Growth and nitrogen removal capacity of Desmodesmus communis and of a natural microalgae consortium in a batch culture system in view of urban wastewater treatment (Part I).

The microalgal biomass applications strongly depend on cell composition and the production of low cost products such as biofuels appears to be economically convenient only in conjunction with wastewater treatment. As a preliminary study, in view of the development of a wastewater treatment pilot plant for nutrient removal and algal biomass production, a biological wastewater system was carried out on a laboratory scale growing a newly isolated freshwater algal strain, Desmodesmus communis, and a natural consortium of microalgae in effluents generated by a local wastewater reclamation facility. Batch cultures were operated by using D. communis under different growth conditions to better understand the effects of CO2, nutrient concentration and light intensity on the biomass productivity and biochemical composition. The results were compared with those obtained using a natural algal consortium. D. communis showed a great vitality in the wastewater effluents with a biomass productivity of 0.138 - 0.227 g L-1 d-1 in the primary effluent enriched with CO2, higher biomass productivity compared with the one achieved by the algal consortium (0.078 g L-1 d-1). D. communis cultures reached also a better nutrient removal efficiency compared with the algal consortium culture, with almost 100% for ammonia and phosphorous at any N/P ratio characterizing the wastewater nutrient composition. Biomass composition was richer in polysaccharides and total fatty acids as the ammonia concentration in the water decreased. In view of a future application of this algal biomass, due to the low total fatty acids content of 1.4 - 9.3 wt% and the high C/N ratio of 7.6 - 39.3, anaerobic digestion appeared to be the most appropriate biofuel conversion process.