Production of microalgae biomass in a two-stage continuous bioreactor. Control of microalgae-bacteria competition by spatial uncoupling of nitrogen and organic carbon feeding

The spatial uncoupling of nitrogen and organic carbon is proposed to control the competition between microalgae and bacteria in continuous bioreactors. A series of two continuous stirred bioreactors with recycle is considered where the upstream and the downstream reactor are fed with only the nitrogen and only the organic carbon source, respectively. A Droop-like model and a multiplicative Monod model are used to describe microalgae and bacteria growth kinetics, respectively. The stability regions of steady state solutions corresponding to pure microalgae cultures, pure bacteria cultures, and microalgae-bacteria consortia are identified by bifurcation analysis of the mass balance equations governing reactor dynamics. By capitalizing the competitive advantage of microalgae to uncouple nitrogen and carbon uptake, the proposed configuration allows attaining global stability of the microalgae and the microalgae-bacteria solution. Analytical approximations are derived for stability boundaries of steady states, providing guidelines for the design and control.