Study on the Utilization of Liquid Waste from Local Food Industry for Hydrogen Production by Using Photosynthetic Bacteria Rhodobium marinum

Abstract

New, clean and renewable energy systems are required to encounter environmental problems caused by the use of fossil energy sources. Hydrogen is energy carrier that fulfills requirement of clean and environmental friendly energy because hydrogen does not produce greenhouse gases in its combustion. Photosynthetic bacteria are one among other bacteria that can produce hydrogen through photo fermentation process. Liquid waste can be utilized as substrate to produce hydrogen by photosynthetic bacteria. In this study, liquid wastes from local food industries are utilized as organic sources for hydrogen production process because of economical and environmental reasons. Photosynthetic bacteria, Rhodobium marinum, were used as the agent for hydrogen production. Milk, soya sauce and tofu liquid wastes were chosen as organic sources. These liquid wastes were treated by centrifugation, neutralization and sterilization. The wastes also have been characterized and it contains sugar, organic acid and protein. Milk liquid waste directly can produce hydrogen about 141±24 ml after been treated, meanwhile soya sauce liquid waste did not produce hydrogen and had to be diluted. Tofu liquid waste also did not produce hydrogen and could not be continued for optimization because of its small content of nutrients. Milk and soya sauce liquid wastes were examined with dilution (1-80 g/l), addition of iron (0-500 μmol/l for milk liquid waste and 0-160 μmol/l for soya sauce), molybdenum (0-12 μmol/l for milk liquid waste and 0-160 μmol/l for soya sauce) and sodium bicarbonate (0-6 g/l) for optimization purposes. The dilution of milk liquid waste that gives 7.58 g/l total sugar concentration had the highest efficiency with 3.22% mol hydrogen/mol hydrogen theoretical and 10.9 g/l for soya sauce with 6.88% mol hydrogen/mol hydrogen theoretical. From these experiments, the addition of iron, molybdenum and sodium bicarbonate does not affect hydrogen production from milk and soya sauce liquid wastes. For kinetics parameters, milk and soya sauce liquid waste which were treated by pretreatment and without addition of iron, molybdenum, sodium bicarbonate, yeast extract and trace element in SL-6 solution were used as hydrogen production medium with 900 ml working volume. From the experiments, the maximum specific growth for R. marinum in milk liquid waste was obtained to be 0.137 hours-1; Yx/s value was 0.45 g biomass/g substrate, Yp/s value was 0.017 g hydrogen/g substrate and Yp/x value was 0.031 g hydrogen/g biomass. The maximum specific growth for R. marinum in soya sauce liquid waste was obtained to be 0.245 hours-1; Yx/s value was 0.475 g biomass/g substrate, Yp/s value was 0.041 g hydrogen/g substrate and Yp/x value was 0.086 g hydrogen/g biomass.