Produção de biohidrogênio por Rhodobacter capsulatus utilizando como substrato o efluente da fermentação escura

Abstract

The use of the hybrid system has been seen as an energy carrier of the future for the biohydrogen production due to its advantages. In this system, the resulting effluent from the first stage, that is the dark fermentation and rich in organic acids, is used as a substrate by non-sulfur purple bacteria in photo-fermentation step. This process has sustainability character due to the use of renewable resources, with simultaneous production of value-added product and waste removal. In this work, the production of biohydrogen in a batch process by non-sulfur purple bacteria, Rhodobacter capsulatus. The substrate used was the effluent from dark fermentation of whey permeate by microbial consortium. This effluent was centrifuged in order to separate the cells and the supernatant was adjusted according to the composition of the RCV medium without addition of ammonium sulphate and malic acid. The initial pH was adjusted to 6.8. In a first step, the experiments were performed in 50 mL penicillin bottles to verify the influence of effluent composition of dark fermentation in terms of metabolites and not converted lactose. The results of these preliminary tests have shown the necessity of providing a source of sugar for the R. capsulatus, as in the absence of lactose the H2 production was negligible. The best results were obtained in the presence of lactose and lactic acid in the concentration range of 4.4 to 8.0 and 4.6 to 14.2 g/L, respectively, favoring the production of hydrogen, with a maximum yield of 37.14 mmol H2/L.dia. Afterwards, photo-fermentation trials with scale-up (1.5 L reactor) were conducted to test the behavior of production over time. Thus, the addition of carbon sources in the process was evaluated. The sugars tested were lactose and glucose and the effect of the alternating addition of these sugars was checked as well. These results permit to conclude that there is a synergism between the effluent metabolites of dark fermentation and sugar, with the need to supplement the effluent with a second carbon source. The inoculum potential to hydrogen synthesis was higher when the process began in the presence of lactose. The highest productivity was attained by performing the process containing 9.3 g/L lactose and, subsequently, correcting the sugar concentration to 6.0 g/L by adding, alternately, lactose and glucose. In this condition, the maximum productivity was 208.4 mmol H2/L.dia and the culture could be maintained activate to hydrogen production by photo-fermentation for up to 787 h.