The objective of this study was to evaluate the promotion effect of ammonia on the biodegradation of polylactide (PLA) under hyperthermophilic (80 degrees C) and thermophilic (55 degrees C) anaerobic condition. The results showed that PLA was transformed to lactic acid under hyperthermophilic conditions, but that the transformation ratio was negligible under thermophilic conditions. The hydrolysis process can be markedly increased with ammonia addition and microorganism activity. The maximum transformation ratios of the two kinds of PLA used in this study were 65.2% and 51.8%, respectively, with ammonia addition of 4 g N/L over 3 days treatment of anaerobic sludge. After the hyperthermophilic pretreatment, the hydrolysis products were converted to methane by methanogens under the thermophilic and anaerobic conditions. The final methane conversion ratios of the two kinds of PLA after 22 clays treatment were 81.8% and 77.0%, respectively. (C) 2011 Elsevier Ltd. All rights reserved.