Effect of hydrothermal treatment on deep dewatering of digested sludge: Further understanding the role of lignocellulosic biomass

Majid Ebrahimi; Kameron Dunn; Huan Li; David W Rowlings; Ian M O'Hara; Zhanying Zhang

doi:10.1016/j.scitotenv.2021.152294

Effect of hydrothermal treatment on deep dewatering of digested sludge: Further understanding the role of lignocellulosic biomass

Sci Total Environ. 2022 Mar 1:810:152294. doi: 10.1016/j.scitotenv.2021.152294. Epub 2021 Dec 11.

Authors

Majid Ebrahimi¹, Kameron Dunn¹, Huan Li², David W Rowlings³, Ian M O'Hara¹, Zhanying Zhang⁴

Affiliations

¹ Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, 2 George Street, Brisbane, Queensland 4000, Australia; School of Mechanical, Medical and Process Engineering, Faculty of Engineering, Queensland University of Technology, 2 George Street, Brisbane, Queensland 4000, Australia.
² Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China.
³ Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, 2 George Street, Brisbane, Queensland 4000, Australia; School of Biology and Environmental Science, Faculty of Science, Queensland University of Technology, 2 George Street, Brisbane, Queensland 4000, Australia.
⁴ Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, 2 George Street, Brisbane, Queensland 4000, Australia; School of Mechanical, Medical and Process Engineering, Faculty of Engineering, Queensland University of Technology, 2 George Street, Brisbane, Queensland 4000, Australia. Electronic address: jan.zhang@qut.edu.au.

PMID: 34906581
DOI: 10.1016/j.scitotenv.2021.152294

Abstract

In this study, lignocellulose-assisted hydrothermal treatment (HTT) of digestated sludge was studied to further understand the role of biomass in HTT and its effect on subsequent sludge dewatering. HTT of sludge-biomass mixtures at 180 °C for 60 min at a sludge/biomass total solids (TS) ratio of 1:1 led to solid residue moistures of 36%-40% after dewatering using a hydraulic press at 24 MPa, compared to 69.5% without biomass. Further investigation showed that organic acids, especially acetic acid generated from lignocellulosic biomass hydrolysed extracellular polymeric substances (EPS), especially EPS-protein, and improved sludge dewaterability. The role of organic acids was further verified with the addition of 10.0 g/L acetic acid for HTT of sludge at 180 °C in the absence of biomass. It was also observed that in HTT of sludge with 10.0 g/L acetic acid, protein nitrogen was converted to more stable forms of nitrogen such as pyrrole‑nitrogen and quaternary‑nitrogen. However, HTT with acetic acid alone resulted in dewatered solids with high ash contents, which may limit their applications as soil amendments. Combination of biomass and acetic acid with a sludge/biomass TS ratio of 3:1 and acetic acid loading of 10.0 g/L at a HTT temperature of 180 °C for 60 min led to solid moistures of 50.5% with hardwood sawdust and 57.7% with sugarcane bagasse after dewatering at 3 MPa, corresponding to total weight reductions of 66.3% and 55.7%, respectively. In contrast, HTT of sludge at 180 °C for 60 min without acetic acid and biomass resulted in a solid moisture of 76.6% after dewatering at 3 MPa and a corresponding weight reduction of 49.5%. With the use of biomass and acetic acid in HTT, the treated and dewatered solids also had increased carbon content and reduced ash content. These dewatered solids may be used as potential soil amendments though the properties related to soil applications need to be considered in future studies.

Keywords: Acetic acid; Biomass; Dewatering; Hydrothermal treatment; Sludge.

MeSH terms

Biomass
Lignin*
Sewage*
Temperature
Waste Disposal, Fluid
Water

Substances

Sewage
Water
lignocellulose
Lignin