The processes based in microalgae imply new challenges on modelling as well as control, due to the complex nonlinear dynamics and variants during the course of time. These can be cultivated in closed systems called photobioreactors, through which it is possible to control the conditions of the crop, with the purpose of increasing the production of biomass or metabolites. The optimization of the conditions of growth in relation to light is essential for the increase of biomass. In this paper, a proposal is presented to control the intensity of light applied to a batch PBR, using the strategy of active disturbance rejection control (ADRC) with the goal of increasing biomass. Under this paradigm: 1) a substantial simplification of the design of the laws of control is obtained, 2) the complexity of the system is reduced to a linear disrupted system, 3) the high uncertainty of the internal dynamics are worked liked equivalent disturbances at the entrance, 4) the internal and external disturbances that affect the behavior of the system are worked in a unified manner and 5) the estimation of the unified disturbances are done in line by a linear observer of extended state in schemes of control based on the observer. The proposal of control is illustrated and evaluated on a simulation level. In the analysis, the performance of the strategy was contemplated against the variation of parameters. The simulations show the excellent performance against the different sensibility analysis considered, highlighting the strength of the strategy.