The influence of the carbon oxidation-reduction state (CORS) of organic pollutants on their biodegradation in enclosed algal-bacterial photobioreactors was evaluated using a consortium of enriched wild-type methanotrophic bacteria and microalgae. Methane, methanol and glucose (with CORS -4, -2 and 0, respectively) were chosen as model organic pollutants. In the absence of external oxygen supply, microalgal photosynthesis was not capable of supporting a significant methane and methanol biodegradation due to their high oxygen demands per carbon unit, while glucose was fully oxidized by photosynthetic oxygenation. When bicarbonate was added, removal efficiencies of 37 +/- 4% (20 days), 65 +/- 4% (11 days) and 100% (2 days) were recorded for CH4, CH3OH and C6H12O6, respectively due to the additional oxygen generated from photosynthetic bicarbonate assimilation. The use of NO3 instead of NH4+ as nitrogen source (N oxidation-reduction state of +5 vs. -3) resulted in an increase in CH4 degradation from 0 to 33 +/- 3% in the absence of bicarbonate and from 37 +/- 4% to 100% in the presence of bicarbonate, likely due to a decrease in the stoichiometric oxygen requirements and the higher photosynthetic oxygen production. Hypothetically, the CORS of the substrates might affect the CORS of the microalgal biomass composition (higher lipid content). However, the total lipid content of the algal-bacterial biomass was 19 +/- 7% in the absence and 16 +/- 2% in the presence of bicarbonate.