Co-composting of poultry manure with low quantities of carbon-rich materials.

To study the feasibility of co-composting poultry manure with low quantities of high-value, carbon-rich materials experiments to characterize three pilot-scale piles were carried out. The piles comprised poultry manure (pile 1), poultry manure and straw (pile 2) and poultry manure and sawdust (pile 3), using wood chips as bulking agent. Pile 1 presented the highest losses of organic matter and nitrogen contents (> or = 92.9% and 92.0%, respectively). Although a thermophilic phase (temperature > 40 degrees C) was not verified for this pile, the final compost was stable (class IV) and free of pathogen indicator micro-organisms but it was the most phytotoxic, and presented a humic and fulvic acids ratio (HA/FA) that was less than 1. In contrast, piles 2 and 3 sustained thermophilic phases and produced stable (class V) and mature (HA/FA > 1) composts. Pile 2 showed the lowest loss in nitrogen content (88.9%) and produced the final compost with the highest C/N ratio (14.7) and the lowest value of electrical conductivity (3.9 mS cm(-1)). This study showed that it is possible to reduce the costs of poultry manure composting, namely the costs associated with the use of carbon-rich materials, given that the final co-composts presented parameters within the range of those recommended by the Second Draft Proposal for compost quality.