This paper describes a study of the effects of hydrothermal dewatering of raw tropical peat from Pontianak, West Kalimantan-Indonesia, on the amounts of organic compounds released into and gaseous products. Hydrothermal upgrading and dewatering of the peat was carried out in a batch-type autoclave reactor at temperatures between 150 and 380 degrees C at a maximum pressure of 25.1 MPa for 30 min. It was found that the extent of decomposition of organics during hydrothermal dewatering depended on temperature increase. Wastewater from hydrothermal dewatering was found to contain organic carbon (TOC) ranging from 800 ppm at low temperatures, to 7504 ppm at high temperatures. A number of sugars and furans were detected in the wastewater at 250 degrees C, and organic acids and alcohols at all temperatures. Phenol and phenolic derivatives were observed at 250 degrees C, and significant amounts of CO(2), CO and H(2) were detected at all temperatures studied; CH(4) was detected only at 380 degrees C, but at this temperature CO(2) was no longer detected. A simplified schematic diagram of the decomposition behavior of tropical peat in the hydrothermal dewatering process is discussed with respect to the change in the concentration of organics in wastewater and gaseous products as determined by TOC, GC, GC-MS and (13)C NMR analyses of the solids produced. (C) 2010 Elsevier Ltd. All rights reserved.