The Portuguese researchers from University of Beira Interior and from the Center of Biotechnologies for Agriculture and Food Industry CEBAL together with their colleagues from Technical University of Denmark tested the technology of receiving hydrogen from winery effluents. They successfully combined the process of contaminated effluents treatment with simultaneous pure hydrogen production.
The technology is based on bacterial electrolytic cell, where decompose organic substances in anoxic environment emanating electrons. These electrons generate electric current used for decomposing water and recovering hydrogen on the cathode.
Winery effluents saturated with organic substances (alcohols, acids, phenols and other substances impeding biological treatment) were used for testing. To make the system able to deal with such complex blend, the researchers prepared a special germ culture. It comprised the bacteria collected from dump sites, mine drainage and municipal wastewater treatment facilities. These microorganisms were “pre-trained” to operate in difficult environment by adding organic substances and heavy metals. Also, Geobacter sulfurreducens bacteria capable of effective transmission of electrons to the electrode were added to the culture, thus increasing the electrochemical reactivity of the system.
The test lasted for over 5,000 hours. At the initial stage, microorganisms were grown in simple nutrient media to provide for their capability to form sustainable bioelectrically active film on the electrode surface. Then the winery effluents were added gradually to the system watching how it was able to cope with the real load. The results turned out very good: the degree of removing organic contaminants exceeded 55% judging by chemical oxygen demand (COD), and the average daily hydrogen yield made circa 0.7 liter per 1 liter of the plant volume. Such results were obtained after adding only 5% of real effluents, which is a sign of high sustainability of the germ culture and its ability to adapt even to complex and potentially toxic environment.
To assess the results, the scientists applied electrochemical impedance spectroscopy: this method allows for monitoring the growth of bacterial film and the charge transfer effectiveness in real-time mode. This allowed for identifying the time dynamics of the bio-film structure, where electric losses arise, as well as for monitoring the effect of the effluents’ composition on the process stability.
In future, the researchers plan to scale-up the technology for pilot and commercial plants. However, at this stage they are focused on several key areas: improving the cathode materials to decrease energy losses, exploring the possibility of adding specialized bacteria resistant to inhibitors, and using electrochemical impedance spectroscopy as a tool for operational control of the electrolysis cell in real industrial conditions.
