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- Biogas production from microalgal biomass produced in the tertiary treatment of urban wastewater: assessment of seasonal variationsPublication . Barros, Raúl; Raposo, Sara; Morais, Etiele; Rodrigues, Brígida; Lourenço Afonso, Valdemira; Gonçalves, Pedro; Marques, José; Cerqueira, Ricardo; Varela, João; Ribau Teixeira, Margarida; Barreira, LuísaThe valorization of microalgal biomass produced during wastewater treatment has the potential to mitigate treatment costs. As contaminated biomass (e.g., with pharmaceuticals, toxic metals, etc.) is often generated, biogas production is considered an effective valorization option. The biomass was obtained from a pilot facility of photobioreactors for tertiary wastewater treatment. The pilots were run for one year with naturally formed microalgal consortia. The biogas was generated in 70 mL crimp-top vials at 35 °C, quantified with a manometer and the methane yield measured by gas chromatography. A maximum biogas production of 311 mL/g volatile solids (VS) with a methane yield of 252 mL/g VS was obtained with the spring samples. These rather low values were not improved using previous thermo-acidic hydrolysis, suggesting that the low intrinsic biodegradable organic matter content of the consortia might be the cause for low yield. Considering the total volume of wastewater treated by this plant and the average amount of methane produced in this study, the substitution of the current tertiary treatment with the one here proposed would reduce the energy consumption of the plant by 20% and create an energy surplus of 2.8%. The implementation of this system would therefore contribute towards meeting the ambitious decarbonization targets established by the EU.
- Alternative chemo-enzymatic hydrolysis strategy applied to different microalgae species for bioethanol productionPublication . Constantino, Ana; Rodrigues, Brígida; Leon, R.; Barros, Raúl; Raposo, SaraMicroalgae have been considered third generation feedstock for biofuel production based on the expectation that large amounts of algal biomass can be cultivated at an acceptable cost. Transformation of biomass into ethanol requires a saccharification step, where complex carbohydrates are broken down by hydrolysis into sugars that can be fermented to bioethanol. Carbohydrate mobilization is hampered by the recalcitrance of the cell envelope of microalgal cells, because complex structural polysaccharides are difficult to depolymerize and make internal carbohydrate reserves inaccessible to hydrolysis. Saccharification can be accomplished by either acidic hydrolysis, enzymatic treatment or a combination of both. The present work focused on the chemo-enzymatic hydrolysis of lyophilized biomass of different microalgae and subsequent fermentation of hydrolysates with higher reducing sugar content. A chemo-enzymatic hydrolysis strategy was defined, consisting of an acid pretreatment carried out at high pressure and temperature, followed by incubation with Amyloglucosidase and finally by incubation with alpha-Amylase, the opposite order of the conventional use of these enzymes. An increase of reducing sugar yield of about one third was observed, and this strategy was successfully applied to a broad group of microalgae, resulting in maximum release yields of at least 34.0 +/- 1.0 g total reducing sugar/100 g dry biomass. For bioethanol production studies, the microalgae hydrolysates of Chlorella sorokiniana, Tetraselmis sp. (Necton) and Skeletonema sp. were selected according to their high reducing sugar content. High ethanol production was achieved with all hydrolysates, with ethanol yields close to the theoretical maximum and the highest ethanol concentrations so far reported under comparable conditions. Chlorella sorokiniana stood out as the best hydrolysate for ethanol production, with an ethanol yield of 0.464 +/- 0.013 g/g reducing sugar and ethanol productivity of 0.344 +/- 0.020 g/L.h.
- Scale-up and large-scale production of Tetraselmis sp CTP4 (Chlorophyta) for CO2 mitigation: from an agar plate to 100-m(3) industrial photobioreactorsPublication . Pereira, Hugo; Paramo, Jaime; Silva, Joana; Marques, Ana; Barros, Ana; Mauricio, Dinis; Santos, Tamara; Schulze, Peter; Raul J Barros; Gouveia, Luisa; Barreira, Luísa; Varela, J.Industrial production of novel microalgal isolates is key to improving the current portfolio of available strains that are able to grow in large-scale production systems for different biotechnological applications, including carbon mitigation. In this context, Tetraselmis sp. CTP4 was successfully scaled up from an agar plate to 35-and 100-m(3) industrial scale tubular photobioreactors (PBR). Growth was performed semi-continuously for 60 days in the autumn-winter season (17th October -14th December). Optimisation of tubular PBR operations showed that improved productivities were obtained at a culture velocity of 0.65-1.35 m s(-1) and a pH set-point for CO2 injection of 8.0. Highest volumetric (0.08 +/- 0.01 g L-1 d(-1)) and areal (20.3 +/- 3.2 g m(-2) d(-1)) biomass productivities were attained in the 100-m(3) PBR compared to those of the 35-m(3) PBR (0.05 +/- 0.02 g L-1 d(-1) and 13.5 +/- 4.3 g m(-2) d(-1), respectively). Lipid contents were similar in both PBRs (9-10% of ash free dry weight). CO2 sequestration was followed in the 100-m(3) PBR, revealing a mean CO2 mitigation efficiency of 65% and a biomass to carbon ratio of 1.80. Tetraselmis sp. CTP4 is thus a robust candidate for industrial-scale production with promising biomass productivities and photosynthetic efficiencies up to 3.5% of total solar irradiance.
