Aplicação de estratégias para otimização do processo de tratamento avançado de soro do leite em reator aberto por microalgas

Abstract

Whey, a by-product of dairy processing, poses a challenge that necessitates effective treatment methods. Various strategies have been employed to address these concerns, including aerobic and anaerobic biological processes, which are deemed promising alternatives. The technology of biological treatment, particularly through the utilization of microalgae, especially during tertiary (advanced) treatment, emerges as a promising option owing to its efficiency in removing organic compounds, notably residual nitrogen, and phosphorus from the secondary (primary) treatment process, with reduced operational costs. In this context, the present study aims to analyze the whey treatment process by microalgae targeting the removal of chemical oxygen demand (COD), nitrogen (TN) and phosphorus (TP), aiming for compliance with discharge standards mandated by legislation, applying strategies for process optimization (treatment time, semi-continuous mode, co-cultivation with filamentous fungus, and utilization of 1.5 vvm aeration). The experiment was conducted using the microalgae Tetradesmus obliquus, as well as co-cultivation with the filamentous fungus Cunninghamella echinulata, combined with forced aeration in semi-continuous mode in an open reactor. Two organic loads, C1 and C2 (~ COD = 550 and 2200, TN =15 and 60, and TP = 5 and 20 mg.L-1, respectively), were employed, thus designating the experiments with the microalgae as CM1 and CM2, and for the co-cultivation with fungus as CMF1 and CMF2. It was evident that the consortium exhibited greater stability and higher efficiency in contaminant removal compared to the treatment system containing only the microalgae, at both volumetric replacement rates of 40 and 60%, whereas only 40% were viable when the microalgae were used alone. Regarding the residual COD concentration, CMF1 showed a COD variation in the range of 62 to 88 mg.L-1, remaining within the limits established by the European Union standard (125 mg.L-1), while CMF2 obtained a residual COD between 165-250 mg.L-1, requiring another treatment stage to meet the discharge standards; however, treatment efficiency was high in both cases (> 70%). With respect to total nitrogen, both organic loads CMF1 and CMF2 achieved residual concentrations between 2-10 mg.L-1, complying with the discharge standards of European legislation (10 mg.L-1). Finally, for total phosphorus, like what occurred with COD, CMF1 was efficiently treated, with residual concentrations between 0.65-0.9 mg.L-1 meeting European legislation (between 1-2 mg.L-1), while for CMF2, residual values ranged between 2-3.5 mg.L-1, indicating the need for additional treatment. The obtained dry cell weight varied between 300-900 mg.L-1 and can be utilized for biotechnological applications. Lastly, during co-cultivation, there was greater system buffering with less pH variation, ensuring greater system stability and easier adjustment compared to the system containing only the microalgae. In this context, it is relevant to note that the treatment successfully met the discharge standards established by legislation. However, it is important to emphasize the significance of validating these results on a larger scale and seeking optimization of operational parameters.