Efficient poultry manure management: anaerobic digestion with short hydraulic retention time to achieve high methane production

The efficient treatment or appropriate final disposal of poultry manure ( PM ) to avoid serious environmental impacts is a great challenge. In this work, the optimization of a 2-stage anaerobic digestion system ( ADS ) for PM was studied with the aim of reaching a maximal methane yield with a short hydraulic retention time ( HRT ). Three activities were performed: The first activity, ADS 1, consisted of evaluating the effect of the substrate concentration and the HRT on the process, with a constant organic loading rate ( OLR ) of 3.66 ± 0.21 gVS L −1 d −1. The second activity, ADS 2, consisted of decreasing the HRT from 9.09 to 2.74 d with a constant substrate concentration. In the third activity, ADS 3, the substrate concentration was increased from 10.09 ± 1.41 to 35.25 ± 6.20 gVS L −1 with an average HRT of 4.66 ± 0.11 d. Maximal methane yields of 0.22, 0.21, and 0.22 LCH 4 gVS −1 were reached for ADS 1, ADS 2, and ADS 3, respectively, at a low HRT (3.38 to 4.66 d) and high free ammonia concentration (between 323.05 ± 56.48 and 460.93 ± 135.40 mgN-NH 3 L −1 ). These methane yields correspond to the production of 40.36 and 42.28 cubic meters of methane per ton of PM, respectively, and a laying hen produces between 47.45 and 54.75 kg of PM per year in Chile. Finally, this is the first study of the separate and combined effects of OLR, HRT and substrate concentration on the anaerobic digestion of PM. The results demonstrate the technical feasibility of the two-stage ADS treatment of PM with a short HRT; the system tolerates variations in the total ammonia nitrogen concentration of PM throughout the year and achieves a high methane yield when the correct operational conditions are selected.