Browsing by Subject "Ethylendiamintetraessigsäure"

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Einsatz von Spurenelementen bei der Vergärung von nachwachsenden Rohstoffen in Biogasanlagen
(2014) Vintiloiu, Anca; Jungbluth, Thomas
The operational agricultural biogas plants in Germany are fed mainly with renewable raw materials. During substrate addition, several micro and macro elements enter the digester. These elements are essential nutrients for the methanogens. If their concentration is too low, the production of biogas can be disrupted. A large number of agricultural biogas plants use therefore commercially available trace element solutions to optimize the process and to achieve higher methane yields. When the fermentation is complete, the digestate containing these trace elements (mostly heavy metals) is spread on fields as fertilizer. The amounts added to the biogas process should be kept as low as possible in order to minimize the environmental damage. The purpose of this study was to investigate the cause of trace elements deficiency in renewable raw materials fed biogas plants. It was also tested whether the chelation of the nutrients could increase their bioavailability for microorganisms and thus lead to a reduction of the amounts needed for the stabilization of the fermentation process. The effect of the complexing agent ethylenediaminetetraacetic acid (EDTA) on the bioavailability of metal ions was tested. The sole addition of EDTA to an undersupplied substrate increased the methane yield by up to 32 %. When trace elements were also added, their amounts could be reduced by up to 75 % with no negative consequences for the fermentation process. EDTA is a persistent chelating agent and so it was further tested, whether readily biodegradable chelating agents (ethylenediaminedisuccinic acid (EDDS) and iminodisuccinic acid (IDS)) could have the same effect. During the investigation, IDS had a high statistically significant positive effect on the bioavailability of the metal ions, which exceeded the effect of EDTA. IDS represents therefore a good alternative to EDTA. The bioavailability of the metal ions in the digester was increased by the use of complexing agents, which made the reduction of the trace elements amounts needed to compensate for substrate-related deficiency symptoms possible. This reduces the pollution on the agricultural land on which the digestate is used as fertilizer.