The underground coal gasification (UCG) process, a method of extracting energy from coal without traditional mining, holds significant promise for China’s energy transition. According to research led by Lin Xin from the College of Safety and Environmental Engineering at Shandong University of Science and Technology, the technology could play a key role in producing hydrogen-rich gas while enabling CO₂ storage—a critical step toward the country’s “dual carbon” goals of peaking emissions by 2030 and achieving carbon neutrality by 2060.
Yet, as the study reveals, UCG’s environmental risks, particularly groundwater contamination, remain a major hurdle. Lin and his team analyzed gas washing wastewater from both laboratory pyrolysis experiments and real-world UCG sites, uncovering a complex mix of organic pollutants—aliphatic hydrocarbons, phenols, and benzene derivatives—that migrate through high-temperature coal gas and condense into water. Phenols, in particular, dominated the wastewater, accounting for over 37.5% of organic content.
The findings are stark: the chemical oxygen demand (COD) of water pumped from an underground UCG cavity reached 413 mg/L, exceeding discharge standards for industries like coking. As temperatures rose, so did the concentration of water-soluble organic matter, with total organic carbon (TOC) and COD levels climbing in tandem. “The relationship between temperature and pollution is clear,” Lin noted. “Higher pyrolysis and gasification temperatures generate more organic byproducts, intensifying the risk to groundwater.”
By combining TOC and COD into a single organic pollution index through factor analysis, the study provides a practical tool for monitoring UCG’s environmental impact. The research suggests that as UCG scales up, stricter process controls will be essential to prevent contamination—a challenge that could shape the technology’s commercial viability.
Published in *Meitan xuebao* (Journal of the China Coal Society), this work offers a critical framework for policymakers and industry leaders navigating the trade-offs between energy extraction and environmental protection. For an energy sector under pressure to decarbonize, the stakes couldn’t be higher.