- Biofuels production by chlorella sorokiniana in a biorefinery perspectivePublication . Constantino, Ana; Glória, Patrícia; Rodrigues, Brígida; Leon, Rosa; Barros, Raúl; Raposo, SaraBiofuels Production By Chlorella Sorokiniana In A Biorefinery Perspective (Poster Presentation) in Abstract Book 5th Algaeurope Conference
- From lignocellulosic residues to protein sources: insights into biomass pre-treatments and conversionPublication . Vera dos Anjos, Isabela; Coelho, Natacha; Duarte, Hugo; Proença, Diogo Neves; Duarte, Maria F.; Jorge de Barros, Raúl José; Raposo, Sara; Gonçalves, Sandra; Romano, Anabela; Medronho, BrunoWith the global population steadily rising, the demand for sustainable protein sources has become increasingly urgent. Traditional animal- and plant-based proteins face challenges related to scalability, resource efficiency, and environmental impact. In this context, single-cell protein has emerged as a promising alternative. Derived from microorganisms such as algae, bacteria, fungi, and yeast, single-cell protein offers a high nutritional profileincluding all essential amino acids and vitamins—while enabling rapid production, minimal land and water requirements, and no generation of greenhouse gas emissions. A particularly compelling advantage of single-cell protein is its ability to be produced from agro-industrial waste, converting low-cost residues into valuable nutritional resources and contributing to environmental sustainability. Among these waste streams, lignocellulosic biomass from agricultural and forestry residues stands out as a renewable, biodegradable, and abundant feedstock. This review explores the potential of lignocellulosic waste as a substrate for single-cell protein production, emphasizing both its environmental advantages and nutritional value. It highlights the single-cell protein role as a sustainable and scalable alternative to conventional protein sources. The review also identifies key scientific, economic, and regulatory challenges, and recognizes the importance of targeted investments, particularly in policy development, public awareness, and technological innovation, to enable the broader adoption and acceptance of single-cell protein -based products.
- The potential of native microalgae consortia to remove pharmaceutical compounds present in treated wastewaterPublication . Lourenço Afonso, Valdemira; Rodrigues, Brígida; Borges, Rodrigo; Jorge de Barros, Raúl José; Bebianno, Maria; Raposo, SaraWastewater treatment plants play a key role in the release of pharmaceuticals and other contaminants into the aquatic environment, causing negative effects on the ecosystems of receiving water bodies. This work aimed to assess the removal efficiency of real loads of these contaminants by wastewater-native microalgae consortia acting on treated wastewater previously subjected to secondary treatment. Wastewater sampling and removal efficiency experiments were conducted over 1 year at three different sampling points. Nineteen pharmaceutical compounds of different drug classes (stimulants, anticonvulsants, antidepressants, antibiotics, β-blockers, lipid regulators, and nonsteroidal anti-inflammatory drugs/analgesics), as well as one herbicide/algicide (Diuron) were detected and quantified. Native blooming microalgae consortia were grown in treated wastewaters, and their potential to remove these compounds was quantified. The removal efficiency of these compounds by native microalgae consortia was variable, ranging from almost no removal for Clofibric acid or Ketoprofen to near complete removal for Fluoxetine, Venlafaxine, Atenolol or Diuron. These variations were influenced not only by the molecular nature of the compounds but also by the microbial composition variability of the microalgae consortia, especially among the prokaryotes present. Overall, microalgae consortia successfully removed between 40 % and 83 % of the total detected compounds, preventing a significant part of these from entering the aquatic environment, contributing to enhance treated wastewater quality. Significant biomass growth was observed, reaching dry-weight concentrations up to 2.6 g.L− 1 , indicative of good capacity of the grown consortia to deal with the toxicity effects of the pollutants. In addition to what is now reported, microalgae treatment also removes other pollutants, such as nutrients, metals or microplastic particles, constituting a versatile tertiary treatment for polishing treated wastewaters. These findings demonstrate the potential of native microalgae consortia-based systems to improve wastewater treatment processes, mitigating the environmental impact of pharmaceutical compounds while producing potentially useful biomass.