In this paper a feedback linearization control (FLC) strategy was developed and tested for controlling chemical oxygen demand (COD) degradation in an upflow anaerobic sludge blanket (UASB) reactor used for leachate treatment. The strategy developed allows regulation of the COD concentration at the output stream of the reactor without varying the flow rate, instead we use the temperature as the input control signal. This alternative shows a good perspective for controlling industrial scale reactors with high organic loads and limitations for volume expansion. The control approach is based on a simple model to describe the process and an asymptotic observer to estimate the state variables.