Wet oxidation of aqueous phase from hydrothermal liquefaction of sewage sludge

Lars Bjørn Silva Thomsen; Konstantinos Anastasakis; Patrick Biller

doi:10.1016/j.watres.2021.117863

Wet oxidation of aqueous phase from hydrothermal liquefaction of sewage sludge

Water Res. 2022 Feb 1:209:117863. doi: 10.1016/j.watres.2021.117863. Epub 2021 Nov 16.

Authors

Lars Bjørn Silva Thomsen¹, Konstantinos Anastasakis¹, Patrick Biller²

Affiliations

¹ Department of Biological and Chemical Engineering, Aarhus University, Hangøvej 2, Aarhus N 8200, Denmark; WATEC - Centre for Water Technology, Aarhus University, Ny Munkegade 120, Aarhus 8000, Denmark.
² Department of Biological and Chemical Engineering, Aarhus University, Hangøvej 2, Aarhus N 8200, Denmark; WATEC - Centre for Water Technology, Aarhus University, Ny Munkegade 120, Aarhus 8000, Denmark. Electronic address: pbiller@bce.au.dk.

PMID: 34844067
DOI: 10.1016/j.watres.2021.117863

Abstract

Hydrothermal liquefaction (HTL) is a thermochemical process for the conversion of biomass into bio-crude oil. However, treatment of post-HTL aqueous by-products is an emerging issue towards the commercialisation of HTL technology. This study investigates the use of non-catalytic wet oxidation (WO) for the reduction of organic compounds and heat production at different temperatures (200-350 °C), residence times (RT) (2-180 min) and excess oxygen. The aqueous phase from HTL of sewage sludge is investigated, and 97.6% of the chemical oxygen demand (COD) and 96.1% of the total organic carbon (TOC) were removed at the highest temperature and retention time. The minimum energy requirement achieved was 9.6 kWh/kg COD removed at 200 °C for 180 min, and the exothermic reactions of the process can generate 28.3% of the required heat. GC-FID and -MS analysis revealed that the degradation of different groups of organic compounds generates acetic acid as an intermediate by-product of WO, being further oxidised at temperatures higher than 300 °C. NH₄⁺and NH₃ are generated from the decomposition of nitrogenated organic compounds showing the highest concentration of 704.5 mg _NH4+ /L at 350 °C after 180 min.

Keywords: Aqueous phase; Hydrothermal liquefaction; Sewage sludge; Wet oxidation.