Anaerobic Co-digestion in a Pilot-Scale Periodic Anaerobic Baffled Reactor (PABR) and Composting of Animal By-Products and Whey

摘要

The combination of anaerobic digestion and composting is examined as an integrated valorization process of the livestock waste generated in rural areas. Both biogas and high quality compost may be produced by such a combined process. Six different kinds of waste (pig manure, cow manure, cattle manure, poultry manure, sheep manure and whey) were mixed considering the annual waste production of Metsovo region, Greece, in a representative way. The feed was subjected to a solids/liquid separation step. The bioreactor was operated in different phases with different organic loadings of the liquid fraction of the waste. During phase #1, the Periodic Anaerobic Baffled Reactor (PABR) was fed with a hydraulic retention time (HRT) of 10.65 days, (an organic loading rate of 0.83 g-CODLreactor-1 day(-1)) and the biogas production rate was 0.2 L-biogas L-reactor(-1) day(-1). During phase #2, the organic loading rate was increased to 1.9 g-COD L-reactor(-1) day(-1). The biogas production rate was 0.41 L-biogas L-reactor(-1) day(-1). During phase #3, the organic loading rate was increased to 2.69 g-COD L-reactor(-1) day(-1) by decreasing the HRT to 6 days, resulting in the kinetic limitation of the process. The biogas production rate increased to 0.68 L-biogas L-reactor(-1) day(-1) with an average methane composition of 65%. The experimental results obtained were used as a basis for the development of an ADM1 model (Batstone et al. in Anaerobic digestion model no. 1 (ADM1). IWA Task Group for Mathematical Modelling of Anaerobic Digestion Processes Report no 1, vol 1(1), 2002) that was able to adequately simulate the operation of the bioreactor. The solid fraction of the pretreatment step was mixed with sawdust and fed to a closed-vessel composter. The highest temperature (56.2 degrees C) was reached in 2 days. The germination index (GI) of the compost produced was 77.8%, meaning that it was free of phytotoxic substances.