Optimization and qualitative comparison of two vinasse pre-treatments aiming at microalgae cultivation / Otimização e comparação qualitativa de dois pré-tratamentos da vinhaça visando ao cultivo de microalgas

ABSTRACT The cultivation of microalgae is a possible destination for vinasse, a residue from the sugar and alcohol industry. This use can help reduce the costs of microalgae production and remediate this residue rich in nutrients. However, the physicochemical characteristics of vinasse limit its use for microalgae growth at low concentrations, except when the residue is pretreated. This work aimed at optimizing the vinasse pretreatments of centrifugation and adsorption by smectite clay and activated charcoal on laboratory scale in terms of amounts of materials used and time spent, making them more viable on larger scales. The optimized processes were then compared in productive, economic, and environmental terms. The dilution of treated vinasse with distilled water resulted in similar growth of Chlorella vulgaris to those obtained with the dilution in BG11 medium, indicating that the addition of nutrients in culture media is not necessary. Although microalgae growth occurs in higher concentrations of vinasse treated by adsorption, the results show that centrifugation required less processing time, has cheaper processing costs, and generated much less residue. Centrifugation treatment has greater economic and environmental viabilities and was more sustainable than the adsorption, even though the algae did not grow in the centrifuged residue in concentrations as high as it did after the adsorption treatment. Therefore, this article brings a new view about the economic and environmental aspects on the use of pretreated vinasse for microalgal growth, giving a lucrative destination for a highly polluting waste.

RESUMO O cultivo de microalgas é um possível destino para a vinhaça, um resíduo da indústria sucroalcooleira. Esse uso pode ajudar a reduzir custos da produção de microalgas, além de remediar esse resíduo rico em nutrientes, entretanto as características físico-químicas da vinhaça limitam seu uso para o crescimento de microalgas a baixas concentrações, exceto quando o resíduo é pré-tratado. Este trabalho objetivou otimizar os pré-tratamentos da vinhaça de centrifugação e de adsorção por argila esmectita e carvão ativado em escala laboratorial quanto à quantidade de materiais utilizados e tempo gasto, tornando-os mais viáveis em escalas ampliadas. Os processos otimizados foram então comparados em termos produtivos, econômicos e ambientais. A diluição das vinhaças tratadas com água destilada resultou em crescimento de Chlorella vulgaris semelhante ao obtido com diluições com meio BG11, indicando que a adição de nutrientes nos meios de cultura não é necessária. Embora o crescimento de microalgas ocorra em concentrações mais altas de vinhaça tratada por adsorção, os resultados mostram que a centrifugação exigiu menos tempo de processamento, tem custos mais baratos e gerou menos resíduos. De maneira comparativa, o tratamento por centrifugação possui maior viabilidade econômica e ambiental e foi mais sustentável do que a adsorção, embora as algas não tenham crescido no resíduo centrifugado em concentrações tão altas quanto após o tratamento de adsorção. Portanto, este artigo traz uma nova visão sobre os aspectos econômicos e ambientais do uso da vinhaça pré-tratada para o crescimento de microalgas, proporcionando um destino lucrativo para um resíduo altamente poluente.

Potential effects of fungicide and algaecide extracts of Annona glabra L. (Annonaceae) on the microalgae Raphidocelis subcapitata and on the oomycete Pythium

ABSTRACT Annona glabra L. is a semi-deciduous tree that contains several active substances, including secondary metabolites, with antifungal activity. Phytopathogenic strains of the genus Pythium cause billion dollar losses all over the world on natural and crop species. Searching for eco-friendly algaecides and fungicides, we analyzed the effects of acetone extracts of A. glabra leaves on the algae Rhaphidocelis subcapitata (Korshikov) and on the oomycete Pythium aphanidermatum (Edson). We evaluated ten extract concentrations for each organism - 0 to 400 mg L-1 for algae and 0-1000 µg disc1 for oomycete. The results showed no effect on algae up to 75 mg L-1, but a significant inhibitory effect at 125 mg L-1 and above, which reduced the growth rate and the final biomass of the algae. Extract concentrations above 200 mg L-1 were completely inhibitory. The half maximal inhibitory concentration for 72 and 96 h of exposure to our crude extracts are comparable to those obtained with commercial fungicides and herbicides used in aquatic ecosystems. The P. aphanidermatum inhibition concentrations have effects comparable to fungicides as Cycloheximide and Bifonazole. Some substances isolated from the extracts are described as antifungals, which could explain part of anti-oomycete activity. Our results highlight the importance of searching bioactive compounds from plants.