Hydrochar from dairy sludge as phosphorus fertiliser affects greenhouse gas emissions and maize yield

ABSTRACT

Dairy processing sludge is a phosphorus (P) rich waste with a high potential to replace mineral phosphorus fertiliser in crop production, with possible enhancement of greenhouse gas emissions to the environment. Hydrothermal carbonisation is a technology that transforms the sludge into a hydrochar. The objective of this study is examining P availability of two hydrochars produced from Danish and Irish dairy sludge and their influence on greenhouse gas emissions and maize yields. The trial assessed (i) Danish dairy sludge; (ii) hydrochar derived from Danish sludge; (iii) hydrochar made from Irish dairy sludge; (iv) mineral phosphorus fertiliser; and (v) control. Emissions of nitrous oxide and carbon dioxide, soil pH, mineral nitrogen contents and crop yields were measured. Treatment with Danish dairy sludge had significantly higher cumulative nitrous oxide emissions while the emissions from both hydrochars were not significantly different compared to mineral phosphorous feriliser. Statistical modelling showed that temperature, soil nitrate content, interactions both between temperature and precipitation, and between soil moisture and precipitation were drivers for nitrous oxide emissions. There was no difference in emissions among all treatments when scaled for yield. Hydrochar may alleviate the enhanced nitrous oxide emissions in soil without constraining P availability and maize crop yields.

GRAPHICAL ABSTRACT

KEYWORDS:

• Bio-based fertiliser
• Dairy manures
• Environment
• Hydrothermal carbonisation
• Soil
• STRUBIAS

Acknowledgements

This project has received funding from the European Union’s Horizon 2020 Marie Skłodowska-Curie Actions (MSCA) Innovative Training Networks (ITN) under the agreement REFLOW No 814258. We would also like to acknowledge Jens Bonderup Kjeldsen and Bodil Stensgaard for their help in the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Yihuai Hu

Yihuai Hu was a PhD student during this study, and he is now working at Biogas Institute of Ministry of Agriculture and Rural Affairs, China.

Arezoo Taghizadeh-Toosi

Arezoo Taghizadeh-Toosi is a research scientist working at Danish Technological Institute and UK Centre for Ecology & Hydrology. She is a corresponding author for this article.

Khagendra R. Baral

Khagendra R. Baral is senior scientific officer at Agri-Food and Bioscience Institute, Ireland.

Aidan M. Smith

Aidan M. Smith is an assistent professor at Aarhus University, Denmark.

Nidal Khalaf

Nidal Khalaf is a researcher at University of Limerick, Ireland.

Sven G. Sommer

Sven G. Sommer is a professor at Aarhus University, Denmark.