Abstract

A biphasic anaerobic process for fruit and vegetable wastes (FVW) with pig manure as co substrate in the acidogenic step and lignocellulosic packing in the methanogenic step was tested. A process starting up with three days of a thermophilic acidogenic digestion, followed by a twelve days methanogenic mesophilic digestion packed with wood chips, was implemented, and assessed in terms of efficiency in methane generation and content in biogas. Additionally, alkaline extraction of humic compounds from the residual waste sludge was characterized as liquid humus fertilizer. Average results for 15 days of total hydraulic retention time (HRT), showed a production of 270.3 ml of methane per gram of volatile solids (VS) with 63.5 % of them removed, this is 14 % higher than without lignocellulosic packing, while biogas content of 65.9 % of methane, 9 % higher also. On the other hand, the liquid humus obtained qualified as carbonated organic fertilizer. Even though the conversion efficiency of volatile solids achieved was moderate, the combination of the hydraulic retention time (HRT) and the yield in methane generation, permits a reduction in the size of digestion reactors and the possibility to obtain a high quality liquid biofertilizer