# ABACO: A New Model of Microalgae-Bacteria Consortia for Biological Treatment of Wastewaters
## 3 Results
### Discussion  
The combination of microalgae biomass production processes and wastewater (diluted pig slurry) treatment is a cost-effective goal that poses several challenges. On the one hand, the already used wastewater contains high amounts of nutrients that allow microalgae and bacteria growth [27]. On the other hand, the lower energy demand for the microalgae-bacteria wastewater treatment, along with the ability of microalgae for CO\({}_{2}\) fixation, significantly increases the environmental sustainability of this eco-friendly technology [28]. Apart from multiple biological models proposed for microalgae-bacteria wastewater treatment using different types of effluents, scarce information is available about the use of animal manure as a nutrient source [29]. In this work, an integral microalgae and bacteria model named ABACO was developed, calibrated, and validated with experimental data from duplicate laboratory-scale photobioreactors using pig slurry as a nutrient source. The implementation of the model allowed us to simulate the dynamics of different components in the system and the relative proportions of microalgae and bacteria. The values of several model parameters were calibrated using genetic algorithms. Addi  
Figure 8: The microbial percentages obtained during the calibration process, the validation process, and the experimental respirometric measurements.  
tionally, the percentage of each microbial population present in the microalgae-bacteria culture was estimated.  
The results obtained from the comparison between the estimated values with respect to the measured experimental data have been satisfactory. The concentrations of the elements were adjusted within the range formed by the measurement points, despite being scattered data. The percentages of microalgae and bacteria within the reactor over time showed values close to those obtained in the literature [17; 29]. Additionally, these percentages were estimated by a respirometric method, in which the microalgae, heterotrophic bacteria, and nitrifying bacteria showed estimated values that were close to those determined by calibration and validation processes. When analyzing the errors obtained for both cases, it becomes clear that faithfully estimating the evolution in the concentration of the different elements in the reactor is a complex process. The experimental values are very scattered, and that hinders their continuous evolution estimation. Even so, the results obtained are within the ranges of variation of the measurements taken.  
The complexity in measuring individual concentrations of each species highlights the need for a reliable estimation method. Due to the calibration using genetic algorithms, it is possible to estimate the percentage of each microorganism in the reactor. From experimental data, the model allows one to determine the initial percentage of each element and estimate its evolution over time. In this way, the model can act as a simulator to predict the behavior of organisms based on the concentrations of nutrients present in the reactor medium. This model and the calibration parameters obtained will serve as the basis for the development of simulation models where the production of microalgae biomass is combined with wastewater treatment.