Co-fermentation of tannery sludge and sunflower seed molasses boosted by Saccharomyces cerevisiae bioaugmentation

Abstract

The tannery industry is a well-developed sector that plays an important role for the global economy, and it has been heavily industrialized over the years in many countries. The attention and the research for a more sustainable development have shown its heavy environmental impact related to the high amount of chemicals and the important consumption of water employed in the operations performed to obtain the final product. Consequently, this sector generates a large amount of sludge which is laden with toxic chemicals such as chromium, and organic compounds. Due its characteristics, this sludge can only be disposed off in landfills according to the Italian legislation (D. Lgs. 04/06). Recent studies have proved that tannery sludge can be valorised in different ways like chrome recovery, biofuel generation, compost or vermicompost, and anaerobic digestion. Since anaerobic fermentation for the production of short chain fatty acids (SCFAs) has been proven effective, the main acid produced is acetic acid which has a lower economic value compared to other SCFAs with a longer carbon chain. Thus, the process of chain elongation can be employed to obtain more valuable acids, however it is usually performed by means of the external addition of an electron donor, such as ethanol. This research focuses on an alternative way of achieving chain elongation by investigating the effect of co-fermentation of tannery sludge and a sugar source on chain elongation under different conditions in two set tests. This study involved the use of two different strains (strain1 and strain2) of Saccharomyces cerevisiae as inoculum and white sugar or sunflower seed molasses as co-substrate. The bottles with the mixture were settled in mesophilic conditions.