Microalgal-bacterial aggregates: Applications and perspectives for wastewater treatment

Research on wastewater treatment by means of microalgal-bacterial processes has become a hot topic worldwide during the last two decades. Owing to the lower energy demand for oxygenation, the enhanced nutrient removal and the potential for resource recovery, microalgal-based technologies are nowadays considered as a good alternative to conventional activated sludge treatments in many instances. Nevertheless, biomass harvesting still constitutes one of the major challenges of microalgal-bacterial systems for wastewater treatment, which is hindered by the poor settleability of microalgal biomass. In this review, the use of microalgal-bacterial aggregates (MABAs) to overcome harvesting issues and to enhance resource recovery is presented. The fundamentals of MABAs-based technologies, the operational strategies and factors affecting the formation of MABAs, the microbiology and the methanogenic potential of the aggregates are addressed and critically discussed. The most recent findings and the challenges facing this technology towards its consolidation are also presented.