Roles of calcium oxide on the evolution of substituted polycyclic aromatic hydrocarbons released from sewage sludge pyrolysis

Substituted polycyclic aromatic hydrocarbons released from sewage sludge pyrolysis bring the concern of the clean utilization for the waste. Herein, the roles of calcium oxide on the release of these compounds, especially the heavy ones containing nitrogen and oxygen atoms were investigated. The results showed that calcium oxide significantly decreased light substituted polycyclic aromatic hydrocarbons in the volatiles from 450 to 850 degrees C and showed obvious inhibitory effects on the formation of heavy substituted polycyclic aromatic hydrocarbons at 850 degrees C. To understand the impact mechanisms, pyrolysis experiments of sludge model compounds lipid, protein and polysaccharides were conducted. It was found that calcium oxide could catalyze or react with all three components to decrease the content of light substituted polycyclic aromatic hydrocarbons. Heavy oxygencontaining aromatics in sludge derived volatiles mainly resulted from polysaccharides and protein, and they considerably decreased after mixing with calcium oxide. Oxygen-containing aromatics content in the lipid derived volatiles, however, would increase due to polymerization reactions. The decreasing release of nitrogen substituted polycyclic aromatic hydrocarbons from sludge could be attributed to the synergy effects of CaO and other minerals or the effects of CaO on the interaction between protein and other organics.

Automated summary

Calcium oxide has a significant impact on reducing the light substituted polycyclic aromatic hydrocarbons released from sewage sludge pyrolysis and inhibiting the formation of heavy ones. The mechanisms involve catalyzing or reacting with different components in the sludge model compounds to affect the content and formation of aromatics. The decrease in nitrogen substituted polycyclic aromatic hydrocarbons released from sludge can be attributed to the synergy effects of CaO and other minerals or the effects of CaO on the interaction between protein and other organics.