Porous carbons derived from hydrothermally treated biogas digestate

Maria Bernardo, Catalina Rodriguez Correa, Yvonne Ringelspacher, Gero C. Becker, Nuno Lapa, Isabel Fonseca, Isabel A. A. C. Esteves, Andrea Kruse

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


Porous carbons from digestate-derived hydrochar were produced, characterized and their performance to reclaim phosphate from water was evaluated as a preliminary approach to demonstrate their practical application. In a first step, the digestate was converted into hydrochars through hydrothermal carbonization by using two different pH conditions: 8.3 (native conditions) and 3.0 (addition of H2SO4). The resulting hydrochars did not present significant differences. Consecutively, the hydrochars were activated with KOH to produce activated carbons with enhanced textural properties. The resulting porous carbons presented marked differences: the AC native presented a lower ash content (20.3 wt%) and a higher surface area (SBET = 1106 m2/g) when compared with the AC-H2SO4 (ash content = 43.7 wt% SBET = 503 m2/g). Phosphorus, as phosphate, is a resource present in significative amount in wastewater, causing serious problems of eutrophication. Therefore, the performance of the porous carbons samples to recover phosphate – P(PO4 3−) – from water was evaluated through exploitation assays that included kinetic studies. The lumped model presented a good fitting to the kinetic data and the obtained uptake capacities were the same for both carbons, 12 mg P(PO4 3−)/g carbon. Despite the poorer textural properties of AC-H2SO4, this carbon was richer in Ca, Al, Fe, K, and Mg cations which promoted the formation of mineral complexes with phosphate anions. The results obtained in this work are promising for the future development of P(PO4 3−) enriched carbons that can be used thereafter as biofertilizers in soil amendment applications.

Original languageEnglish
Pages (from-to)170-179
Number of pages10
JournalWaste Management
Publication statusPublished - 15 Mar 2020


  • Biogas production
  • Biomass digestate
  • Hydrothermal carbonization
  • Nanoporous carbons
  • Phosphate recovery from water


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