Reducing greenhouse gas emissions and improving sludge dewaterability with vacuum degassing of digested sludge

Cadavid, G.1, Dittmann, M.1, O’Brien, L.2, 1ELIQUO WATER GROUP GmbH, 2ELIQUO HYDROK LTD


Methane emissions from sludge treatment make up 75% of the diffuse CO2-equivalent emissions from
wastewater treatment plants (Gärtner 2017). A vacuum degassing technology developed by ELIQUO
uses a vacuum pump to extract methane from the digested sludge reducing greenhouse gas
emissions while providing additional gas yield to the CHP. This technology has been demonstrated on
a full scale, in combination with thermal pressure hydrolysis and phosphor reduction by means of
struvite precipitation. The effect of vacuum degassing is equivalent to 3 kg of avoided CO2-
equivalents per cubic metre of sludge or a 25% reduction of the total diffuse CO2-equivalent
emissions of the treatment plant. Furthermore, vacuum degassing can provide up to 3%-points
improvement in dewatering, which can reduce total sludge disposal by up to 15%. Vacuum degassing
can be installed as a stand-alone system without disruption of existing treatment processes. This
paper details the data and findings from the full-scale implementation.

Biogas yield, biosolids treatment, carbon footprint, methane emissions, sludge dewatering, struvite
precipitation, thermal hydrolysis, vacuum degassing

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