The performance and microbial response of zero valent iron alleviating the thermal-alkaline stress and enhancing hydrolysis-acidification of primary sludge

Abstract

The biological thermal-alkaline hydrolysis-acidification (BTAHA) could promote sludge disintegration, which was conducive to producing volatile fatty acids (VFAs). However, high temperature and strong alkali could reduce the BTAHA effluent quality. Because high temperature denatures proteins and significantly changes the material and energy metabolism of bacteria, while strong alkali inhibits fermentation microorganisms (especially acid-producing microorganisms). This study investigated the internal mechanism of zero valent iron (ZVI) and magnetite (Mag.) alleviating temperature and alkali stress and improving the quality of hydrolysis-acidification effluent. At pH 7-10, compared with the control and magnetite, ZVI increased the average effluent VFAs by 24.0%-40.1% and 11.6%-18.1%, respectively. At pH 9, ZVI could provide an ecological niche for acidifying bacteria that preferred neutral and weakly alkaline conditions, with a 49.8% proportion of VFAs to soluble chemical oxygen demand (SCOD). At pH 12, the fluorescence intensity ratio of easy to difficult biodegradable organic matter in control, R_Mag., and R_ZVI were 0.63, 0.62, and 1.31, respectively. It indicated ZVI effectively alleviated high temperature and strong alkali stress. This study provides a reference for improving the quality of BTAHA effluent.

Keywords: Anaerobic fermentation; Iron-based materials; Primary sludge; Thermal-alkaline; pH.