These two international conferences bring together scientists, algaeneers and practitioners to exchange the latest knowledge on the application of photosynthetic microorganisms for wastewater treatment and resource recovery, covering traditional opened ponds systems and the use of photobioreactors. Wastewater engineers using photosynthetic microorganisms can benefit from knowledge coming from the use of algae to produce biofuels, food supplements or green pharmaceuticals and of purple photosynthetic bacteria. Likewise, wastewater as a cheap source of nutrients and inorganic carbon is promising for the mass production of algae-based commodities. For example, microalgae based treatment systems in developing and tropical countries may reduce wastewater treatment costs via the recovery of its inherent resources, while providing effective sanitation services. The opportunity to bring together expertise in both extensive (ponds) and intensive (photobioreactors) algal systems in a single event constitutes an unique overview and discussion platform of the latest scientific developments and practical applications in a field of research that has exponentially increased over the past decade. In this context, it is worth noticing that the number of publications in microalgae-based wastewater treatment increase from 60 in 2007 to > 1000 in 2017.