Proceedings

The influence of micro dosage of calcium nitrate on anaerobic digestion

Franke, W.1 , Doppelbauer, G.2 , Etti, M.2 , Reid, A. 3 , Stoeck, T 4.

  1. Yara Industrial ASA, Norway
  2. Yara Industrial GmbH, Germany
  3. Yara, UK
  4. Technische Universitat Kaiserlaurtern ,Germany
(free)

Introduction

 

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

ID Electrical

power

Feed substrate Biogas production Target / Achievement
kW m3/d
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
4 1,200 Bio-waste 40,000 more biogas
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

 

Microbiological analysis

 

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.

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