Effects of lignocellulosic biomass type on the economics of hydrothermal treatment of digested sludge for solid fuel and soil amendment applications

Majid Ebrahimi; Jerome A Ramirez; John G Outram; Kameron Dunn; Paul D Jensen; Ian M O'Hara; Zhanying Zhang

doi:10.1016/j.wasman.2022.11.020

Effects of lignocellulosic biomass type on the economics of hydrothermal treatment of digested sludge for solid fuel and soil amendment applications

Waste Manag. 2023 Feb 1:156:55-65. doi: 10.1016/j.wasman.2022.11.020. Epub 2022 Nov 24.

Authors

Majid Ebrahimi¹, Jerome A Ramirez², John G Outram², Kameron Dunn², Paul D Jensen³, Ian M O'Hara², Zhanying Zhang⁴

Affiliations

¹ Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, Brisbane, Queensland 4000, Australia; School of Mechanical, Medical, and Process Engineering, Faculty of Engineering, Queensland University of Technology, Brisbane, Queensland 4000, Australia. Electronic address: majid.ebrahimi@hdr.qut.edu.au.
² Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, Brisbane, Queensland 4000, Australia; School of Mechanical, Medical, and Process Engineering, Faculty of Engineering, Queensland University of Technology, Brisbane, Queensland 4000, Australia.
³ Australian Centre for Water and Environmental Biotechnology, The University of Queensland, St. Lucia, Queensland 4072, Australia.
⁴ Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, Brisbane, Queensland 4000, Australia; School of Mechanical, Medical, and Process Engineering, Faculty of Engineering, Queensland University of Technology, Brisbane, Queensland 4000, Australia. Electronic address: jan.zhang@qut.edu.au.

PMID: 36436408
DOI: 10.1016/j.wasman.2022.11.020

Abstract

Digested sludge is a waste stream from anaerobic digestion (AD) in wastewater treatment plants. Hydrothermal treatment (HTT) of sludge mixed with lignocellulosic biomass is an attractive approach to improve sludge dewaterability and generate value-added products. However, process economics has not been well understood. In this study, firstly, the effect of biomass type on the energy properties of hydrochars was studied. Secondly, two scenarios were simulated to evaluate the effects of biomass type on the economics (processing 50,000 tonnes of sludge per year) of HTT of digested sludge for solid fuel and soil amendment applications. The two HTT scenarios included sludge alone and sludge-biomass mixtures (four cases for four biomass feedstocks) at 180 °C for 60 min. In both scenarios, HTT liquids were returned to existing AD facilities for biomethane production to offset the energy cost of the HTT process. The results showed that the higher heating value significantly increased from 16.0-17.0 MJ kg^-1 in the sludge alone case to 18.0-23.0 MJ kg^-1 in sludge-biomass mixtures (except for rice husk). With the use of saved transport cost as a revenue source, HTT of sludge-biomass led to a net present value (NPV) range of AU$ 9.9-20.3 million (20 years) and an internal rate of return (IRR) range of 25.0 %-45.2 % for solid fuel application of resulting hydrochar compared to an NPV of AU$ 18.4 million and an IRR of 55.0 % from HTT of sludge alone scenario. HTT of sludge-biomass led to a NPV range of AU$ 4.5-14.5 million and an IRR range of 17.2 %-35.7 % for soil amendment application while the hydrochar from HTT of sludge alone was not recommended for soil application due to the high contents of heavy metals. This study provides useful and critical information for process scale-up and commercialization for integration into wastewater treatment plants.

Keywords: Biomass; Hydrochar; Hydrothermal Treatment; Sludge; Techno-economic Analysis.

MeSH terms

Biomass
Carbon
Metals, Heavy*
Sewage*
Soil
Temperature

Substances

Sewage
Soil
lignocellulose
Metals, Heavy
Carbon