Microalgae and ammonia: A review on inter-relationship

Abstract With increasing threat of global warming to the livelihood of planet earth, reduction of carbon emission to the atmosphere is inevitable. Carbon emission reduction can be achieved through carbon capture and replacement technologies. Microalgae and ammonia (NH3) have been known to be carbon capture and carbon replacement option, respectively. This paper examines the inter-relationship between these two candidates with carbon reduction potential: microalgae and ammonia, and their future perspectives. Firstly, impact of ammonia presence in natural habitat of microalgae is identified, from the aspect of microalgal growth characteristic, photosynthetic performance, and biochemical composition. Possible solutions of ammonia removal in aquatic system include biotreatment with microalgae, nitrification–denitrification with bacteria, ion exchange using zeolites, and membrane contactor technologies. Next, with ammonia being identified as potential future energy source, conventional ammonia production, as well as bio-ammonia production are discussed. Microalgae technology used to produce syngas through pyrolysis and hydrothermal gasification (HTG) are reviewed and is identified to produce ammonia to achieve carbon emission reduction target. Finally, the challenges and impacts of bio-ammonia production using microalgae are highlighted. The main factors determining the sustainability of microalgae-based technology are energy demand, environmental impacts, and production cost, with each having challenges to varied extent. Governmental policies that drive the development in this field are also discussed. However, further research on the impact on environment and energy consumption need to be thoroughly carried out, to enable clear improvement over current usage of fossil fuel.