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- Municipal and industrial wastewater blending: Effect of the carbon/ nitrogen ratio on microalgae productivity and biocompound accumulationPublication . Pereira, Alexia Saleme Aona de Paula; Magalhães, Iara; Silva, Thiago; Reis, Alberto; de Aguiar do Couto, Eduardo; Calijuri, Maria LuciaABSTRACT: Municipal wastewater (MW) and industrial wastewater from juice processing (IWJ) were blended in different proportions to assess the effect of the carbon/nitrogen (C/N) ratio on pollutant removal, microalgal biomass (MB) cultivation, and the accumulation of carotenoids and biocompounds. MB development was not observed in treatments with higher C/N ratios (>30.67). The wastewater mixture favored the removal of dissolved organic carbon (75.61 and 81.90%) and soluble chemical oxygen demand (66.78-88.85%), compared to the treatment composed exclusively of MW (T7). Treatments T3 and T6 (C/N ratio equal to 30.67 and 7.52, respectively) showed higher Chlorophyll-a concentrations, 1.47 and 1.54 times higher than T7 (C/N ratio 1.75). It was also observed that the C/N ratio of 30.67 favored the accumulation of carbohydrates and lipids (30.07% and 26.39%, respectively), while the C/N ratio of 7.52 improved protein accumulation (33.00%). The fatty acids C16:0, C18:1, C18:2, and C18:3 had the highest concentrations. Additionally, increasing the C/N ratio can be an efficient strategy to improve the production of fatty acids for biofuels, mainly due to the increased concentration of shorter-chain fatty acids (C16:0). These findings suggest that blending wastewater not only enhances treatment performance but also increases the accumulation of valuable carbohydrates and lipids in MB, and optimizes fatty acid production for biofuel applications. This research represents significant progress towards feasibility of using MB produced from wastewater.
- Enhancing microalgae biomass production: Exploring improved scraping frequency in a hybrid cultivation systemPublication . Silva, Thiago; Pereira, Alexia Saleme Aona de Paula; Ferreira, Jessica; Lorentz, Juliana F.; de Assis, Marilia Luise; Assemany, Paula; Reis, Alberto; Calijuri, Maria LuciaABSTRACT: Recently, hybrid systems, such as those incorporating high-rate algal ponds (HRAPs) and biofilm reactors (BRs), have shown promise in treating domestic wastewater while cultivating microalgae. In this context, the objective of the present study was to determine an improved scraping frequency to maximize microalgae biomass productivity in a mix of industrial (fruit-based juice production) and domestic wastewater. The mix was set to balance the carbon/nitrogen ratio. The scraping strategy involved maintaining 1 cm wide stripes to retain an inoculum in the reactor. Three scraping frequencies (2, 4, and 6 days) were evaluated. The findings indicate that a scraping frequency of each 2 days provided the highest biomass productivity (18.75 g total volatile solids m(- 2) d(-1)). The species' behavior varied with frequency: Chlorella vulgaris was abundant at 6-day intervals, whereas Tetradesmus obliquus favored shorter intervals. Biomass from more frequent scraping demonstrated a higher lipid content (15.45%). Extrapolymeric substance production was also highest at the 2-day frequency. Concerning wastewater treatment, the system removed 93% of dissolved organic carbon and similar to 100% of ammoniacal nitrogen. Combining industrial and domestic wastewater sources to balance the carbon/nitrogen ratio enhanced treatment efficiency and biomass yield. This study highlights the potential of adjusting scraping frequencies in hybrid systems for improved wastewater treatment and microalgae production.
- Bio-oil from hydrothermal liquefaction of microalgae cultivated in wastewater: An economic and life cycle approachPublication . Silva, Thiago; Junior, Maurino Magno de Jesus; Magalhães, Iara; Ananias, Marina Stefany; Saleme Aona de Paula Pereira, Alexia; Rodrigues, Fábio de Ávila; Delgado dos Reis, Alberto José; Calijuri, Maria LuciaABSTRACT: Although microalgae are a promising sustainable biofuel feedstock, their energy-intensive production and most environmental assessments rarely achieve the desired trade-off between productivity and sustainability. In this context, this study aims to evaluate the economic and environmental feasibility of producing bio-oil via hydrothermal liquefaction (HTL) of wastewater-grown microalgae at an industrial scale. Four scenarios varied production scale and steam source: sugarcane bagasse (SCB) in SC1 and SC3, liquefied petroleum gas (LPG) in SC2 and SC4. Each scenario processed microalgae at 300 degrees C for 30 min. Smaller-scale feedstock (1332.9 kg/h) in SC1 and SC2 produced 34.6 kg/h of bio-oil, while the larger feedstock (85,554.4 kg/h) in SC3 and SC4 yielded 2222.2 kg/h. Microalgae biomass cultivation costs dominated overall expenses (56-75 %). Economic analyses indicated minimum selling prices of 3.82-8.52 USD/kg, exceeding the average literature figure of 1.57 USD/kg. Life Cycle Assessment (LCA) showed SCB reduced fossil resource depletion by 14.97 % compared to LPG but increased emissions of nitrogen oxides, particulates, and toxic compounds, which are manageable via selective catalytic reduction and flue gas desulphurization. Cyclohexane as a solvent elevated human carcinogenic toxicity, greener alternatives could reduce toxicity but may cost more, requiring further cost analysis. Advancing this biorefinery route requires optimization of cultivation and processing costs, adoption of environmentally benign solvents, and implementation of emission control strategies to enable economically feasible and environmentally sustainable bio-oil production.
