Proceedings

Eliminating residual methane from digested sludge is key to achieving a climate neutral STW: PRESENTATION ONLY

Maria Dittmann, Eliquo Stulz GmbH

(free)

Wastewater is the fifth largest source of anthropogenic CH4 emissions – accounting for 523 Mg CO2e emissions per year. This corresponds to 9 % of the total CH4 emissions worldwide [2]. According to different studies, 79 to 90% of those CH4 emissions are related to anaerobic digestion [1, 3]. These emissions could have a larger negative impact on the CO2 footprint than the positive impact from the avoided carbon dioxide emissions by using the resulting biogas for energy generation. This would mean anaerobic digestion actually downgrades the carbon footprint of STWs.

However, there are relatively easy ways to avoid direct methane emissions from anaerobic digestion. Vacuum degassing of digested sludge can contribute significantly to avoiding those GHG emissions and therefore eliminates the negative impact from anaerobic digestion. The vacuumed gas is not diluted by air and can, therefore, be utilized for energy generation. A full-scale operating plant with vacuum degassing post digestion showed an energy neutral operation of the unit and a reduction in the total carbon footprint of the plant by 25%. Additionally, vacuum degassing of digested sludge has further operational benefits, such as improvement in dewaterability, polymer consumption and increased density of digested sludge.

[1] Tolkou, A., Zouboulis, A. Effect of climate change in WWTPs with a focus on MBR infrastructure, Desalination and water treatment, May 2015

[2] Zouboulis, A., Tolkou, A. Effect of Climate Change in Wastewater Treatment Plants: Reviewing the Problems and Solutions, Springer International Publishing Switzerland 2015

[3] Gärtner, A., Hirschberger, R. und Becker, A. Diffuse biogene Emissionen auf Kläranlagen [Diffuse biogenic emissions from WWTPs]. [Hrsg.] DWA. Korrespondenz Abwasser. 11 2017, S. 985 – 993.

Authors:

Neil Willoughby ELIQUO HYDROK Ltd T +44 (0) 1726 862000 M +44 (0) 7387 080105

Maria Dittmann ELIQUO STULZ GmbH M +49 151 58954415 T +49 751 359785-14

Lewis O’Brien ELIQUO HYDROK Ltd T +44 (0)1726 861900 M +44 (0)7854 580022

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