Animal waste causes environmental problems like eutrophication of ground and surface water or the pollution of the atmosphere because of its high NH4+ content. The aim of our study was to fix the nitrogen of swine waste as biomass. Therefore, an isolated alga, Chlorella sp., and bacteria naturally living in liquid manure were grown in batch cultures (containing diluted swine waste supplied with a nutrient solution) and continuous cultures (undiluted liquid manure) to achieve reduction of NH4+ and total organic carbon (TOC) contents. For continuous cultivation, a photobioreactor of our own design was used. The batch cultivation of Chlorella sp. and bacteria in swine waste resulted in good growth of both groups of organisms and in a reduction of 25% NH4+ and 80% TOC. In the continuous cultivation a steady state was not achieved owing to a change in the composition of the bacterial population. NH4+ was totally removed, but NO2- (up to 100 mM) was transiently released. NO3- was not detected. These effects might be explained by the presence of heterotrophic nitrifiers, which are able to oxidize NH4+ to NO2- and to reduce NO2- to gaseous compounds.