- Shining a light on outdoor algal systems for wastewater treatment: How artificial light enhancement impacts biomass costs and life cyclePublication . Magalhães, Iara; Jesus Junior, Maurino Magno; França, Bruna Thomazinho; Silva, Thiago; Saleme Aona de Paula Pereira, Alexia; Souza, Lucas Cescon de Almeida; Rodrigues, Fábio de Ávila; Reis, Alberto; Peixoto Assemany, Paula; Calijuri, Maria LuciaABSTRACT: Microalgae-based wastewater treatment is increasingly viewed as a cleaner production strategy, combining nutrient removal and biomass generation for high-value applications. However, productivity constraints remain a critical barrier to broader implementation. This study examines the viability of integrating light-emitting diodes (LEDs) into outdoor bubble column reactors for domestic wastewater treatment and biomass production, focusing on environmental impacts and techno-economic performance. Three lighting regimes—natural light only (control), 12-h LED cycles, and 24-h LED cycles—were experimentally evaluated and scaled up using Aspen Plus® simulation. Life cycle assessments (LCA) were conducted to quantify environmental impacts (ReCiPe, 2016 method), and a detailed techno-economic analysis determined minimum biomass selling prices. Compared to the control, LED-assisted systems increased biomass yields by 24–34 %, yet capital and operational costs offset productivity gains. Under grid electricity, minimum selling prices considering capital and operational costs ranged from 80.76 to 91.37 USD/kg for LED systems versus 68.85 USD/kg for the control. Photovoltaic (PV) integration reduced operational costs by up to 16.89 %, but LED scenarios remained more expensive. LCA findings highlighted substantially higher environmental impacts (78–149 times) for LED systems, partly alleviated by PV-powered operations. Sensitivity analysis identified nutrient availability, process scale, and reactor costs as pivotal factors influencing the feasibility of LED-enhanced wastewater treatment. Overall, while LED technology offers notable productivity benefits, its economic and environmental trade-offs underscore the need for integrated approaches—ranging from material innovations to policy incentives—to achieve truly sustainable wastewater-based microalgal production.
- Pilot-Scale cultivation of microalgae in blended effluents: C/N ratio management to boost biomass and biofuel precursorsPublication . Saleme Aona de Paula Pereira, Alexia; Silva, Thiago; Magalhães, Iara; Santos, Weller Gabriel da Silva; Oliveira, Mateus Soares de; Reis, Alberto; Couto, Eduardo de Aguiar; Calijuri, Maria LuciaABSTRACT: Algal biotechnology offers a sustainable pathway for wastewater treatment and resource recovery. However, the low carbon-to-nitrogen (C/N) ratio in domestic wastewater often limits microalgal productivity, which may compromise process viability and, consequently, limit its application in bioproduct valorization routes. This study evaluated the effects of blending municipal wastewater (MW) with industrial wastewater from juice processing (IWJ) at different ratios on biomass production, biochemical composition, and pollutant removal. Pilot-scale experiments in outdoor high-rate algal ponds, operated without external carbon dioxide (CO2) supply (relying on inorganic carbon present in the wastewater and passive diffusion from air). These experiments tested three blends: T1 (60 % MW + 40 % IWJ, C/N 9.25), T2 (40 % MW + 60 % IWJ, C/N 25.31), and T3 (20 % MW + 80 % IWJ, C/N 52.71). T1 achieved the highest biomass productivity and lipid content (14.44 %, p < 0.05), while T3 presented the highest levels of saturated fatty acids C16:0 (40.39 %) and C18:0 (10.08 %), supporting its biodiesel potential. Carbohydrate accumulation was enhanced in T2 (18.44 %) and T3 (21.09 %) under nitrogen-limited conditions. Microalgal species composition varied significantly with the C/N ratio, indicating selective adaptation. Additionally, dissolved organic carbon removal followed first-order kinetics across treatments, confirming model applicability. These findings underscore the effectiveness of effluent blending and C/N adjustment to enhance biomass quality, pollutant removal, and suitability for biofuel production in integrated algal-based wastewater treatment systems.
- Modulating microalgal metabolism and its integration into dark fermentation: Challenges and opportunities with wastewater-grown biomassPublication . Ferreira, Jessica; Silva, Thiago; Saleme Aona de Paula Pereira, Alexia; Reis, Alberto; Zaiat, Marcelo; ; Calijuri, Maria LuciaABSTRACT: Microalgae represent a promising feedstock for the sustainable production of bioproducts and bioenergy, due to their versatile biochemical composition and environmental adaptability. Given the wide range of bioproducts that can be derived from their biomass, its biochemical composition suggests more favorable conversion routes and can be enhanced through cultivation conditions focused on the synthesis of one (or more) metabolites of interest to the biotechnology market. Accordingly, this review focuses on approaches for modulating microalgal metabolism, such as nutrient depletion and reactor configuration characteristics, among others, as well as on key outcomes obtained through two-stage cultivation, which combine phases of high biomass and metabolite productivity. From a resource recovery perspective, emphasis was placed on approaches that are more readily applicable to wastewater treatment plants. Furthermore, as energy-oriented routes are more suitable for valorizing of biomass grown in wastewater and considering that biohydrogen has been shown to be an emerging product of scientific relevance, this review also analyzes the limitations and strategies for integrating its production via dark fermentation. Pretreatment techniques and co-fermentation approaches were discussed as strategies to overcome the challenges associated with the anaerobic fermentation/digestion of microalgae due to their characteristics and biochemical composition. Finally, biorefinery configurations that integrate these processes were discussed from a scale-up perspective.