NOVELTY - A process for the production of biogas from biodegradable material involves: a) adding the biodegradable material to the reactor; b) inoculating the microorganisms; c) adding a colloidal solution of surface-modified iron oxide nanoparticles to the reactor; d) providing anaerobic conditions; e) carrying out the anaerobic digestion; and f) collecting the biogas, where the steps (a), (b) and (c) can be carried out in any order.    USE - For the production of biogas from biodegradable material (claimed), where the biogas is used as fuels for natural gas vehicles. The biodegradable material is sludge from wastewater treatment plant, industrial residues, urban solid residues, animal by-products or agricultural waste.    ADVANTAGE - The biogas provides a sustainable alternative source of energy and hence can be used as a low cost fuel; and provides a renewable substitute for natural gas and hence can be used to fuel natural gas vehicles helping to replace fossil fuels. The method exhibits improved production efficiency. The use of nanoparticles in the process for the production of biogas from biodegradable material via anaerobic digestion results in increase of biogas production. The process is advantageous since an increase in the efficiency results in a more cost-efficient process. The use of industrial scale anaerobic digesters known in the art as a waste treatment technology had limited use mainly due to high capital costs and low process efficiencies. The nanoparticles of iron oxide dissolved in the media allow the presence of iron cations in the media. The nanoparticles ensure a homogeneous distribution of the iron ions in the solution. The nanoparticles can be used to maintain a sustained supply of iron ions to the reactor. The concentration of the nanoparticles is sustained at a determined concentration for a longer time avoiding the high concentrations corresponding to the inoculation and avoiding the rapid decrease of the concentration.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for use of iron oxide nanoparticles capable of supplying iron ions to the media for biogas production in anaerobic conditions and in the presence of iron ions in the media.