Comparative study on the effect of different dewatering skeleton conditioners on sludge pyrolysis products

Abstract

Sewage sludge (SS) dehydration using skeleton conditioners is the main method of sludge treatment; however, the effects and mechanism of skeleton conditioning on pyrolysis products in the sludge conditioning–dehydration–pyrolysis process are still unclear. In this study, thermogravimetric mass spectrometry (TG-MS) and pyrolytic gas chromatography/mass spectrometry (Py-GC/MS) were used to study the release characteristics of condensable and non-condensable gases in the pyrolysis process of sludge samples treated with biochar (BC), rice husk (RH) and coal ash (CA), so as to clarify the effects of different skeleton conditioners on the pyrolysis products of sludge. The results indicate that the addition of RH promoted the generation of C/H/O-containing gases during pyrolysis. In terms of the release of pollutants, the addition of RH increased the release of NH3, the addition of CA increased the production of H2S and COS, and the addition of RH decreased the release of Cl2 and CH3Cl. The three skeleton conditioners did not noticeably promote or inhibit the release of S-containing pollutants during sludge pyrolysis. Several reaction kinetic models fitted using the Coats–Redfern method have shown that the addition of BC and CA had a certain catalytic effect on sludge pyrolysis, reducing the activation energy (Ea). By comprehensively comparing and analyzing the reaction mechanism of the skeleton conditioner in sludge pyrolysis and their influence on the pyrolysis products, a theoretical basis for future research on skeleton conditioners was developed to improve the dewatering and pyrolysis of SS.