Franke, W.1 , Doppelbauer, G.2 , Etti, M.2 , Reid, A. 3 , Stoeck, T 4.
Anaerobic digestion (AD) in biogas reactors is traditionally performed in a strictly anaerobic environment where electron acceptors like oxygen or nitrate should not be introduced into the reactor. But is that so? Literature indicates that adding moderate amounts of an electron acceptor to an AD system can in fact increase the gas yield as well as reduce hydrogen sulphide (H2S) formation. This study summarizes results from full scale tests where nitrate was added to AD systems, confirming those indications.
Full scale implementation
The process of micro dosage of calcium nitrate solution has been established in 10 full-scale biogas plants in Germany. The intention was to demonstrate that the technology can be up scaled and different results can be reached –depending on the needs of a plant. The dosage was applied in controlled manner with substrate feed as a proxy for the metabolic activity. The main outcome of the field tests is shown in Table 1.
Table 1: Main outcome of field tests, showing the effect of calcium nitrate solution
|Feed substrate||Biogas production||Target / Achievement|
|1||700||Corn silage, liquid manure (div.)||10,000||lower substrate demand, H2S reduction|
|2||600||Corn / grass silage, manure (div.)||6,720||more biogas|
|3||2,000||Mainly corn silage, manure (div.)||25,000||more biogas, Less substrate demand|
|5||290||Corn silage, manure||3,500||H2S reduction, more biogas|
|6||750||Grass and corn silage, manure||6,000||more biogas|
|7||150||Mainly cattle manure, corn silage||3,000||H2S reduction, more biogas|
|8||360||Mainly cattle manure, corn silage||5,500||H2S reduction, more biogas|
|9||250||Mainly cattle manure, corn silage||4,000||H2S reduction, more biogas|
|10||250||Pig / cattle manure, corn silage||3,500||H2S reduction, more biogas|
Samples originating from several full-scale biogas reactors were investigated using the analyses of taxonomic marker genes (eubacteria / archaea) obtained by Polymerase Chain Reaction (PCR) and massive amplicon sequencing (illumina). Bacterial abundance was counted with DAPI / epifluorescence microscopy.