Microalgal biomass is increasingly gaining interest in new emerging sectors such as biogas and biodiesel production, animal and aqua feed, biopesticides, pharmaceuticals and biofertilizers. Apart from biomass production, starting from the 1960s, microalgae were studied as a new water remediation technology, with the advantage of guaranteeing fewer greenhouse gas production, less energy demand and costs, and less production of residues (i.e., sludge). Moreover, the coupling with wastewater treatment can be considered a cost-effective algal production, as the nutrients necessary for the microalgal growth come directly from the wastewater and do not have to be provided by chemicals or fertilizers. In sewage, microalgae live together with bacteria typically classified as nitrifying and heterogenic. Thanks to their synergy, it is possible to guarantee the degradation of organic matter and the recovery of nitrogen and phosphorous. In a few words, microalgae produce the oxygen that is used by bacteria, while bacteria degrade the organic matter and produce the organic carbon necessary for microalgal life; moreover, two different groups of nitrifying bacteria (ammonia-oxidizing bacteria and nitrite-oxidizing bacteria) enhance the nitrogen recovery, using the ammonia (NH 4 + ) and transforming it into NO 3 , used by microalgae.
Although the potentiality of this remediation process is already proven at laboratory scale, the process still needs to be further optimized in terms of productivity and nutrient recovery at pilot and industrial scale dimensions, as it still is facing challenges related to costs and efficiency. The most used design for wastewater treatment is the open pond, which ensures low capital investment and easy maintenance, permitting the treatment of high water volumes thanks to its high volume-to-surface ratio. However, this technology allows a narrow control of the most impacting parameters, since the system is exposed to culture contamination, and variables like light and temperature continuously change based on the weather variation. Apart from developing successful technology for biomass production, further optimization needs to be performed for the other process parameters that can be regulated, such as pH, levels of oxygen dissolved, culture level, and harvest/dilution strategy. Therefore, it is fundamental to study their impact on the culture performance and the microalgae-bacteria equilibrium to define the optimum conditions for nutrient recovery and the process remediation efficiency. This objective can be carried out by optimization analysis in large-scale systems, permitting the provision of valuable information and further leading future work to enhance process optimization and automation. Moreover, mathematical modeling proves to be a very powerful tool because it provides a process description depending on the process parameters and also allows to perform simulations (to better understand the process) and the implementation of advanced control strategies.
The objective of the research project at the University of Almeria, under the supervision of Prof. Gabriel
Acién and Prof. José Luis Guzmán, is to optimize and model microalgae wastewater treatment processes. The project will be carried out outdoors in pilot-scale raceways reactors available in the pilot plant of the University of Almeria. In these facilities, optimization analysis and development of new control strategies and new virtual sensors for culture monitoring and control will be done. Moreover, mathematical models will be developed allowing to describe the microalgal growth and the remediation efficiency and permitting the implementation of simulation tools.