Phytotoxic evaluation of liquid digestates obtained from anaerobic co-digestion of agricultural and livestock waste

Abstract

The improper disposal of organic wastes is an environmental problem. An alternative to this problems is to use the combined anaerobic digestion (co-AD), in which organic matter is degraded by microorganisms to produce biogas and digestate, which can be used as fertilizer. Digestate comprises a liquid fraction (biol) and a solid one. In this work the phytotoxicity of bioles obtained from different conditions of co-AD was evaluated. Four batch type biodigesters tratments and a control were prepared, all at 70% capacity, 10% solids dry basis, retention time of 60 days and mesophilic temperature conditions. The treatments consisted in 80% residue of vegetables and 20% pig manure, a group of digesters was adjusted to initial pH 6 and another initial pH 8, and with or without adjusting the Carbon:Nitrogen ratio to 20:1. PH was monitored during the process. Phytotoxicity test was done through germination index (GI). GI was calculated to the bioles of weeks 3, 6 and 8 of the process of co-DA. Six bioles obtained in different weeks were not phytotoxic, the bioles obtained from co-DA where the initial pH was adjusted to 8 were growth promoters in week 6; however, the control obtained higher GI than the treatments.