The overall productivity of any bioprocess is determined by the stability and the efficiency of the biocatalyst, the amount of product produced in a given reaction volume and the yield of product recovery. We use cyanobacteria for splitting water into hydrogen and oxygen driven by energy of the light reaction of photosynthesis. The turnover number of the biocatalyst (kcat in s-1) and its stability over time are determining the amount of hydrogen produced in a given reaction volume (mass of H2 formed per mass of biocatalyst, the total turnover number). This again is limited by the quantum efficiency of the reaction network and thermodynamic and metabolic constraints. Ideally, product recovery is integrated in a continuous production process. We integrate metabolic engineering of natural photosynthesis with continuously operated microreactors based on catalytic biofilms as biocatalysts with membrane technology for maximizing surface to volume ratios and mass transfer rates.