Optimisation of anaerobic co-digestion in two-stage systems for hydrogen, methane and biofertiliser production

Abstract

This study responds to the need to optimise anaerobic digestion to achieve the integral valorisation of waste in a sustainable way, obtaining maximum yields in the production of biofuels and biofertilisers. To achieve the maximum benefits of this technology, anaerobic co-digestion with phase separation by temperature and microorganisms (TPAD) of sewage sludge and waste from the agri-food sector (poultry manure and vinasse) was tested. To this end, each phase was optimised separately by applying different hydraulic retention times (HRT) first in the thermophilic acidogenic phase and then in the mesophilic methanogenic phase, in order to find the optimum conditions in terms of hydrogen and methane yield, volatile solids (VS) removal and pathogen removal in the effluent. The results obtained show a maximum hydrogen yield of 40.41mLH2/gVS in the acidogenic phase at 5 days of HRT and a methane yield of 391.0mLCH4/gVS in the mesophilic methanogenic phase at 12 days of HRT, respectively. At the end of the process, a total removal of VS of 93 % and of pathogens of more than 96.7 % was achieved, which would allow it to be classified as class A biosolid according to USEPA. Therefore, this technology would allow solving a local environmental problem of organic waste generation, valorising it in the form of biohydrogen, biomethane and biofertiliser, thus contributing to the transfer to a circular economy model.