Final treatments for anaerobically digested piggery slurry effluents

Different final treatments for light fractions from anaerobically digested pig wastes (1 mm) and coarse fractions (> 2 mm or obtained by flocculation) have been carried out. Coarse fractions may be treated in a batch reactor for a long residence time (60 days), at 35°C, in order to produce a significant volume of methane-rich biogas and a semisolid residue suitable to be used as a fertilizer. Final processings for light fractions, flocculation (by means of inorganic additives and organic polymers), aerobic digestion and chemical oxidation were investigated with the aim of improving chemical oxygen demand (COD) elimination. Results of an integral process—consisting of anaerobic digestion of both light fractions in a continuous reactor, and coarse fractions in a batch reactor, followed by a final effluent treatment—are also included, with the double aim of biogas production and COD reduction.