title: Co-gasification of sewage sludge and woody biomass in a fixed-bed downdraft gasifier: toxicity assessment of solid residues.
abstract: As the demand for fossil fuels and biofuels increases, the volume of ash generated will correspondingly increase. Even though ash disposal is now strictly regulated in many countries, the increasing volume of ash puts pressure on landfill sites with regard to cost, capacity and maintenance. In addition, the probability of environmental pollution from leakage of bottom ash leachate also increases. The main aim of this research is to investigate the toxicity of bottom ash, which is an unavoidable solid residue arising from biomass gasification, on human cells in vitro. Two human cell lines i.e. HepG2 (liver cell) and MRC-5 (lung fibroblast) were used to study the toxicity of the bottom ash as the toxins in the bottom ash may enter blood circulation by drinking the contaminated water or eating the food grown in bottom ash-contaminated water/soil and the toxic compounds may be carried all over the human body including to important organs such as lung, liver, kidney, and heart. It was found that the bottom ash extract has a high basicity (pH = 9.8-12.2) and a high ionic strength, due to the presence of alkali and alkaline earth metals e.g. K, Na, Ca and Mg. Moreover, it also contains concentrations of heavy metals (e.g. Zn, Co, Cu, Fe, Mn, Ni and Mo) and non-toxic organic compounds. Although human beings require these trace elements, excessive levels can be damaging to the body. From the analyses of cell viability (using MTS assay) and morphology (using fluorescence microscope), the high toxicity of the gasification bottom ash extract could be related to effects of high ionic strength, heavy metals or a combination of these two effects. Therefore, our results suggest that the improper disposal of the bottom ash wastes arising from gasification can create potential risks to human health and, thus, it has become a matter of urgency to find alternative options for the disposal of bottom ash wastes.
authors.affiliation: NUS Environmental Research Institute, National University of Singapore, 1 Create Way, Create Tower #15-02, Singapore 138602, Singapore.
authors.forename: Le
authors.initials: L
authors.lastname: Rong
authors.affiliation: NUS Environmental Research Institute, National University of Singapore, 1 Create Way, Create Tower #15-02, Singapore 138602, Singapore.
authors.forename: Thawatchai
authors.initials: T
authors.lastname: Maneerung
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.
authors.forename: Jingwen Charmaine
authors.initials: JC
authors.lastname: Ng
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore. Electronic address: chenkg@nus.edu.sg.
authors.forename: Koon Gee
authors.initials: KG
authors.lastname: Neoh
authors.affiliation: Department of Anatomy, Yong Loo Lin School of Medicine, National University Health System, 4 Medical Drive, Singapore 117597, Singapore.
authors.forename: Boon Huat
authors.initials: BH
authors.lastname: Bay
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.
authors.forename: Yen Wah
authors.initials: YW
authors.lastname: Tong
authors.affiliation: School of Mechanical Engineering, Shanghai Jiaotong University, Shanghai 200240, China.
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Dai
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore. Electronic address: chewch@nus.edu.sg.
authors.forename: Chi-Hwa
authors.initials: CH
authors.lastname: Wang
mesh_terms: D002460:Cell Line; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects*; D060729:Coal Ash / Q000633:toxicity*; D056945:Hep G2 Cells; D006801:Humans; D017745:Incineration; D008670:Metals / Q000633:toxicity; D009930:Organic Chemicals / Q000633:toxicity; D011084:Polycyclic Aromatic Hydrocarbons / Q000633:toxicity; D012037:Refuse Disposal; D012722:Sewage; D014934:Wood / Q000633:toxicity*
chemical_list: D060729:Coal Ash; D008670:Metals; D009930:Organic Chemicals; D011084:Polycyclic Aromatic Hydrocarbons; D012722:Sewage
keywords: Bottom ash; Downdraft gasifier; Gasification; Sewage sludge; Toxicity assessment