The Research On The Co-liquefaction Of Sewage Sludge And Oil-tea-cake In Supercritical Methanol: Yield Of Bio-oil, Risk Assessment Of Heavy Metals

With the acceleration of urbanization, diminishing petroleum fuel supplies and adverse environmental impacts has seriously impeded the development of the city,prompted considerable interest in research and development of green and renewable energy resources. Biodiesel is one of the most attractive alternative energy sources because of its good combustion properties, renewable and environment-friendly features. Sewage sludge is generated from the wastewater treatment process, the treatment and the disposal of which has become a worldwide problem. On the one hand, a variety of toxic and hazardous substances in sewage sludge may produce a potential threat on human health and the environment. On the other hand, municipal sludge contains large amounts of organic matter, organic matter content accounted for more than 30% of dry organic matter, increased the demand of technology for sludge treatment and disposal. Conventional sludge treatment and disposal methods have been unable to meet environmental requirements, therefore, finding new treatment and disposal ways to reduction, stability, development of resources technology methods has become a growing concern.This article studied the supercritical liquefaction process of sewage sludge which use the main experimental apparatus is an intermittent autoclave. The experiment revealed influence of temperature, resistant time, heating rate and catalyst to the yields of bio-oil, use the GC-MS and elemental analyzer to analysis the reaction produact.Focus on the toxicities of heavy metals(HMs) in liquefaction residues(LRs), explores the effect of co-liquefaction of sewage sludge and oil-tea-cake.In this study, attentions were focused on the yield of bio-oil and toxicity of heavy metals in liquefaction residue. Liquefaction of sewage sludge(SS) or oil-tea-cake(OTC) or mixtures of SS and OTC were carried out under the condition of supercritical methanol in an intermittent high pressure autoclave. Results showed that the addition of OTC extraordinarily increased the yields of oil from 37.9%(SS) to 86.2%(SS +OTC). Furthermore, with the liquefaction of SS and OTC mixture, the bioavailable fraction(F1 + F2) of Cd and Cu(F1 + F2) was decreased. However, the bioavailable fraction of Zn(F1 + F2) increased. Risk assessments of geo-accumulation index(Igeo),risk assessment code(RAC) and modified potential ecological risk index(MRI) were applied to evaluate the bioavailabilities, the potential ecological risks and the pollution levels of HMs. The results show that the addition of OTC in supercritical liquefaction of SS can decrease the risk of HMs in LRs.Results show that the addition of OTC to SS can not only reduce the risk of heavy metals in LRs but also enhance the conversion of SS, implying synergistic effects of OTC and SS. Liquefaction of SS and OTC mixtures could be used as a promising approach to deal with SS. The conclusion of this study provides reference and theoretical basis for technical improvement, optimization, and laid the foundation for further development of biodiesel industry.