Hydrothermal Carbonization of Sewage Sludge: New Improvements in Phosphatic Fertilizer Production and Process Water Treatment Using Freeze Concentration

Gabriel Gerner (), Jae Wook Chung, Luca Meyer, Rahel Wanner, Simon Heiniger, Daniel Seiler, Rolf Krebs, Alexander Treichler, Roman Kontic and Beatrice Kulli
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Gabriel Gerner: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Jae Wook Chung: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Luca Meyer: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Rahel Wanner: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Simon Heiniger: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Daniel Seiler: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Rolf Krebs: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland
Alexander Treichler: Institute of Chemistry and Biotechnology, Zurich University of Applied Sciences (ZHAW), Campus Reidbach, CH-8820 Wädenswil, Switzerland
Roman Kontic: School of Engineering, Zurich University of Applied Sciences (ZHAW), CH-8401 Winterthur, Switzerland
Beatrice Kulli: Institute of Natural Resource Sciences, Zurich University of Applied Sciences (ZHAW), Campus Grüental, CH-8820 Wädenswil, Switzerland

Energies, 2023, vol. 16, issue 20, 1-19

Abstract: In recent years, promising developments in the hydrothermal carbonization (HTC) of sewage sludge, as well as the potential to reclaim phosphorus and nitrogen, have emerged. In this study, the HTC of digested sewage sludge (DSS) was investigated for the downstream production of heavy metal (HM)-free fertilizer and the use of freeze concentration (FC) as a novel technology for process water treatment. To obtain clean fertilizer, phosphatic acid extracts were first treated with ion-exchange resins to remove dissolved HM, as well as phosphorus precipitating agents (i.e., aluminum and iron). Over 98% of the aluminum (Al) and 97% of the iron (Fe) could be removed in a single treatment step. The purified extract was then used for the precipitation of HM-free struvite crystals, with P-recovery rates exceeding 89%. Process water (PW) makes up the largest share of the two main HTC-products (i.e., hydrochar and PW) and is very rich in organic compounds. Compared to evaporation or membrane separation, FC is a promising technology for concentrating solutes from PW. Separation experiments resulted in the recovery of over 90% of the dissolved compounds in the concentrate. In our study, the concentrate was later utilized as an ammonium source for struvite precipitation, and the subsequent aerobic digestion of the remaining ice water resulted in an 85% reduction in chemical oxygen demand (COD) in 15 days.

Keywords: hydrothermal carbonization; digested sewage sludge; hydrochar; phosphorus recovery; nutrient recovery; recycling fertilizer; ion exchanger; process water treatment; freeze concentration (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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