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Biomethane potential tests

To test the effect of thermo-chemical pretreatment of lignocellulose rich substrates, not treated and pretreated substrates were anaerobically digested via biomethane potential tests. Generally, the degradation rate of methane production could be increased by thermo-chemical pretreatment of lignocellulose rich substrates. However, the total methane yield was not generally increased for every sort of pretreated substrate. The increased degradation rate is advantageous because it means that the hydraulic retention time and thus the reactor size could be decreased if thermo-chemical pretreatment of lignocellulose rich substrates is performed.

 

Desulphurization

The aim was to optimize microbiological desulphurization of H2S rich biogas with respect to fast and efficient sulphuric acid production. For that, a continuous desulphurization unit for microbial H2S conversion was constructed at lab-scale. Potent sulphur oxidizing bacteria were immobilized in this column to produce sulphuric acid in sufficient concentration for substrate pre-treatment.
Lab scale experiments proved the suitability and stable operation of the designed desulphurization column for H2S conversion into sulphuric acid. Highest sulphate production rates (acid determined as sulphate) were achieved at 100% H2S removal with a total elimination capacity (EC) ranging between 200-300 g m-3 h-1.
 

The constructed column for microbial desulphurization is capable of both, stable H2S removal at 100% removal efficiency and subsequent conversion to sulphuric acid in sufficient concentration for lignocellulose pre-treatment prior to anaerobic digestion.

 

Continuous fermentations at pilot-scale

After the completion of the pilot-plant, two runs of continuous fermentations were carried out. During the fermentation, parameters of the fermentation broth as well as gas production and composition were monitored. The results from the methanogenic stage were promising as the observed specific methane yield covered 80% of the results from the bio-methane potential tests.