(2013) Chemosphere_Urban energy mining from sewage sludge

Kwon E.E., Yi H., Kwon H.H.

(Elsevier Ltd) Chemosphere ISSN: 456535 Vol.90 Issue.4 Article No. DOI: 10.1016/j.chemosphere.2012.07.062

This work showed that sewage sludge could be a strong candidate for biodiesel production. High lipid content (18-20%) with C_16-18-carbon range was experimentally identified and measured. These lipids from sewage sludge were converted into biodiesel via the transesterification reaction with MgO-CaO/Al₂O₃ derived from magnesium slag, and biodiesel conversion was ~98%. The experimental work enabled explaining that temperature is the main driving force for the transesterification reaction, which can be enhanced in the presence of CO₂. This also enables combination of esterification of free fatty acids and transesterification of triglycerides into a single process within 1min in the temperature range of 350-500°C. Sewage sludge residue after extracting lipids was also a good feedstock for recovering energy via thermo-chemical processes. The impact of CO₂ co-feed on the pyrolysis/gasification process of SS residue was also investigated in this work. The CO₂ injected into the thermo-chemical process remarkably increased the generation of CO by a factor of 2. Moreover, the introduction of CO₂ into the pyrolysis/gasification process enabled reducing condensable hydrocarbons (tar) by expediting cracking; thus, utilizing CO₂ as chemical feedstock for the gasification process not only leads to higher thermal efficiency but also has environmental benefits. © 2012 Elsevier Ltd.