an official journal of: published by:
an official journal of: published by:
Editor in Chief: RAFFAELLO COSSU


  • Tommy Ender - Department of Waste and Resource Management, Faculty of Agricultural and Environmental Sciences, University of Rostock, Germany
  • Vicky Shettigondahalli Ekanthalu - Department of Waste and Resource Management, Faculty of Agricultural and Environmental Sciences, University of Rostock, Germany
  • Michael Nelles - DBFZ, the German Centre for Biomass Research , Germany

Access restricted to subscribed members only

Released under All rights reserved

Copyright: © 2023 CISA Publisher


As the result of new regulation from the German Sewage Sludge Ordinance (AbfKlärV 2017) and the future obligation to recover phosphorus, thermal treatment (mono-incineration) has become increasingly popular, whereas land-based utilization has decreased. Germany has produced 1.71 million metric tons (DM) of sewage sludge in the year 2021. Sewage sludge contains important nutrients such as phosphorus but also heavy metals and organic pollutants making the direct utilization of sewage sludge in agriculture controversial. Rural areas in particular have benefited from land-based sewage sludge utilization however the future ban on direct land-based utilization is forcing them to find alternative solutions for sewage sludge treatment and management. Hydrothermal carbonization (HTC) has developed considerably over the last 15 years and offers a viable alternative for the utilization of municipal and industrial organic waste such as sewage sludge. The process takes place in an aqueous environment without the need for pre-drying sewage sludge and thereby facilitating direct processing. HTC is especially suitable in combination with the recovery of nutrients like phosphorus. Technologies to recover this essential resource are important because phosphorus is an element that cannot be substituted and is therefore essential. HTC could make a significant contribution to sewage sludge management in combination with phosphorus recovery. However, the technology has yet to establish itself as a sewage sludge valorization process (2023) and is not yet a recognized state-of-the-art. Nevertheless, the HTC technology could gain greater relevance in the future, especially as an alternative valorization pathway for sewage sludge in rural areas of Germany.


Editorial History

  • Received: 02 Feb 2023
  • Revised: 27 Jul 2023
  • Accepted: 04 Aug 2023
  • Available online: 30 Sep 2023


Aragón-Briceño, C. I., Pozarlik, A. K., Bramer, E. A., Niedzwiecki, L., Pawlak-Kruczek H., Brem, G., 2021. Hydrothermal carbonization of wet biomass from nitrogen and phosphorus approach: A review, Renewable Energy, Volume 171, 401-415.
DOI 10.1016/j.renene.2021.02.109

Asghari, F. S., Yoshida, H., 2006. Acid-Catalyzed Production of 5-Hydroxymethyl Furfural from d-Fructose in Subcritical Water. Ind. Eng. Chem. Res. 2006, 45, 7, 2163–2173.
DOI 10.1021/ie051088y

AVA-CO2 Schweiz AG. 2014. “AVA-CO2 Achieves a Breakthrough in Phosphorus Recovery and Introduces the “AVA cleanphos” Process.” September. Accessed May 2023.

Basse, S., Buck, P., Domschke, T., Elstermann, N., Esser, R., Hanßen, H., Haselwimmer, T., Hiller, G., Jasper, M., Kappa, S., Kristkeitz, R., Lehrmann, F., Ludwig, P., Maurer, M., Ostertag, M., Peters, U., Pietsch, B., Steier, K., Werther, J., Wessel, M., Nath, C., Reifenstuhl, R., 2012. Merkblatt DWA-M 387 Thermische Behandlung von Klärschlämmen – Mitverbrennung in Kraftwerken. DWA Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e. V

Blach, T., Engelhart, M., 2020. Optimizing the Hydrothermal Carbonization of Sewage Sludge—Response Surface Methodology and the Effect of Volatile Solids. Water, 13 (9), p. 1225.
DOI 10.3390/w13091225

Blöhse, D., 2017. Hydrothermale Karbonisierung – Nutzen dieser Konversionstechnik für die optimierte Entsorgung feuchter Massenreststoffe (Doctoral dissertation). University Essen, Germany: Duisburg-Essen. Retrieved from

Bozkurt, S., Moreno, L., Neretnieks, I., 2000. Long-Term Processes in Waste Deposits. Science of the Total Environment, 250, 101-121.
DOI 10.1016/S0048-9697(00)00370-3

Buttmann, M., 2023. TerraNova®ultra project for sewage sludge and biowaste in Poland. Retrieved from Last retrieved 31.05.2023

Chen, H., Rao, Y., Cao, L., Shi, Y., Hao, S., Lou, G., Zhang, S., 2019. Hydrothermal conversion of sewage sludge: Focusing on the characterization of liquid products and their methane yields. Chemical Engineering Journal, Volume 357, 2019, Pages 367-375.
DOI 10.1016/j.cej.2018.09.180

