Water engineering firm Eliquo Hydrok presented at the European Biosolids & Organic Resources Conference and Exhibition held at the Royal Armouries, Leeds in November 2018. The paper looked at degassing for digested sludge using the firm’s EloVac® system and thermal hydrolysis process with another proprietary technology called “LysoTherm”.
As the firm explained, CH4 emissions from sludge treatment make up 75% of the diffuse CO2-equivalent emissions from wastewater treatment plants. While CH4 is a powerful greenhouse gas (one CH4 corresponds to 28 CO2 equivalents), CH4 is also a highly energetic gas with a calorific value of 10 kWh/m³. As a unique technology for vacuum degassing of digested sludge, EloVac® takes advantage of these two facts – it uses a vacuum pump to extract methane from the digested sludge, and in doing so, it not only withdraws soluble gas from the digested sludge, but also very small gas bubbles attached to particles. This is a major contribution to reducing greenhouse gas emissions, while providing additional gas yield to the CHP, said Eliquo.
In addition to the environmental benefits, EloVac® can also improve the dewaterability of digested sludge by up to 3%-points.
In Lingen in Northwest Germany, a 195,000 P.E. WwTP, where a full scale EloVac® unit is operating the following results have been achieved:
• At 230 milibar, 340 L of biogas per m³ of sludge can be withdrawn, resulting in ca.150 tons of CO2-emissions avoided per year or 25% of the CO2 – equivalent emissions of the treatment plant.
• Due to better dewatering, reduction in the sludge hauling disposal by up to 15% solely by EloVac® (based on TR(A) measurements).
• The overall plant optimisation project in Lingen, including the implementation of other Eliquo Technologies: LysoTherm® (Unique Thermal Hydrolysis Technology with no stem and no chemicals) and EloPhos® (controlled struvite precipitation) together with EloVac®, have resulted in 484,000 €/year in operational savings and 400 tons/year of CO2 equivalent emissions avoided. The avoided emissions are approximately equivalent to 8,500-car kilometres/day – the same distance as driving from the U.K. to Japan every day!
Eliquo is currently conducting lab tests to identify the benefits U.K. water utilities can expect with EloVac®, dependent on their specific sludge characteristics.
