Abstract
Thermophilic anaerobic digestion is a suitable technology to treat agricultural waste because of its higher biogas production,
hygienisation effect and solids removal efficiency. Although these benefits, poor effluent quality and instability are encountered
in some cases. The anaerobic co-digestion of winery waste and waste activated sludge at 55°C, operating at 23 days HRT and
with an organic loading rate of 3.2 kg COD/m3d, was characterized by accumulation of volatile fatty acids, pH fall and reduction
of biogas production, while mesophilic process was steady at long term. The study evaluated the effect of trace elements (iron,
cobalt and nickel) augmentation in the thermophilic reactor at different concentration of micro-nutrients. The addition improved
the process stability: pH became constant and average volatile fatty acids concentration was below 1,000 mg COD/L. The biogas
production increased from 0.38 to 0.45 m3/kg COD, corresponding to 90% of COD removal, while mesophilic reactor removed
the 78% of total COD. Digestate had interesting characteristics as fertilizer in fact the higher solids removal (28%) allowed to
concentrate the phosphorus in the particulate fraction and nitrogen was transformed into more available form for plants growth.