Life cycle assessment of prospective sewage sludge treatment paths in Germany

Felix Mayer; Ramchandra Bhandari; Stefan A Gäth

doi:10.1016/j.jenvman.2021.112557

Life cycle assessment of prospective sewage sludge treatment paths in Germany

J Environ Manage. 2021 Jul 15:290:112557. doi: 10.1016/j.jenvman.2021.112557. Epub 2021 Apr 14.

Authors

Felix Mayer¹, Ramchandra Bhandari², Stefan A Gäth³

Affiliations

¹ Institute for Technology and Resources Management in the Tropics and Subtropics (ITT), TH Köln (University of Applied Sciences), Germany. Electronic address: felix.mayer1@th-koeln.de.
² Institute for Technology and Resources Management in the Tropics and Subtropics (ITT), TH Köln (University of Applied Sciences), Germany.
³ Department of Agricultural Sciences, Nutritional Sciences and Environmental Management, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35392, Giessen, Germany.

PMID: 33865154
DOI: 10.1016/j.jenvman.2021.112557

Abstract

Due to the amendment of the sewage sludge ordinance, both a thermal post-treatment and a phosphorous recovery from sewage sludge will become mandatory for large-scale wastewater treatment plants in Germany. This study analyzed four prospective treatment paths for sewage sludge by means of life cycle assessment. In the realm of a gate-to-cradle approach, environmental impacts were quantified for all compartments of the ReCiPe Midpoint (H) 2016 method. The spreading of digested sludge on agricultural soils was considered as the base case (system: AD + spreading). It was compared to the centralized incineration of sludge (system: AD + I), a decentralized hydrothermal carbonization followed by centralized incineration (system: AD + HTC + I) and a decentralized pyrolysis of sludge followed by centralized incineration (system: AD + P + I). For all cases, phosphorous recovery from the ash was included. A comparative evaluation showed that AD + spreading resulted in least environmental impacts in most categories but was subject to a high local immission potential due to sewage sludge spreading. It was found to be only justifiable, if toxicity and eutrophication were not compromised. Alternatively, a thermal post-treatment step is required. Hereby, AD + I and AD + HTC + I showed the overall least environmental impacts, while AD + P + I was characterized by similar or higher environmental impacts throughout all impact categories. Alongside the comparative analysis, a hotspot analysis was carried out and mitigation potentials were identified. For all thermochemical post-treatment paths, it was derived that (i) the share of fossil external energy must be kept to a minimum, (ii) primary or secondary measures to control N₂O emissions during the incineration and pyrolysis should be implemented and (iii) the technological approach to recover phosphorous must be carefully selected.

Keywords: Hydrothermal carbonization; Incineration; Life cycle assessment; Phosphorous recovery; Pyrolysis; Sewage sludge.

MeSH terms

Animals
Germany
Incineration*
Life Cycle Stages
Prospective Studies
Sewage*

Substances

Sewage