Design And Operation Parameters Optimization Of SARD Bio-hydrogen Production Reactor For Food Waste Anaerobic Fermentation

Food waste quantity in Shanghai was estimated to be over 1300 tons/day, 10.8% of the Municipal Solid Wastes. It is characterized by high water content （85%） and volatile solids （VS: 80%～90%）, with potential energy via anaerobic digestion for production of methane and hydrogen, as done in this work.In this work, an innovative anaerobic fermentation reactor for hydrogen production named SARD （Semi-continuous Anaerobic Rotary Drum） was designed and operated for semi-continuous fermentation using food wastes as source material. Meanwhile, the conventional CSTR and Plug .Flow Reactors were also made and operated in parallel with the SARD. It was found that the performance of SARD was much better than CSTR in terms of hydrogen production rate and content as well as loading.Using the reactors made, the anaerobic digestion tests were done systematically. It was shown that the food wastes alone may be acidified soon and little hydrogen can be detected. Hydrogen concentration in the biogas would increased to 4～6% when the wastes was inoculated by heat-treated anaerobic sludge, depending on the heating time and temperature for the sludge. The addition of inert porous materials was proved to be effective for improving the hydrogen production. Moreover, high dosage of age refuse （>25% in weight） could considerably increase the hydrogen production amount, with an establishment of butyric acid type fermentation. The fermentation operation could normally run under the conditions of the sterilization treatment of both food waste and sewage sludge （160 ℃, 1.5 h）. A hydrogen production rate of 187.46 mL/g VS was obtained under conditions of 36 ℃, 50% inoculation rate of age refuse, water content of 90%, and food wastes to sludge ratio of 100:30 （dry weight）. The process of hydrogen production was well fitted by Germpertz equation, from which the potential and special rate of hydrogen production from food wastes were evaluated at 193.85 mL/gVS and 94.35 mL/（h·gVS） respectively.The scale-up tests for SARD reactors were conducted. It was indicated that the feed-in loading should be increased gradually to avoid system breakdown, and food wastes alone were not fit for hydrogen fermentation due to its high content of organic matters. When the feed-in loading reached 20%, the hydrogen concentration dropped below 20%, which may be contributed to the rapid growth of hydrogen consumptation bacteria, evolution of CO₂, reflux and other negative factors.A hydrogen concentration and production capacity of 45% and 100～120 mLH₂/gVS can be obtained at the optimum operation parameters for SARD at length/diameter 8:1, refllux ratio 0.5, rpm 20, mixing time 2 rain, stirring interval 4 h, angle 1.5°, in which the reflux ratio was the main influencing factors, this condition. The operation can continuously perform for 680 h （28 d）, and 30 m³hydrogen/ton wet food wastes can be obtained.