In the present invention, integrated processes for producing a biofuel are disclosed. Specifically, processes integrating photobioreactors with anaerobic digestion are disclosed. Anaerobic digestion can convert biomass into a biofuel. However, anaerobic digestion also produces carbon dioxide (CO2). Because it is a greenhouse gas, the production of carbon dioxide is not desirable. Algae can be grown in a photobioreactor as long as light, carbon dioxide, and water are provided. In the present invention, the anaerobic digestion process is integrated with the photobioreactor process thereby providing a useful solution for the carbon dioxide that is generated and providing a source of carbon dioxide for the photobioreactor.