ANAEROBIC CODDIGESTION OF RAW EFFLUENT AND FLOAT SLUDGE FROM POULTRY SLAUGHTERHOUSE: EVALUATION OF THE A/M RATIO AND THE INFLUENCE OF FLOAT SLUDGE CONTENT ON BIOGAS PRODUCTION

Abstract

Poultry slaughterhouses generate large volumes of effluents with a high content of organic matter and lipids. Among the alternatives available for treatment, anaerobic digestion provides the transformation of these effluents into biogas. The objective of this work was to evaluate the anaerobic codigestion of fresh sludge from the flotator to the raw effluent of a poultry slaughterhouse. The codigestion assays were carried out in reactors (500 mL of total volume and 300 mL of useful volume), operated in batch under mesophilic conditions (30 ± 1 °C), with an incubation time of 108 days. An experimental design of the Central Rotational Composite Design (RCCRD) was adopted, comprised of a 2² factorial with four trials at levels +1 and -1, four trials at the levels of axial points (-1.414 and +1.414) and one more triplicate at the central point (0), the response variables were: accumulated production of CH₄ (L) and yield CH4 (L CH4/g SV added),  five levels of fresh sludge addition from the flotator (V/V) (15.9, 20, 30, 40 and 43.5%) and five levels of food/microorganism ratio (A/M) (0.3, 0.5, 1.0, 1.5 and 1.7) were tested. The results of the batch tests did not indicate a significant effect for the response variables: accumulated yield of CH₄ and accumulated production of CH4. However, the R1, R10, and R7 reactors demonstrated better efficiency in the conversion of organic matter into biogas, with yields of 0.83, 0.80, and 0.71 L CH4/g SV added respectively for each reactor.