Algal-bacterial consortia in biofloc systems

Due to the exponential growth of the human population, food production industries such as aquaculture require further expansion in order to cope with the problem of shortages in protein food supplies. However, in order to preserve the environment and natural resources, this expansion will need to take place in a sustainable way. The use of biofloc technology, which re-uses dissolved nutrients such as microbial biomass, holds a promising response to the global concern of making aquaculture more sustainable. Currently, operational parameters are mainly adjusted on a trial-and-error basis, and there is a clear need to shift towards a more scientific based approach in order to commercialize this technique. In this thesis, we mainly focused on co-cultivation of the microalgae Chaetoceros mülleri and a mixed nitrifier community consisting of Nitrosomonas sp. and Nitrobacter sp. and their usage as a non-intrusive technique for selective removal of pollution, such as ammonia (NH3-) and nitrate (NO3-) from wastewater with the added value of producing proteinaceous feed in situ that potentially serves as a food source for oyster spats. In general we can conclude that medium composition (e.g. nitrogen source) and addition of bacteria play an important role on algal growth, biomass production and nitrogen removal. The cocultivation of Chaetoceros mülleri and a mixed nitrifying community scored well in all different media, succesfully removing ammonium and nitrate. However only in medium containing a higher ammonium concentration compared to nitrate was algal growth not effected by the presence of the nitrifying community. As such further reseach is required to unravel the underlying mechanisms in these algal-bacteral co-cultivations. Keywords: Algal-bacterial consortia, Biofloc technology, Chaetoceros muelleri, nitrifier community.