Crocker, M., 2011. Thermo chemical Conversion of Biomass to Liquid Fuels and chemicals. Royal Society of Chemistry Publishing.
DOI 10.1039/9781849732260

Danso-Boateng, E., Sharma, G., Wheatly, A. D., Martin, S. J., Holdich, R. G., 2015. Hydrothermal carbonisation of sewage sludge: Effect of process conditions on product characteristics and methane production. Bioresource Technology, Volume 177, 2015. 318-327.
DOI 10.1016/j.biortech.2014.11.096

Djandja, O. S., Yin, L., Wang, Z.-C., Duan, P.-G., 2021. From wastewater treatment to resources recovery through hydrothermal treatments of municipal sewage sludge: A critical review. Process Safety and Environmental Protection, 151, 101–127.
DOI 10.1016/j.psep.2021.05.006

Ehrnström, Matilda Sirén. 2016. “Recovery of Phosphorus from HTC Converted Municipal Sewage Sludge.” MASTER OF SCIENCE THESIS, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology

Ekpo, U., Ross, A. B., Camargo-Valero, M. A., Fletcher, L. A., 2016. Influence of pH on hydrothermal treatment of swine manure: Impact on extraction of nitrogen and phosphorus in process water. Bioresource Technology, Volume 214, 2016, Pages 637-644.
DOI 10.1016/j.biortech.2016.05.012

Geng, H., Xu, Y., Zheng, L., Gong, H., Dai, L., Dai, X., 2020. An overview of removing heavy metals from sewage sludge: Achievements and perspectives. Environmental Pollution, Volume 266, Part 2, 115375.
DOI 10.1016/j.envpol.2020.115375

Gerner, G., Meyer, L., Wanner, R., Keller, T., Krebs, R. (2021): Sewage Sludge Treatment by Hydrothermal Carbonization: Feasibility Study for Sustainable Nutrient Recovery and Fuel Production. Energies 2021, 14, 2697.
DOI 10.3390/en14092697

Heckenmüller, M., Narita, D., Klepper, G., 2014. Global availability of phosphorus and its implications for global food supply: An economic overview, Kiel Institute for the World Economy (IfW), Kiel

Huang, R, Fang, C., Zhang, B., Tang, Y., 2018. Transformations of Phosphorus Speciation during (Hydro)thermal Treatments of Animal Manures. Environ. Sci. Technol. 52 (5): 3016-3026.
DOI 10.1021/acs.est.7b05203

Huezo, L., Vasco-Correa, J., Shah, A., 2021. Hydrothermal carbonization of anaerobically digested sewage sludge for hydrochar production. Bioresource Technology Reports, Volume 15, 2021, 100795.
DOI 10.1016/j.biteb.2021.100795

Kambo, H. S., Minaret, J., Dutta, A. (2018): Process Water from the Hydrothermal Carbonization of Biomass: A Waste or a Valuable Product?. Waste Biomass Valor 9, 1181–1189 (2018).
DOI 10.1007/s12649-017-9914-0

Klärschlammverordnung (AbfKlärV) vom 27. September 2017 (BGBl. I S. 3465), die zuletzt durch Artikel 137 der Verordnung vom 19. Juni 2020 (BGBl. I S. 1328) geändert worden ist

Krüger, O., Adam, C., 2015. Recovery potential of German sewage sludge ash, Waste Management, Volume 45, 2015, 400-406.
DOI 10.1016/j.wasman.2015.01.025

Kruse, A., Funke, A., Titirici, M.-M., 2013. Hydrothermal conversion of biomass to fuels and energetic materials. Current Opinion in Chemical Biology, Volume 17, Issue 3, 2013, 515-521.
DOI 10.1016/j.cbpa.2013.05.004

Kwapinski, W., Kolinovic, I., Leahy, J.J., 2021. Sewage Sludge Thermal Treatment Technologies with a Focus on Phosphorus Recovery: A Review. Waste Biomass Valor 12, 5837–5852.
DOI 10.1007/s12649-020-01280-2

Langenohl, T., 2015. Auswirkungen der sich verändernden Rahmenbedingungen auf die Entsorgungssicherheit für Klärschlamm. KA Korrespondenz Abwasser, Abfall, Jahrgang 62, Heft 3, 249-256.
DOI 10.3242/kae2015.03.003

Leng, L., Zhang, W., Leng, S., Chen, J., Yang, L., Li, H., Jiang, S., Huang, H., 2020: Bi.oenergy recovery from wastewater produced by hydrothermal processing biomass_Progress, challenges, and opportunities. Science of The Total Environment, Volume 748, 2020, 142383,
DOI 10.1016/j.scitotenv.2020.142383

