AMMONOX: Ammonia for enhancing biogas yield and reducing NOx. Optimisation of Aqueous Ammonia Treatment

Laboratory experiments have shown that Aqueous Ammonia Soaking (AAS) is a very promising treatment for increasing the methane yield of the solid fraction of manure (fibers). AMMONOX is a new concept based on the sustainable use of ammonia for enhancing biogas production at biogas plants digesting manure. The proposed process is based on an optimized AAS treatment of manure fibers in combination with an efficient ammonia recovery step. The enhancement of biogas production is achieved by enriching manure with AAS-treated fibers or other lignocellulosic residues while the ammonia recovered can be used for fulfilling the needs of the treatment. Furthermore, excess of ammonia could be produced when ammonia is recovered from both the treated fibers and the digester effluent, which could be used for the reduction of NOx when the biogas produced is used for electricity generation by gas engines.
In this study, the importance of different factors affecting the performance of AAS of digested manure fibers was investigated in order to conclude on the variables to optimize. Principal Component Analysis of the experimental data obtained so far was used for a preliminary analysis of effects. The temperature and the ammonia concentration during AAS were pointed out as the most influencing variables in terms of methane yield under the conditions tested. Further experiments should be conducted in order to investigate the effect of AAS duration at lower values than the ones tested (lower than 24 hours) and for assessing the importance of the solids to liquid ratio in the treatment mixture.