The determination of pyrolytic synergies between sewage sludge and low-rank coal

Abstract

In this study, South African sewage sludge (SASS) and turnout North American lignite (NAL) were subjected to analytical pyrolysis and evaluation of synergistic interaction. Mineralogical and chemical properties of the SASS, NAL, SASS and NAL blends and their ashes differed significantly owing to the origin of the samples evaluated . Fourier-transform infrared spectroscopy results showed that both samples comprised of similar functional groups with different transmittance intensities. NAL projected a high hydroxyl intensity at 3500-2800 cm− 1 , corresponding to its higher moisture content and the OH- from kaolinite. The organic matrices of both SASS and NAL consisted mainly of long length-chain fatty acids and long-oil range hydrocarbons (C > 15), but NAL reported a slightly higher elution time owing to signatures of a number of complex aromatic compounds and substitutions such as phenol, naphthalene, glycol and plasticiser (phthalate) compounds. The thermogravimetric analysis indicated that NAL thermal degradation took place over a wider temperature range starting from 350 to 700 ◦C, while SASS thermal-degradation occurred between 250 and 500 ◦C. Also, a slower NAL decomposition rate related to the higher concentration of long-chain hydrocarbons and formation of aromatic clusters via secondary repolymerization reaction as indicated by NMR. The slow decomposition rate and repolymerization reaction contributed to higher activation energy(Ea) requirements for NAL pyrolysis. Interactive blend ratios for the thermal degradation were found to be 80 %SASS:20 %NAL and 20 %SASS:80 %NAL with Ea of 285.24 and 415.72 kJ/mol, respectively. Results obtained from this work provide a starting point towards co-pyrolysis of digested SASS with South African fine coal rejects. Utilization of sewage sludge and fine coal wastes in the thermochemical processes could have potential for fuel production as well as resolving environmental and Human health problems associated with high-cost waste disposal methods.