Biorrefinaria de microalgas e valoração de efluentes industriais: um modelo potencial de bioeconomia circular para o Brasil

Abstract

In recent years, human demand for natural resources has exceeded the planet's regenerative capacity, necessitating a shift from the linear economic model of "extract, produce, discard." In this context, the microalgae biorefinery associated with wastewater treatment (MBWT) emerges as a promising model of circular bioeconomy, aligning with major global sustainability agendas and holding significant potential to integrate into Brazil's recent neo-industrialization program. Although microalgae have gained prominence in recent years as a technological solution for industrial wastewater treatment, there remains a lack of studies focused on the simultaneous utilization of intra- and extracellularly synthesized bioproducts. This study aims to provide a comprehensive and innovative perspective on biomass, high-value extracellular products, and the environmental benefits of MBWT concerning produced water (PW), cassava wastewater (CW), and whey (W). To achieve this objective, the thesis is structured into five methodological pillars: (i) global technological and market prospecting in this research field; (ii) characterization of effluents and acclimatization of Chlorella vulgaris to them; (iii) study of the influence of pre-treatment and supplementation of PW on intra- and extracellular microalgal bioproducts; (iv) optimization of microalgae cultures for the individual and simultaneous production of biomass and extracellular polymeric substances (EPS); (v) pilot- scale cultures containing W and analysis of the microalgae-bacteria consortium in EPS production and the rheological potential of these biopolymers. The global market panorama, supported by the technological S-curve, shows that MBWT has been an emerging area since 2011. From the state-of-the-art analysis, five barriers to microalgae cultivation in PW were identified, which were mitigated with some form of pre-treatment and/or supplementation. From a kinetic perspective, pre-treatment with activated carbon (AC) only worked when accompanied by CW supplementation, resulting in maximum biomass productivity. Additionally, the produced biodiesels met national and international standards. Morphological evaluation of the extracellular medium revealed the presence of chelated microparticles in a polymeric matrix, forming a biocomposite (EPS-microparticles) with potential application as a viscosifying additive for the petroleum industry. AC pre-treatment, along with supplementation, promoted greater synthesis of these biocomposites with better rheological properties, achieving a production of 1.16 g L−1 and an average size distribution of 0.7 μm. Global desirability analysis indicated that the combination of 10% CW, 38% PW, and 170 rpm agitation simultaneously maximized EPS and biomass productions, with predictions of 1.89 and 1.45 g L−1, respectively, achieving a desirability of 89%. Notably, the effluent mixture (PW and CW) provided the highest EPS values reported in the literature for Chlorella vulgaris, demonstrating itself as an innovative strategy for maximizing this biopolymer. Fourier- transform infrared spectroscopy (FTIR), diffusion nuclear magnetic resonance (NMR) technique, and rheological study revealed that the biopolymers synthesized at pilot scale with W exhibited chemical and rheological characteristics comparable to commercial xanthan gum, with molecular sizes between 284 and 324 kDa. The presence of a microalgae-bacteria consortium resulted in higher EPS production and better rheological properties compared to the control, representing a significant advancement in the field of waste valorization by microalgae. Finally, this study demonstrates that MBWT contributes to environmental sustainability and offers a viable technical approach for producing high-value bioproducts, reusable in the effluent-supplying industries or other market segments, within a circular perspective. Brazil, with its intrinsic vocation for biorefineries, can incorporate MBWT as a technology within the proposal of the New Industry Brazil, taking advantage of the geopolitical context demanding new green solutions. This technology transforms industrial wastewater management, converting waste into valuable resources, and adhering to the latest global sustainability agenda.