The seminar of April, was given by PhD Candidate Yolanda López.

Current wastewater treatment technologies focus on developing more efficient processes, such as those based on bacterial populations grown as granules, which have advantages over conventional activated sludge systems, like better sludge settling properties, which facilitate the biomass separation, and the ability to remove organic matter and nutrients in the same unit. However, the main drawback is the high energy consumption during aeration, which leads to unavoidable greenhouse gases emissions. On the other hand, the use of microalgae has gained relevance, as their capacity to sequester CO2 is 10 to 50 times higher than that of terrestrial plants. However, microalgae are grown in suspended culture, which implies an energy intensive biomass harvesting process to separate them from the treated water. Therefore, the combination of microalgae and bacteria forming aggregates can combine the strengths of both processes and reduce their weaknesses. In this symbiosis, the O2 required by the bacteria can be supplied by the photosynthesis of the microalgae, and the CO2 generated from bacterial respiration can be used for microalgal metabolism. At the same time, they grow together forming aggregates that facilitate the separation between the biomass (consortia microalgae-bacteria) and the recovered clean water. These aggregates are called photogranules. Photogranules have been applied to wastewater treatment, achieving efficient pollutant removal without aeration, but their application has been restricted to low organic and nitrogen loads or long hydraulic retention times (HRT).

This study carried out by Yolanda in the frame of ALBA project aimed to evaluate the limits of aeration reduction in photogranular systems under conditions typically applicable to aerobic granular sludge (high carbon and nitrogen loads at short HRT).