Li, F., Ji, W., Chen, Y., Gui, X., Li, J., Zhao, J., Zhou, C., 2021. Effect of Temperature on the Properties of Liquid Product from Hydrothermal Carbonization of Animal Manure and Function as a Heavy Metal Leaching Agent in Soil. Water Air Soil Pollut 232, 189 (2021).
DOI 10.1007/s11270-021-05134-y

Libra, J. A., Ro, K. S., Kammann, C., Funke, A., Berge, N. D., Neubauer, Y., Titirici, M.-M., Fühner, C., Bens, O., Kern, J., 2011. Hydrothermal carbonization of biomass residuals: a comparative review of the chemistry, processes and applications of wet and dry pyrolysis. Biofuels 2(1):71–106.
DOI 10.4155/bfs.10.81

Liu, T., Liu, Z., Zheng, Q., Lang, Q., Xia, Y., Peng, N., Gai, C., 2018. Effect of hydrothermal carbonization on migration and environmental risk of heavy metals in sewage sludge during pyrolysis. Bioresour Technol 247:282–290.
DOI 10.1016/j.biortech.2017.09.090

Malhotra, M. and Garg, A., 2020. Hydrothermal carbonization of centrifuged sewage sludge: Determination of resource recovery from liquid fraction and thermal behaviour of hydrochar. Waste Management, Volume 117, November 2020, 114-123.
DOI 10.1016/j.wasman.2020.07.026

Mix-Spagl, K., 2017. Die neue Klärschlammverordnung – Was müssen Betreiber beachten? - Special Klärschlamm - Recht & Gesetz, 2017, 10, 15-17

Montag, D., Adam, C., Baumann, P., Frank, D., Kabbe, C., Klein, D., Meyer, C., Mocker, M., Morf, L., Pinnekamp, J., Roskosch, A., Schaum, C., Schneichel, W., Schneider, Y., Wett, M., Arnold, U., Heidecke, P., Sichler, T., 2022. Rechtliche Vorgaben der Klärschlammverordnung und deren Auswirkungen auf die Phosphor-Rückgewinnung. KA Korrespondenz Abwasser, Abfall, Jahrgang 69, Heft 5, 406-414.
DOI 10.3242/kae2022.05.005

Pérez, C., Boily, J. F., Jansson, S., 2021. Acid-Induced Phosphorus Release from Hydrothermally Carbonized Sewage Sludge. Waste Biomass Valor 12, 6555–6568.
DOI 10.1007/s12649-021-01463-5

Pérez, Carla, Jean-François Boily, Nils Skoglund, Stina Jansson, and Jerker Fick. 2022. “Phosphorus release from hydrothermally carbonized digested sewage sludge using organic acids.” Waste Management 60-69.
DOI 10.1016/j.wasman.2022.07.023

Petzet, S., Peplinski, B., Cornel, P., 2012. On wet chemical phosphorus recovery from sewage sludge ash by acidic or alkaline leaching and an optimized combination of both. Water Res 46: 3769-3780.
DOI 10.1016/j.watres.2012.03.068

Quicker, P. and Weber, K., 2016. Biokohle - Herstellung, Eigenschaften und Verwendung von Biomassekarbonisaten. Springer-Verlag, Berlin

Reißmann, D., Thrän, D., Blöhse, D., Bezama, A., 2020. Hydrothermal carbonization for sludge disposal in Germany: A comparative assessment for industrial-scale scenarios in 2030. Journal of Industrial Ecology, 25: 720– 734.
DOI 10.1111/jiec.13073

Reza, M. T., Andert, J., Wirth, B., Busch, D., Pielert, J., Lynam, J., Mumme, J., 2014. Review Article: Hydrothermal Carbonization of Biomass for Energy and Crop Production. Applied Bioenergy 2014. 1:11-29.
DOI 10.2478/apbi-2014-0001

Reza, M. T., Uddin, M. H., Lynam, J. G., 2014. Hydrothermal carbonization of loblolly pine: reaction chemistry and water balance. Biomass Conv. Bioref. 4, 311–321.
DOI 10.1007/s13399-014-0115-9

Roskosch, A., Heidecke, Patric, Bannick, C., Brandt, S., Bernicke, M., Dienemann, C., Gast, M., Hofmeier, M., Kabbe, C., Schwirn, K., Vogel, I., Völker, D., Wiechmann, B., 2018. Klärschlammentsorgung in der Bundesrepublik Deutschland (sewage sludge disposal in Germany). Umweltbundesamt, Dessau-Roßlau

