A Study of Underground Coal Gasification (UCG) Wastewater and Sludge

Underground coal gasification (UCG) is a non-conventional method of extracting gas from coal. The primary advantage of UCG is that it recovers gas from uneconomical or unminable coal, potentially increasing the value of the world’s coal reserves by an estimated 70%; for this reason, UCG has been implemented at sites around the world. However, the gaseous, liquid and solid waste streams which accompany UCG are the source of known mutagens and carcinogens, and potential contamination of groundwater has been identified. In the absence of any meaningful data on UCG waste, this study sought to identify the main organic and inorganic chemical and odoriferous properties of UCG wastewater and sludge from a site in Australia, and examined the roles of oxidization, biostimulation and metal sequestration in the treatment of wastewater and sludge generated by the gasification process. Findings suggest that UCG wastewater and sludge emanate a highly objectionable odour and contain significant concentrations of benzene, toluene, a range of petroleum hydrocarbons, and phenols, but relatively low levels of heavy metals and no polycyclic aromatic hydrocarbons, pesticides or polychlorinated biphenyls. Both oxidation and biostimulation destroyed organic contaminant species by >95%, and sequestration reduced inorganic contaminant species by >94%. As this represents one of the first reliable studies to investigate UCG odour, wastewater and sludge, further research is required to better understand and document the environmental and human health effects, if any, of short-term and chronic exposure to these types of wastes.