Anaerobic digestion of algae harvested from an algal turf scrubber at the Port of Baltimore

Danielle Delp

University of Maryland

Co-Authors: Andrea Yaberry, Peter May, Patrick Kangas, Freddy Witarsa, and Stephanie Lansing

Algal turf scrubber (ATS) technology allows for the rapid cultivation of algal biomass while removing excess nutrients from eutrophic waters. Research at the Port of Baltimore in Maryland explored the potential for ATS algae to act as a feedstock for biomethane production via anaerobic digestion (AD) in three digester units over three growing seasons between July 2017 and October 2019. Two 3 m3 digesters (D1 and D2) were operated up in parallel, with the 1 m3 digester (D3) connected in series to D2 to extend the hydraulic retention time (HRT) of the D2-D3 system. Biogas volume and composition were measured weekly in the field with a Landtec 3000 Biogas meter measuring CH4, H2S, CO2 and O2. Influent and effluent samples were collected weekly and tested for temperature, pH, total Kjeldahl nitrogen (TKN), total phosphorus (TP), and total and volatile solids (TS and VS). Results from 2018 and 2019 will be presented.

Over the 13-week 2018 harvest period, D1 and D2-D3 systems were fed 3.5 m3 of algae and produced 1.8 and 2.5 m3 of biogas, respectively. The average CH4 concentration in the biogas in D1, D2, and D3 was 73.0 ± 1.6, 68.9 ± 3.4, and 69.2 ± 2.8%, respectively. During the 2019 growing season, improved ATS function resulted in 6.2 m3 of algae to be fed to the system over 18 weeks, resulting in 2.8 and 8.8 m3 of biogas produced in D1 and D2-D3, respectively. Average CH4 concentration in D1, D2, and D3 biogas during the experimental period was 69.7 ± 3.0, 65.9 ± 4.2, and 63.6 ± 6.6%, respectively. Relatively low average H2S content was observed during both experimental periods (<5 ppm in 2018 and <900 ppm in 2019) which reduces the likelihood of corrosion in electricity generation or fuel cells that use algae-derived biogas to generate electricity.

This is the first system to combine these technologies for energy production at-scale. The results presented will show the potential for combined renewable energy production with remediation of eutrophic surface water.

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