Influence of free ammonia extraction in methane production from human urine

ABSTRACT

Human urine has a high chemical oxygen demand (COD) content which makes anaerobic treatments potentially appropriate for the management of yellow waters, allowing for energy recovery. However, its high N content makes this treatment challenging. The present work studied the viability of performing an anaerobic digestion process for COD valorization on a real (not synthetic) urine stream at laboratory scale. To deal with nitrogen inhibition, two different ammonia extraction systems were proposed and tested. With them, a proper evolution of acidogenesis and methanogenesis was observed. Nitrogen was recovered in the form of ammonium sulphate, which could be used for agriculture, in two different ways: ammonia extraction from the urine stream before feeding the reactor and in situ extraction in the reactor. The first method, which proved to be a better strategy consisted in a desorption process (NaOH addition, air bubbling and acid (H₂SO₄) absorption column, HCl for final pH adjustment) whereas the in situ extraction in the reactor consisted of an acid (H₂SO₄) absorption column installed in the biogas recycling line of both reactors. Stable methane production over 220 mL/g COD was achieved and methane content in the biogas was stable around 71%.

GRAPHICAL ABSTRACT

KEYWORDS:

• Anaerobic digestion
• free ammonia inhibition
• nitrogen recovery
• urine
• yellow water

Acknowledgements

This research project has been supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, project CTM2017-86751-C2), whose support is gratefully acknowledged.

Disclosure statement

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

Competing interests

Authors declare they have no financial or non-financial interests directly or indirectly related to the work submitted for publication.

Author contributions

J. Serralta, J. Ferrer and A. Seco contributed to the study conception and design. Material preparation, data collection and analysis were performed by S. Greses, E. Jiménez, and J. Claros. A. Ruiz-Martinez performed data analysis and wrote the first draft of the manuscript. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

This research work was possible thanks to the project IISIS IPT-20111023, an INNPRONTA 2011 project granted to FCC Aqualia, partially funded by the Centre for Industrial Technological Development (CDTI) and supported by the Spanish Ministry of Economy and Competitiveness.