Is iron acting as nutrient for the methanogens and methane production or is it being used as a method of reducing the build up of hydrogen sulphide, which inhibits microbial activity and methane production? 

I want to use Magnetite Fe3O4 nanoparticels (particle size 10-20nm) as a nutrient to enhance methane production. My question is that whether i add nanoparticles to the digester at the start of the anaerobic digestion process or during the process? If during the process, than after how many days? Remember that the retention time for the anaerobic digestion process is 45 days. I will use rice straw as substrate and cow dung as an inoculum (2:1).

The anaerobic digestion reactions are complex biological reactions...Fe3O4 nanoparticles are added as a nutrient to increase the efficiency of bacteria so that they can biodegrade the substrate more efficiently and thus increase the production of methane.. The first stage of anaerobic digestion is hydrolysis in which cellulose and other complex sugars are converted into simple sugars. The next stage is Acidogenesis in which the sugars are converted into acetic acid acid, hydrogen and carbondioxide. The third step is Methanogenesis in which acetice acid is converted into methane.. All these conversions are carried out by different bacteria and involve complex biological reactions..

Mr. Khalid,

I know that some oligo-elements (mainly Nickel but also Iron salts or oxides) are able to rise the efficiency of methanogenesis. More exactly they act as co-enzymes in biochemical processes and facilitate the methabolic activity of methanogens. For this scope and also to not disturb the biochemical balance within the digester, such salts should be added at start of the AD, together with the biomass feedstock, dilution water and other chemicals (for example alkaline products to adjust the acidity).

Thanks Carmen for your valuable answer

Dear Junaid,

Please read these papers

http://www.sciencedirect.com/science/article/pii/S0960148115304067

Article Influence of zero valent iron nanoparticles and magnetic iro...

Thanks Dear Asad Rajput