Optimization of the anaerobic co-digestion of pasteurized slaughterhouse waste, pig slurry and glycerine.

The feasibility of co-digestion of blends of two different animal by-products (pig manure and pasteurized slaughterhouse waste) and recovered glycerine was studied in mesophilic conditions. Experiments were performed in a lab-scale CSTR along 490days, with a hydraulic retention time of 21-33days and with a step-wise increased organic loading rate, by adding and/or changing the wastes ratio, from 0.8 to 3.2kg _COD m ^-3 d ^-1 . The best methane production rate (0.64Nm ³ _CH4 m ^-3 d ^-1 ) represented an increment of 2.9-fold the initial one (0.22Nm ³ _CH4 m ^-3 d ^-1 with pig manure solely). It was attained with a ternary mixture composed, in terms of inlet volatile solids, by 35% pig slurry, 47% pasteurized slaughterhouse waste and 18% glycerine. This blend was obtained through a stepwise C/N adjustment: this strategy led to a more balanced biodegradation due to unstressed bacterial populations through the performance, showed by the VFA-related indicators. Besides this, an improved methane yield (+153%) and an organic matter removal efficiency (+83%), regarding the digestion of solely pig slurry, were attained when the C/N ratio was adjusted to 10.3.
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