text: Two main ways of cultivating microalgae are raceway pond systems and photo-bioreactors. Raceway pond systems are constructed by a closed loop oval channel that has a paddle wheel to circulate water and prevent sedimentation. The channel is open to the air and its depth is in the range of . The pond needs to be kept shallow since self-shading and optical absorption can cause the limitation of light penetration through the solution of algae broth. PBRs's culture medium is constructed by closed transparent array of tubes. It has a central reservoir which circulated the microalgae broth. PBRs is an easier system to be controlled compare to the raceway pond system, yet it costs a larger overall production expenses.
  The carbon emissions from microalgae biomass produced in raceway ponds could be compared to the emissions from conventional biodiesel by having inputs of energy and nutrients as carbon-intensive. The corresponding emissions from microalgae biomass produced in PBRs could also be compared and might even exceed the emissions from conventional fossil diesel. The inefficiency is due to the amount of electricity used to pump the algae broth around the system. Using co-product to generate electricity is one strategy that might improve the overall carbon balance. Another thing that needs to be acknowledged is that environmental impacts can also come from water management, carbon dioxide handling, and nutrient supply, several aspects that could constrain system design and implementation options. But, in general, Raceway Pond systems demonstrate a more attractive energy balance than PBR systems.