the water sector needs a paradigm shift from a focus on water treatment and supply, collection and from focusing on the treatment and supply of water, the collection and treatment of wastewater to meet discharge limits, and the processing of the wastes from these operations, to focus on integrated management that waste from these operations, and to focus instead on integrated management that enables a circular water economy with minimal emissions. This change of vision means that the traditional «wastewater treatment plants» are now seen as «water resource recovery and regeneration centres». From a technological point of view, new developments developments should focus on process intensification, resource recovery and the design of systems that resource recovery and the design of systems that allow high effluent qualities with minimum of emissions, or even achieving carbon neutrality. 

Examples of such new technologies include advanced anaerobic digestion processes, such as advanced anaerobic digestion processes developed in membrane bioreactors,

the biological removal of nutrients by means of granular biomass (a process commercially known as Nereda®), the removal of ammonium by partial nitrification followed by a partial nitrification following an anammox process or photobiological systems, based on microalgae and cyanobacteria.

Microalgae can remove nitrogen, phosphorus and organic matter from wastewater and transform it into biomass. In this regard, the joint use of bacteria and microalgae for wastewater treatment has recently attracted the attention of many researchers. Microalgae-based wastewater treatments have emerged in recent years as a potential substitute for conventional treatments, due to their economic and environmental sustainability.