Full-scale digester micro-aeration studies to improve biogas quality: PRESENTATION ONLY
Kraakman, B.1,2, Diaz, I.2, Muñoz, R.2, 1 Jacobs, UK, 2Institute of Sustainable Processes, University of Valladolid, Spain
(free)
Biogas generated from anaerobic digestion typically requires gas conditioning before it is used to generate energy. Elevated concentrations of hydrogen sulfide (H2S) in the biogas is often a limitation for downstream processing of biogas. Full-scale tests using micro-aeration technology were undertaken and showed that this new process-integrated technology has potential using minimum plant upgrading while contributing to the sustainability and economic efficiency of the energy recovery process of waste sludge digestion at wastewater treatment plants (WWTPs).
The main objective of this presentation is to share information and experiences about micro-aeration as an effective digester biogas conditioning technology. The presentation will include bench-scale research and full-scale testing data and tries to overcome the lack of full-scale experience with micro-aeration in digesters at WWTPs.
Micro-aeration technology was tested in full-scale digesters at different WWTPs. A comparison between the different types of digesters (i.e. mechanical mixing and gas mixing) are made to better understand in how micro-aeration can be best applied. Figure 1 illustrates an example how micro-aeration reduces the H2S reduction in the produced biogas from 5,000 ppmv to less than 1,000 ppmv when the micro-aeration was stopped.
Figure 1: H2S in the biogas during the initial phase 1 of a micro-aeration test.
The presence of small amounts of oxygen in the anaerobic digestion process in the full-scale test did not impact neither on organic matter removal nor on the biomethane productivity when the amount of air injected is limited. In fact, these full-scale tests confirms that, besides efficiently desulfurizing biogas, micro-aeration can potentially improve organic matter degradation during municipal sludge digestion. The volatile solids content dropped in the above full-scale example from about 66.6% without to about 63.6% with the micro-aeration.
