Anaerobic digestion at high-pH and alkalinity for biomethane production
Insights into methane yield, biomethane purity, and process performance
Beatriz C. Diniz (TU Delft - BT/Environmental Biotechnology)
P. Wilfert (TU Delft - BT/Environmental Biotechnology, Technische Hochschule Lübeck)
Dimitry Y. Sorokin (Russian Academy of Sciences, TU Delft - BT/Environmental Biotechnology)
Mark M.C. van Loosdrecht (TU Delft - BT/Environmental Biotechnology)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
The role of high-pH conditions in anaerobic digestion (AD) has traditionally been confined to it's use in pre-treatment processes. However, operating AD at elevated pH and alkalinity offers significant advantages, including in-situ upgrading of biogas to biomethane. This study examines the potential and scalability of AD under these conditions (pH ∼ 9.3; alkalinity ∼ 0.5 eq/L). The substrate used was the alkaline waste generated from the extraction of extracellular polymeric substances (EPS) from aerobic granular sludge (AGS), and the inoculum used was a haloalkaliphile microbial community from soda lake sediments. To evaluate the system’s performance, the organic loading rate (OLR) was incrementally increased. The highest methane production obtained was 8.4 ± 0.1 mL/day/gVSadded at a hydraulic retention time (HRT) of 15 days and an OLR of 1 kgVS/day/m3. At this loading rate, methanogenesis became the rate limiting conversion. The maximum volatile solids conversion was 48.1 ± 1.1 %. Throughout the reactor operation, methane purity in the biogas consistently exceeded 90 % peaking at 96.0 ± 0.2 %, showcasing the potential for in-situ biogas purification under these conditions. In addition, no ammonia inhibition was observed, even with free-ammonia (NH3) concentrations reaching up to 14 mM. This study underscores the potential of high-pH anaerobic digestion as a sustainable method for both waste treatment and energy recovery.
help_outline