Ionic liquid catalyzed low-temperature hydrothermal carbonization of sewage sludge to produce hydrochar with low heavy metal content and positive energy recovery

Liming Liu; Hongxia Wang; Wei Zou; Luna Zhao; Fashen Liang; Yunbo Zhai

doi:10.1016/j.biortech.2024.130803

Ionic liquid catalyzed low-temperature hydrothermal carbonization of sewage sludge to produce hydrochar with low heavy metal content and positive energy recovery

Bioresour Technol. 2024 May 10:402:130803. doi: 10.1016/j.biortech.2024.130803. Online ahead of print.

Authors

Liming Liu¹, Hongxia Wang², Wei Zou², Luna Zhao², Fashen Liang², Yunbo Zhai³

Affiliations

¹ College of Environmental Science and Engineering, Hunan University, Changsha 410082, P.R. China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P.R. China; Department of Civil and Earth Resources Engineering, Kyoto University, Kyoto 612-8236, Japan.
² College of Environmental Science and Engineering, Hunan University, Changsha 410082, P.R. China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P.R. China.
³ College of Environmental Science and Engineering, Hunan University, Changsha 410082, P.R. China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, P.R. China. Electronic address: ybzhai@hnu.edu.cn.

PMID: 38734263
DOI: 10.1016/j.biortech.2024.130803

Abstract

An ionic liquid (IL, [DMAPA]HSO₄) was prepared to facilitate the removal of heavy metals by hydrothermal carbonization (HTC) in sewage sludge (SS) and to obtain a positive energy recovery (ER, (Energy_output/Energy_input - 1) > 0). The results found that the removal efficiencies of the Fe, Mn, Zn, Co, and Cd from SS exceeded 75 % with positive ER (6 %) at 20 wt% IL dosage (IL:SS). IL promoted the HTC reactions of proteins and polysaccharides to produce fixed carbon and small molecule polymers. The process mainly relies on IL to catalyze the dehydration and graphitization of SS and to destroy the heavy metal binding sites such as carboxyl and hydroxyl groups. Additionally, IL aids in constructing the macropore structures in hydrochar, thereby facilitating the release of heavy metals and water during the HTC process. This discovery holds promise for removing heavy metals from SS by one-pot HTC processes with positive energy recovery.

Keywords: Biofuel; Biomass; Clean energy; Energy recovery; Metal removal.