Assessment of the stability of livestock farm wastes treated by anaerobic digestion

The degree of stability attained by livestock farm wastes (cattle and poultry manure) through anaerobic digestion was studied by means of thermal analysis and various stability assays, such as carbon mineralization, degradability bio-assays and phytotoxicity. Results from these tests coincided in assigning a greater degree of stabilization to the poultry digestate. Thermal profiles obtained from fresh and stabilized samples revealed that digestion leads to a reduction in the amount of materials that are oxidized at low temperatures and an increase in the residual mass at the end of thermal oxidation. From thermal analysis it was found that peaks in the differential thermogravimetry (DTG) profile could be associated with the labile and resistant fractions obtained from the mineralization assay. The results of the respirometric test performed on stabilized samples are in accordance to the intensities of the peaks registered at low temperature in the DTG profiles. The phytotoxicity test indicated no toxic effects from the digestates.