Chemical looping combustion (CLC) is a low-cost CO2 capture technology with a low energy penalty. Bio-energy with CO2 capture and storage (BECCS) opens up the possibility for negative CO2 emissions involving the removal of CO2 already emitted into the atmosphere. The oxygen needed for combustion in CLC processes is supplied by a solid oxygen carrier circulating between the fuel reactor and the air reactor. In this work, the combustion of different types of biomass, such as pine sawdust, olive stones and almond shells, was studied in a continuous 1.5 kW(th) CLC unit. A mixed Cu-Mn oxide was used as the oxygen carrier. This material releases gaseous oxygen when reduced, resulting in Chemical looping combustion with oxygen uncoupling (CLOU). The released oxygen reacts with both the volatiles and char generated inside the fuel reactor when biomass is fed into it. The oxygen carrier is reoxidized in air inside the air reactor. High CO2 capture and 100% combustion efficiencies were achieved with this Cu-Mn oxygen carrier. The oxygen concentration inside the air reactor did not affect CO2 capture efficiency under the studied conditions.