Produzione di H2 e CH4 da frazioni biodegradabili di rifiuti urbani e da siero lattiero-caseario

Synthetic OFMSW was produced in laboratory, in order to make easier the comparison between the results of different tests, according to the following recipe: 8% of meat, 72% of fruit and vegetables, 8% of bread and 12% of cooked pasta (on a wet weight basis). Batch dark fermentation tests using untreated activated sludge as source of inoculum (T= 39à,°C; pH = 6.5) were performed at four F/M ratios (4; 7; 12 and 18) in order to assess the optimal one. The optimal F/M ratio resulted to be 7, corresponding to the maximum H2 yield of 89.9 Nl H2/ kg VS. Then, the effluent of the first stage (operated with the optimal F/M) was fed, mixed with methanogenic inoculum (F/M ratio = 0.5), to the second stage reactor to investigate methane production. The attained H2 and CH4 production was compared to the CH4 production achieved with a conventional single-stage batch reactor. The results confirm an higher CH4 yield for the second stage, 354 Nl CH4/kg VS versus 271 Nl CH4/kg VS for the single-stage. After a detailed analysis of the informations obtained from the batch tests, a double stage system was operated under semi-continuous conditions in order to better approximate the full scale operation. In the first semi-continuous stage, (T = 39à,°C; HRT = 2 days; pH = 6.5; F/M = 18), the average yield was 31,8 Nl H2/kg VS while in the second one a stable methane production of 432 Nl CH4/kg VS was obtained at HRT = 25 days (T = 39à,°C; pH not set). Finally, the solid phase of the digestate coming out form the double stage operated under semi-continuous conditions was composted after dewatering and mixing with a bulking agent. The final product was analysed for the main compost p