Fly ashes generated from coal-fired thermoelectric power plants on the Balkan Peninsula – Organic geochemical study

Abstract

Organic matter (OM) presence in fly ashes (FA) might be a serious obstacle towards their utilization or beneficial use. Though, it is imperative to enhance the knowledge of FA geochemical composition and environmental impact. Feed coals and FA from thermoelectric power plants (TPP) in Bulgaria (Maritza East 2 TPP), Greece (Megalopolis TPP and Agios Dimitrios TPP) and Serbia (TENT A, Nikola Tesla A TPP and TENT B, Nikola Tesla B TPP) were comparatively studied by geochemical proxies. Extractable organic matter, 0.45–6.10% for the feed coals and 0.013–0.025% for the FA, was subjected to extensive chromatographic separation and species in different chemical series were GC–MS identified and quantified. Changes in the biomarker assemblages triggered by combustion in the pairs feed coal/FA were picked up, series of chemical classes quantified and subsequently alterations in chemical series were expressed in rel. %.Combustion has affected the biomarkers separation mode though the signatures for FA keep some features of the parent coals. Feed coal biomarker were rich in functionalities as were composed by a broad range of series, i.e., n-alkanes, regular isoprenoids, terpenoids, hopanoids and their aromatized counterparts. Polycyclic aromatic hydrocarbons (PAH) are of especial environmental concern. After combustion, FA biomarkers pattern of distribution was simplified as only two main series remained at appreciable amounts, n-alkanes and diterpenoids. Aromatic triterpenoids were also recognizable. Combustion has altered the n-alkanes separation mode as in the distribution curves for FA samples was visualized well-expressed shift to the shorter-chain n-alkanes, nC15-nC19.There were some similarities in PAH assemblages for FA from the studied thermoelectric power plants (TPP) as the combination of fluoranthene, pyrene, benzo[a]anthracene, chrysene and benzo[k]fluoranthene was rather frequent. Also, in all samples (except Maritza East 2 TPP) there was a preponderance of the four rings (4R) PAH and considerable presence of 5R PAH, i.e., benzo[k]fluoranthene. Ranges for ΣPAH (16 USEPA) and ΣCPAH for FA were: ΣPAH (16 USEPA), 1.5–33.0 μg/kg, and ΣCPAH, 0–12.0 μg/kg. Respectively, values for FA Benzo[a]pyrene equivalent (B[a]Peq) up to 0.80 μg/kg and toxic equivalency quantities (TEQ) up to 1.22 μg/kg values were calculated. The range of 4–12 μg/kg for ƩCPAH was considerably lower than 300 μg/kg designated by the Swedish Environmental Protection Agency (Swedish EPA) for FA used in soil remediation. Enrichment ratios, ER < 1, for all TPP located on the Balkan Peninsula implied that PAH were mostly emitted into the atmosphere by the flue gases.