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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.
- Culture strategies for lipid production using low-cost carbon sources by rhodosporidium toruloidesPublication . Afonso, Valdemira; Tangerino, Laura; Oliveira, Daiana; Raposo, SaraThe development of sustainable biofuels is inserted in the biorefinery concept through the use and valorization of raw material. Volatile fatty acids (VFAs) and rich-carbon wastes, present in different raw materials, have gradually been used as the carbon source for lipid production by oleaginous yeasts. In this context, it is essential to develop practical culture strategies for oleaginous yeast to use these wastes, acetic acid and the carob industry by-product. In this study, new approaches in the cultivation of the yeast Rhodosporidium toruloides were tested, in order to maximize the accumulation of biomass and lipids. Different concentrations of carob kibbles sugar rich extract and acetic acid waste were used, as low-cost carbon sources, to select the best culture strategy for the bioconversion of these wastes into microbial oils. Microbial oils were produced by R. toruloides using 3-18 g/l acetic acid and 9-70 g/l carob extract, with different carbon-to-nitrogen ratios (C/Ns). Batch and fed-batch cultures were compared in terms of biomass and lipid production and lipid productivity. The highest biomass of 19.14 +/- 0.54 g/l was obtained in batch cultures with 70 g/l of carob extract. A lipid content of 20% (w/w) was achieved using 15 g/l of acetic acid as the carbon source in a fed-batch mode. To improve biomass production as well as lipid accumulation, the strategy used was the combination of both residues in fed-batch sequential mode of the cultures in a 2L STR bioreactor. This strategy improved the lipid yield to 40% (w/w). These results provide viable culture strategies for lipid accumulation by R. toruloides using diverse waste-derived VFA's and sugars.
- Abordagens para a acumulação de lípidos e coprodutos de elevado valor pela levedura Rhodosporidium toruloidesPublication . Afonso, Valdemira; Raposo, SaraO biodiesel de 3ª geração obtido a partir da reação de transesterificação de óleos microbianos apresenta uma alternativa viável aos combustíveis fósseis. Contudo, os custos de produção são ainda elevados impedindo a sua produção em larga escala. No presente trabalho foram desenvolvidas estratégias de cultura da levedura Rhodosporidium toruloides utilizando dois resíduos agroindustriais como fontes de carbono de baixo custo, o extrato de alfarroba e um resíduo rico em ácido acético, com o fim de otimizar a produção de biomassa e acumulação de lípidos indicados para a produção de biodiesel. Numa fase inicial, avaliou-se o crescimento da levedura em meio com o resíduo rico em ácido acético como única fonte de carbono, e definiu-se o melhor rácio C/N para a produção de biomassa e lípidos. Foram testados rácios C/N entre 60 e 70 (3-15 g/L de Ace) tendo-se obtido uma biomassa máxima de 6,41 g/L no rácio de 70. Após a realização de um fed-batch com a adição de 10 g/L de glucose obteve-se um incremento de 50% da quantidade de lípidos produzidos atingindo-se 0,49 g/L de lípidos neutros no rácio de 65. Foram comparados os dois resíduos em modo fed-batch, tendo-se observado que a produção de biomassa é favorecida no resíduo de alfarroba com 70 g/L onde se obtiveram 7,44 g/L, por outro lado, a produção de lípidos foi potenciada na cultura com resíduo de ácido acético, atingindo-se 0,55 g/L correspondendo a 20% (p/p) de lípidos acumulados. Com base nestes resultados, procedeu-se ao aumento de escala para reator STR de 2L, combinando os dois resíduos como fonte de carbono numa estratégia de fed-batch sequencial, onde se iniciou as culturas com o resíduo de alfarroba como fonte de carbono, e numa segunda fase, adicionou-se 15 g/L de resíduo de ácido acético. Conseguiu-se assim, atingir uma produção de biomassa máxima de 15 g/L e uma acumulação lipídica de 40% (p/p). Foi também traçado o perfil lipídico, no qual se observou que a conversão dos resíduos de alfarroba e ácido acético originaram um elevado teor em ácido oleico e palmítico, o que sugere que os óleos obtidos podem ser utilizados na produção de biodiesel de qualidade, com propriedades dentro dos limites estabelecidos pela Norma Europeia de Qualidade EN12412. Realizou-se ainda a extração e determinação do perfil de carotenoides, tendo-se obtido 75,58 mg/L de carotenoides totais com 55,3 % de torulorodina, 20,7% de toruleno e 20,9% de β-toruleno, resultados que indicam a possibilidade de coprodução destes compostos em simultâneo com a produção de lípidos num contexto de biorrefinaria.
- 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.