Saetea, P., Tippayawong, N., 2013. Recovery of Value-Added Products from Hydrothermal Carbonization of Sewage Sludge. Chemical Engineering, Volume 2013.
DOI 10.1155/2013/268947

Schnell, M., Horst, T., Quicker, P., 2020. Thermal treatment of sewage sludge in Germany: A review. Journal of Environmental Management, Volume 263, 110367.
DOI 10.1016/j.jenvman.2020.110367

Shettigondahalli, E. V., Morscheck, G., Narra, S., Nelles, M., 2020. Hydrothermal Carbonization—A Sustainable Approach to Deal with the Challenges in Sewage Sludge Management. In: Ghosh, S. (eds) Urban Mining and Sustainable Waste Management. Springer, Singapore.
DOI 10.1007/978-981-15-0532-4_29

Shettigondahalli, E. V., Narra, S., Ender, T., Antwi, E., Nelles, M., 2022. Influence of Post- and Pre-Acid Treatment during Hydrothermal Carbonization of Sewage Sludge on P-Transformation and the Characteristics of Hydrochar. Processes; 10(1):151.
DOI 10.3390/pr10010151

Shi, N., Liu, Q., He, X., Wang, G., Chen, N., Peng, J., Longlong Ma, 2019. Molecular Structure and Formation Mechanism of Hydrochar from Hydrothermal Carbonization of Carbohydrates. Energy Fuels 2019, 33, 10, 9904–9915.
DOI 10.1021/acs.energyfuels.9b02174

Statistisches Bundesamat, DESTATIS, 2023. Klärschlammentsorgung nach Bundesländern.

Usman, M., Chen, H., Chen, K., Ren, S., Clark, J. H., Fan, J., Luo, G., Zhang, S. (2019): Characterization and utilization of aqueous products from hydrothermal conversion of biomass for bio-oil and hydro-char production: a review. Green Chem., 2019,21, 1553-1572.
DOI 10.1039/C8GC03957G

vom Eyser, C., Palmu, K., Schmidt, T.C., Tuerk, J., 2015. Pharmaceutical load in sewage sludge and biochar produced by hydrothermal carbonization. Sci. Total Environ. 537, 180–186.
DOI 10.1016/j.scitotenv.2015.08.021

Wang, H., Yang, Z., Li, X., 2020. Distribution and transformation behaviors of heavy metals and phosphorus during hydrothermal carbonization of sewage sludge. Environ Sci Pollut Res 27, 17109–17122.
DOI 10.1007/s11356-020-08098-4

Wang, L., Chang, Y., Liu, Q., 2019A. Fate and distribution of nutrients and heavy metals during hydrothermal carbonization of sewage sludge with implication to land application, Journal of Cleaner Production, Volume 225, 2019, 972-983.
DOI 10.1016/j.jclepro.2019.03.347

Wang, L., Chang, Y., Li, A., 2019B. Hydrothermal carbonization for energy-efficient processing of sewage sludge: A review. Renewable and Sustainable Energy Reviews, Volume 108, 2019, 423-440.
DOI 10.1016/j.rser.2019.04.011

Wilson, C.-A., Novak, J.-T., 2009. Hydrolysis of macromolecular components of primary and secondary wastewater sludge by thermal hydrolytic pretreatment, Water Research, Volume 43, Issue 18, 2009, 4489-4498.
DOI 10.1016/j.watres.2009.07.022

Wirth, B., Reza, M. T., Mumme, J., 2015. Influence of digestion temperature and organic loading rate on the continuous anaerobic treatment of process liquor from hydrothermal carbonization of sewage sludge. Bioresource Technology, Volume 198, 2015, Pages 215-222.
DOI 10.1016/j.biortech.2015.09.022

Woriescheck, T., 2019. Charakterisierung, Aufreinigung und Wertstoffgewinnung von Prozesswasser der Hydrothermalen Carbonisierung. (Doctoral dissertation). University of Oldenburg, Germany: Oldenburg. Retrieved from,contains,49GBVUOB_ALMA51338789630003501

Xu, Z.-X., Ma, X.-Q., Zhou, J., Duan, P.-G., Ahmad, A., Luque, R., 2022. The influence of key reactions during hydrothermal carbonization of sewage sludge on aqueous phase properties: A review. Journal of Analytical and Applied Pyrolysis, Volume 167, 2022, 105678.
DOI 10.1016/j.jaap.2022.105678

Zhang, H.-Y., Ju, Y.-Y., Fan, Z.-M., Wang, B., 2010. Acid buffer capacity of sewage sludge barrier for immobilization of heavy metals. Huan Jing Ke Xue. 2010 Dec;31(12):2956-64. Chinese. PMID: 21360886