Bio-hydrogen and methane production using dark fermentation

Hydrogen is regarded as an energy source of the future. Currently hydrogen is predominantly produced by electrically driven electrolysis of water or by steam reforming. Both methods base on fossil fuels. These days the production of hydrogen by biological processes has become a matter of global interest and attention (Levin et al., 2004).

Further Author:
A. Schorn - University of Duisburg-Essen

Alongside photo-fermentation and bio-photolysis, dark-fermentation is a possible biological method to produce hydrogen. In order to fit every day energy requirements, those methods have yet to be enhanced and adapted to an industrial scale. Previous research of a two stage test set up with bio-hydrogen production as first stage, followed by a “conventional” anaerobic digestion step with a tenfold volume showed, that it is possible to combine these processes. By doing so, it is important to strictly divide both steps from each other because the methanisation stage can affect the hydrogen production negatively. This paper deals with first lab-scale test series in order to define suitable substrates for a pilot plant (volume of hydrogen and methane tank 1 m³ each). Simultaneously, effects of disturbances are observed by simulating a leakage of the reactor as well as a failure of the heating system. The continuously stirred hydrogen reactor has a volume of 4 L and is running at mesophilic conditions around 35 - 36 °C. Digested sludge from a nearby waste water treatment plant (WWTP) was used as seed sludge and pretreated by heating up to 70 °C for an hour. In order to give the microorganisms time to adapt, 2 L seed sludge are mixed with 2 L of the respective substrate solution and stirred for a period of 48 hours. Afterwards the continuous experiment was started. Polluted industrial sugar and bakery wastes have been used as substrates. Both substrates have been diluted with tap water until a concentration of 10 g volatile solids (VS)/L was reached. The reactor is running semi-continuously by feeding the substrate once an hour. Testing of sugar-solution as substrate lead to average biogas productions of 971.86 mL/(LR*d). Maximum production rates of 1,392.70 mL/(LR*d) could be obtained. Furthermore, the arithmetical mean of hydrogen-yields was 77.84 mL/g VSadded. Hydrogen content of produced biogas was varying between 36.8 % and 44 %. Experimental set up with bakery wastes showed comparable results regarding the amount of produced biogas. Peak level was at 1,448 mL/LR*d. Hydrogen contents from 30.2 to 52.3 % could be found. Hydrogen-yields alternated between 49.1 and 205.8 mL/g VSadded. Although the breadcrumbs-fed reactor ran at distinctly shorter HRT´s, sugar and breadcrumbs both lead to comparable amounts of produced biogas. This outcome can be ascribed to the fact, that bread or rather carbohydrates are not as biologically available as plain sugar. The simulation of a failure of the heating showed, that low temperatures induce inhibited biological activity whereas metabolic processes themselves remain the same. An aeration of the reactor lead to increased production rates of biogas and hydrogen yields. Both simulated disturbances do not seem to harm the process irreversibly, if adjusted promptly. The combination of the two treatment steps bio-hydrogen production and “conventional” anaerobic digestion is a feasible option for example for the treatment of mono-charges, which is otherwise ensured by cost intensive enlargement of digester volume or massive reduction of organic load rate (OLR). In the context of the pilot scale research, it has to be evaluated, if energy recovery by the combination of hydrogen- and methane-production with fuel cell is comparable to the conventional anaerobic digestion which uses combined heat and power plants (CHP) to produce electricity.



Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 8
Preis inkl. MwSt.: € 8,00
Autor: Maren Stommel
Ruth Brunstermann
Prof. Dr.-Ing. Renatus Widmann

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