Preservation of geochemical markers during co-combustion of hard coal and various domestic waste materials

Combustion of domestic waste for heating purposes in non-adapted furnaces is a common environmental problem all over the world since it leads to significant emission of harmful substances to the atmosphere. In this project fly and bottom ash from hard coal and domestic waste co-combustion were investigated on the occurrence and distribution of geochemical markers, polycyclic aromatic hydrocarbons (PAHs), and their alkyl derivatives. Hard coal with a domestic waste admixture (paper, ethylene propylene diene rubber, tire rubber, polyethylene, polyvinyl chloride) was combusted in a certified domestic central heating furnace equipped with a control and measurement system. Fly ash was collected on glass microfiber filters inside the flue gas chimney. Raw fuels, fly and bottom ash extracts were analyzed with gas chromatography–mass spectrometry (GC–MS). Geochemical markers survived the coal/domestic waste combustion and can be identified despite the presence of other organic compounds derived from domestic waste thermal decay. The highest changes in distribution and values of geochemical ratios concern light-weight compounds, i.e. lighter n-alkanes and acyclic isoprenoids (pristane and phytane), with distinct differences between fly and bottom ash. n-Alkanes expulsion significantly decreased values of Pr/n-C₁₇ and Ph/n-C₁₈ ratios. Due to their high molecular weight pentacyclic triterpanes mostly retained their original distributions; however, some shifts in values of their thermal maturity ratios occurred due to artificial maturation of organic matter under the heat of combustion. PAHs diagnostic ratios showed variable utility in the indication of domestic waste admixture to hard coal combusted. The highest sensitivity was found for BaP/BghiP, MPI-1, and MPI-3 whereas Fl/(Fl + Py) rather pointed out at hard coal dominating in the fuel mixture. The addition of EPDM and tires significantly worsened the quality of combustion, which is reflected in high extract yields and the retained hard coal geochemical features such as the Pr/Ph value closest to the raw coal value.