Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Enhanced methanization of sewage sludge using an anaerobic membrane bioreactor integrated with hyperthermophilic biological hydrolysis Simon Mdondo Wandera a,b ,WeiQiao a,c, ⁎ , Mengmeng Jiang a,c , Ahmed Mahdy a,d , Dongmin Yin a,c , Renjie Dong a,c a College of Engineering, China Agricultural University, Beijing 100083, China b Department of Civil Engineering, Jomo Kenyatta University of Agriculture & Technology, Box 62000, Nairobi, Kenya c State R&D Center for Efficient Production and Comprehensive Utilization of Biobased Gaseous Fuels, Energy Authority, National Development, and Reform Committee, Beijing 100083, China d Department of Agricultural Microbiology, Zagazig University, 44511 Zagazig, Egypt ARTICLEINFO Keywords: Sewage sludge Anaerobic membrane bioreactor Hyperthermophilic hydrolysis Hydraulic retention time Membrane fouling ABSTRACT Highly efficient methanization of sewage sludge has been a long-standing challenge. Therefore, in this study, hyperthermophilic (70°C) biological hydrolysis pretreatment was investigated as a strategy to improve sludge biodegradability when subsequently combined with an anaerobic membrane bioreactor (AnMBR). Its effects on organics removal, methane yield, microbial community structure and activity were studied at hydraulic reten- tiontimes(HRTs)rangingfrom5to20days.Theresultsobtainedfromthe170-daycontinuouslyfedexperiment showedahighmethaneyield,rangingfrom176to246L/kg-VS in, intheAnMBRbyfeedingthepretreatedsludge ataconstantHRTof5days.Highremovalefficienciesofvolatilesolidsrangingfrom46%to63%occurredinthe AnMBR. A satisfactory net energy output was also obtained. Methanothermobacter dominated the AnMBR and was robust to the HRT changes. Severe membrane fouling occurred after 140days under a high solid con- centration. Subsequently, chemical cleaning (NaClO and citric acid) successfully recovered the flux and per- meability of the membrane. Conclusively, this study lays the foundation for using hyperthermophilic hydrolysis in the mechanization of sludge through integration with AnMBR technology. 1. Introduction Sewage sludge from domestic waste water treatment plants (WWTPs) has the potential for energy recovery as methane gas due to its organic matter content [1]. Anaerobic digestion (AD) of sewage sludge is a widely used technology for sludge treatment because of the relatively low capital and operational expenditure [2]. The mass of sludge generated in WWTPs can be reduced and methane recovered by anaerobic degradation of organic matter in sludge by various micro- organisms. The process comprises of four bioprocesses: hydrolysis, acidogenesis, acetogenesis and methanogenesis [3]. However, hydro- lysis,whichistheratelimingstepinconventionalADofsludge,andthe slow growth rate of methanogens, have posed a challenge in AD of sludge. Advances in sludge AD treatment are imperative to solve per- sistent problems such as the low rate of hydrolysis (i.e, pretreatment strategies) and the slow growth rate of methanogens (i.e, the decou- pling of hydraulic retention time (HRT) from solid retention time (SRT) to extend the retention of solids in the reactor) [4]. Hyperthermophilic biological hydrolysis pretreatment at a temperature range from 60 to 86°C has been intensively studied to improve the biodegradability of sludge [5,6].However,alingeringquestionofhowtofullyintegratethe improvements of the pretreated sludge with advanced anaerobic re- actor technology remains unanswered. The most widely used continuously stirred tank reactors (CSTR) require a large volume for AD and ordinarily operate at a longer HRT and a low organic loading rate (OLR) [7]. In comparison, the anaerobic membrane bioreactor (AnMBR) was developed by integrating mem- brane filtration with the anaerobic process to retain biomass inside the reactor. In an AnMBR, the treated liquid fraction is allowed to be quickly filtered through the membrane (microfiltration or ultrafiltra- tion), thus shortening the HRT, increasing the OLR, and successfully delinking HRT from SRT become achievable [8]. AnMBR technology has been reported as superior to traditional reactors for AD of organic matter treatment [9]. A reduced reactor size and increased methane yield under elevated organic loading rates have subsequently been re- ported when using AnMBR technology [5,7]. More specifically, https://doi.org/10.1016/j.enconman.2019.06.054 Received 9 May 2019; Received in revised form 19 June 2019; Accepted 20 June 2019 ⁎ Corresponding author. Postal address: P.O. Box 102, Qinghuadonglu Road, Haidian District, Beijing, China. E-mail address: qiaowei@cau.edu.cn (W. Qiao). Energy Conversion and Management 196 (2019) 846–855 0196-8904/ © 2019 Elsevier Ltd. All rights reserved. T