Pilot Study of Siloxanes Removal from Digester Biogas through Various Adsorbents

In order to evaluate some innovative siloxane adsorbent materials and compare their siloxane removal capacity with regular granular activated carbon (GAC), an eight months pilot study was conducted at the Hampton Roads Sanitation District (HRSD) Nansemond Treatment Plant as a collaborative research effort sponsored by R + i Alliance and the Water Environment Research Foundation.In this study, five siloxane adsorbents including silica gels from two manufacturers, polymorphous graphite (PMG), DOWEX V503, and a vapor phase GAC were tested in a biogas conditioning pilot. Five sets of testing were conducted. In each test, the pilot operation conditions were closely monitored and recorded. Biogas samples were collected at process points regularly for siloxane and H2S analysis. For each test, the total treated biogas flow was recorded, the siloxane adsorbed by adsorbents and their siloxane removal capacities (siloxane removed/unit weight of adsorbent) were calculated. The impact of process conditions such as compression/refrigeration, and the impact of hydrogen sulfide in the biogas were also evaluated.The results of this pilot study provided some reliable information of these adsorbents in their siloxane removal capabilities. The pilot study also provides useful information for the design of siloxane removal process including adsorbent selection and reactor sizing.