Continuous biohydrogen production by co-digestion of alkali-treated food waste and sewage sludge

Abstract

Hydrogen is a promising alternative, environmentally ``friendly`` and sustainable energy carrier. $H_2$ can be produced by dark fermentation of carbohydrate-rich substrates, giving organic fermentation end products, $H_2$ and $CO_2$. Organic wastes are regarded as a desirable feedstock because they are inexpensive, abundant and nutrient-rich. Besides, waste reduction could be achieved as well. Food waste and sewage sludge are the most abundant and problematic organic wastes in Korea while their conventional disposal options would not be acceptable in the near future. As the above mentioned wastes have different characteristics, co-digestion might be synergistic for hydrogen production owing to balanced organic and inorganic compositions. This work was, therefore, performed to investigate continuous hydrogen production from these wastes. Firstly, effects of alkaline treatment on organic waste were examined. Four initial pH values of sewage sludge, pH 11.5, 12.0, 13.0 and 13.5, were examined by addition of 60, 74.5, 120 and 312.3 meq KOH/L, respectively. At initial pH 13.0, soluble carbohydrate and soluble protein compositions reached the maximum values, 69% and 70%, respectively. As carbohydrate is the main carbon source and protein is one of the important nutrients in hydrogen production, initial pH 13.0 was considered as the optimum alkaline treatment condition for hydrogen fermentation. Also, carbohydrate and protein compositions of food waste reached 51 % and 16 %, respectively, at initial pH 13.0. Furthermore, the bacteria counts of sewage sludge and food waste decreased about 3.5-log and over 7.8-log (CFU), respectively. It meant that alkaline treatment was efficient for disinfection as well as solubilization of the organic wastes. Secondly, $H_2$ production tests were performed to investigate feasibility of hydrogen production from alkali-treated food waste and sewage sludge under various VS concentrations (1.5~5%) and mixing ratios of food waste and ...