Biofuel production from pyrolysis of waste cooking oil fried sludge in a fixed bed

Waste cooking oil was used to dry sewage sludge by fry-drying technology. The obtained oil-fried sludge, which contained waste cooking oil and sewage sludge, was converted into biofuel simultaneously via pyrolysis process in a fixed bed. The synergistic effects of sewage sludge and waste cooking oil on the pyrolysis products were also investigated. Comparing to pyrolysis of sludge, pyrolysis of oil-fried sludge can obtain 51.9% higher gas products, where H2 and CH4 yields were increased by 37.4% (up to 211 ml/g) and 163% (up to 155 ml/g), respectively. The lower heating value (LHV) of gas product from oil-fried sludge was 41.2% higher than that from sludge. The higher LHV of gaseous products can be beneficial to use for power generation and heating. This indicates that oil-fried sludge shows a potential feedstock can be converted into high valuable biofuel. Nevertheless, the experimental gas and tar yield values of oil-fried sludge were lower than calculated values, indicating that there is an anergy effect of interactions between SS and oil on gas and tar formations. This was because the oily materials layer inhibited the heat and mass transfer in the sludge pyrolysis process, and then hindering the conversion of sludge into gas and tar formation.