PAHs in feed coals and fly ashes from coal-fired thermal power plants in Bulgaria

The first thorough study of PAHs in feed coals and FAs from combustion in six Bulgarian TPPs was done. Since coal-derived FAs are applied to many targets, it is imperative to enhance the knowledge for their geochemical composition and environmental impact. The gap of information on PAHs in feed coals and coal-derived FAs has outlined the aim of the study: (i) to compare by geochemical proxy PAHs in feed coals and FAs generated in six Bulgarian TPPs; (ii) to track the changes in PAHs compositions with feed coal ranks and in different ESP rows; and (iii) to estimate the potential toxicity of FAs (if any). Extractable organic matter (EOM) was prepared. PAHs were isolated in aromatic fractions and quantified in mu g/kg. The total PAHs for lignite feed coal are in the range 400-530 mu g/kg and for FAs 0.30-12.60 mu g/kg: for subbituminous feed coal, they are 4000 mu g/kg, and for FAs, 1.10-32.50 mu g/kg. For bituminous feed coals, they are - 860 mu g/kg and 9305 mu g/kg, and for FAs from both TPPs, they are several times lower, from 69.4 mu g/kg to 103.3 mu g/kg, for the five ESP rows of Varna TPP and from 100.4 to 182.20 mu g/kg, for the three rows of ESPs of Russe TPP. The EOM for low rank feed coals is strongly dominated by coal biomarkers, i.e., perylene and phenyl substituted PAHs. Therefore, calculations and ratios based on PAHs compositions are done only for bituminous feed coals and their FAs. Combustion has resulted in a regular shift to lighter PAHs compared to the signature PAHs of feed coals. PAHs distributions in FAs are dominated by phenanthrene. Distribution profiles according to the number of aromatic cycles (R) in PAHs are dominated by threering (3R) PAHs > four-ring (4R) PAHs. Only in the last row of ESP from the Varna TPP is there evidence for the presence of heavier PAH, five-ring (5R) benzo[g,h,i]fluoranthene, trapped by the finest particulate matter. Relatively low PAHs concentrations determined for FAs are compared with the values for PAHs in soils according to the Bulgarian regulation.

Automated summary

The study conducted the first thorough investigation of PAHs in feed coals and FAs from combustion in six Bulgarian TPPs, aiming to compare their geochemical compositions, track changes in PAHs compositions with different feed coal ranks and ESP rows, and estimate the potential toxicity of FAs. Results show variations in PAHs concentrations between feed coals and FAs, with combustion resulting in a shift towards lighter PAHs. PAH distributions in FAs are dominated by phenanthrene, and the presence of heavier PAH, benzo[g,h,i]fluoranthene, was only found in the finest particulate matter in the last row of ESP from Varna TPP.