER). Theoretically we need 0.41 V to make H2 from acetate, and the bacteria produce ~0.2 to 0.3 V. Thus, we only need to add about 0.2 V or more to make hydrogen gas in the MEC/BEAMR. This voltage is much less than that needed for water electrolysis, which is about 1.8 V in practice. It takes a lot of energy to split water, but "splitting" up organic matter by the bacteria is a thermodynamically favorable reaction when oxygen is used at the cathode. In the MEC process, no oxygen is present and the reaction is not spontaneous for hydrogen production unless a small boost of voltage is added to that produced by the bacteria. Thus, the MEC process is more of an "organic matter electrolysis" procedure