Gli scarti organici per la produzione di energia tramite digestione anaerobica: una sfida multidisciplinare

7 febbraio 2018, ore 11.30, presso Sede IRSA Montelibretti (Roma) - Sala Riunioni primo piano
ing. Pamela Pagliaccia
Gli scarti organici per la produzione di energia tramite digestione anaerobica: una sfida multidisciplinare

In a society that witnesses an ever-increasing generation of organic solid wastes (OSW) and an urgent need for a stable source of renewable energy, the opportunity of integrating OSW treatment and bioenergy sectors in a unique process (anaerobic digestion) seems a captivating option. However the recovery of biomethane (or biohydrogen) in the shortest time with a stable operation is challenging. To maximise the performance and enhance the anaerobic digestion (AD) process, both thermal pre-treatment and thermophilic regimen have been investigated. BMP assays were conducted on a diverse array of complex materials, including kitchen food waste (KFW), fruit and vegetable scraps (FVS), organic fraction of municipal solid waste (OFMSW), olive husks (OH), paunch, and food waste with constant composition (FWCC) to evaluate how physical and chemical characteristics affect biomethane potential and overall biodegradability, with or without thermal pre-treatment, in mesophilic and thermophilic conditions. Characterization was accomplished basing on traditional physico-chemical parameters and macromolecular compounds. Moreover, apart from the characterization before and after the pre-treatment and at the beginning and the end of the digestion, importance was also given to the evolution of the substrate features during the process, deepening the knowledge on what happens during AD. Aim of the study was also to evaluate performance and stability of food waste anaerobic digestion over long-term periods, scaling up from BMPs to continuously stirred anaerobic digesters operated at semi-continuous conditions. This allows dealing with new system variables, like microbial community and inoculum quality used for the start-up of an anaerobic reactor, which are critical factors for successful biogas production and better identify potential problems and malfunctioning in full-scale application. Every step highlighted strengths and weaknesses and allowed to define an ample scenario on the enhancement of AD of complex organic substrates into energy. First of all the study proved that an accurate characterization in terms of macromolecular compounds analysis along with the usual physico-chemical parameters analysis was a very helpful tool in order to deepen the understanding of the whole process. The multiple and diverse batch tests permitted to understand and distinguish among effects due to substrate change, pre-treatment, substrate/inoculum (S/I) ratio and temperature. It was found out that H2 production (promoted by high carbohydrates content) was the most sensible variable to parameters modification, particularly pre-treatment and S/I ratio. There was a consequent VFA accumulation together with the H2 production phase, which could lead to inhibition and process failure at high organic load (temperature sensitive phenomenon). Moreover, batch tests were able to predict the extent of prompt fermentability and biodegradability, as acidification phenomena, too. Intense acidification phase was confirmed in semi-continuous trials: VFA build-up was observed as the duration of operation continued indicating long-term instability; which was found to be a delicate process and not easy to deal with in modelling analysis. The significant impact of the feedstock characteristics on system stability and methane conversion rates was limited by changing feeding regimen.