Constructed wetland as a green remediation technology for the treatment of wastewater from underground coal gasification process.

The wastewater from underground coal gasification (UCG) process has extremely complex composition and high concentrations of toxic and refractory compounds including phenolics, aliphatic and aromatic hydrocarbons, ammonia, cyanides, hazardous metals and metalloids. So, the development of biological processes for treating UCG wastewater poses a serious challenge in the sustainable coal industry. The aim of the study was to develop an innovative and efficient wetland construction technology suitable for a treatment of UCG wastewater using available and low-cost media. During the bioremediation process the toxicity of the raw wastewater decreased significantly between 74%-99%. The toxicity units (TU) ranged from values corresponding to very high acute toxic for raw wastewater to non-toxic for effluents from wetland columns after 60 days of the experiment. The toxicity results correlated with the decrease of some organic and inorganic compounds such as phenols, aromatic hydrocarbons, cyanides, metals and ammonia observed during the bioremediation process. The removal percentage of organic compounds like BTEX, PAHs and phenol was around 99% just after 14 days of treatment. A similar removal rate was indicated for cyanide and metals (Zn, Cr, Cd and Pb). Concluded, in order to effectively assess remediation technologies, it is desirable to consider combination of physicochemical parameters with ecotoxicity measurements. The present findings show that wetland remediation technology can be used to clean-up the heavily contaminated waters from the UCG process. Wetland technology as a nature-based solution has the potential to turn coal gasification wastewater into usable recycled water. It is economically and environmentally alternative treatment method.

Distribution characteristics and migration pathways of metals during hydrothermal liquefaction of municipal sewage sludge in the presence of various catalysts.

A series of hydrothermal liquefaction (HTL) experiments with two different samples of municipal sewage sludge (MSS) were conducted at 350 °C for 30 min residence time in a high pressure batch reactor. The main aim of the study was to explore the distribution and migration pathways of a broad range of metals and metalloids in the HTL products (bio-oil, char and aqueous phase) obtained in the presence of various homogeneous and heterogeneous catalysts (Na2CO3, Li2CO3, K2CO3, Ba(OH)2, Fe2O3, CeO2, NiMo/MoO3, MoS2, Ni/NiO, SnO2, FeS). The elements under study included 16 environmentally significant metals and metalloids (As, B, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, Se, Sn, Zn and Hg). The study showed that the quantitative migration of the tested metals and metalloids to the particular HTL products, relative to their initial content in the raw sludge, is different for the individual elements. Most metals exhibited a particularly strong affinity to the solid fraction (biochar). In the obtained HTL bio-oils, all tested elements were identified, except of Cd. It was also found that B and As have high affinity to the aqueous phase. A direct effect of catalysts on the contents of some elements in the products was also proved by the study, e.g. increased concentration of Cr in the biochar when Fe2O3 was used as a process catalyst. Due to the wide scope of the tested elements and broad range of catalyst used, the results obtained represent a unique and comprehensive set of environmental data compared to similar HTL studies previously conducted for MSS.

In situ sorption phenomena can mitigate potential negative environmental effects of underground coal gasification (UCG) - an experimental study of phenol removal on UCG-derived residues in the aspect of contaminant retardation.

The aim of the study was to investigate the sorption interactions between phenol and materials obtained from four different underground coal gasification (UCG) ex-situ simulations. These interactions are significant in terms of the impact of the UCG on the groundwater environment. Sorption parameters were determined for two sample types: raw coal mined from the coal-bed and then subjected to the gasification process; and char residue acquired from the cavity formed as a result of the UCG processes. Laboratory-scale tests were carried out using deionized water and aqueous solutions with increasing concentrations of phenol (from 50 mg/dm3 to 2000 mg/dm3) at 298 K. On the assumption of physical interactions (non-specific physisorption) and due to a nonlinear mass distribution of adsorbed substances as a function of equilibrium concentration, the Freundlich isotherm model was applied to describe adsorption phenomena. The isotherms have good fitting (R2 from 0.5716 to 0.9811). Relatively high percentage phenol removal efficiency was observed for all tested chars (from 17.0% to 99.8% for the 1.0-2.5 mm fraction and from 6.9% to 99.6% for the 10.0-12.5 mm fraction). Additionally, the sorption characteristics was used to evaluate the retardation coefficients. The largest delay in the organic pollutant migration in the environment around a UCG reactor occurs for phenol transport in the layer of the post-process char from 'Wesola' after 40 bar pressure experiment.