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Abstract

The production of broiler meat has increased significantly in the last decades in Germany and 3 worldwide, and is projected to increase further in the future. As the number of animals raised 4 increases, so too does the amount of manure produced. The identification of manure treatment options 5 that cause low greenhouse gas emissions becomes ever more important. This study compares four 6 treatment options for broiler manure followed by field spreading: storage before distribution,7 composting, anaerobic digestion in a biogas plant and production of biochar. For these options 8 potential direct and indirect greenhouse gas emissions were assessed for the situation in Germany. 9 Previous analyses have shown that greenhouse gas balances of manure management are often strongly 10 influenced by a small number of processes. Therefore, in this study major processes were represented 11 with several variants and the sensitivity of model results to different management decisions and 12 uncertain parameters was assessed. In doing so, correlations between processes were considered, in 13 which higher emissions earlier on in the process chain reduce emissions later. The results show that 14 biogas production from broiler manure leads to the lowest greenhouse gas emissions in most of the 15 analysed cases, mainly due to the emission savings related to the substitution of mineral fertilizers and 16 the production of electricity. Pyrolysis of the manure and subsequent field spreading as a soil 17 amendment can lead to similarly low emissions due to the long residence time of the biochar, and may 18 even be the better option than poorly managed biogas production. Composting is the treatment option 19 resulting in highest emissions of greenhouse gases, due to high ammonia volatilization, and is likely 20 worse than untreated storage in this respect. These results are relatively insensitive to the length of 21 transport required for field spreading, but high uncertainties are associated with the use of emission 22 factors.