**Kazimierz Gaj**

Faculty of Environmental Engineering, Wroclaw University of Science and Technology, 50-370 Wrocław, Poland; kazimierz.gaj@pwr.edu.pl

Received: 17 April 2020; Accepted: 13 May 2020; Published: 20 May 2020

**Abstract:** Siloxanes are among the most technologically troublesome trace compounds present in biogas. As a result of their combustion, hard-to-remove sediments are formed, blocking biogas energy processing devices and reducing the e fficiency of biogas plants. The purpose of this study was to help investors and designers to choose the optimal technology for the adsorptive removal of volatile methylsiloxanes (VMSs) from biogas and to identify adsorbents worth further development. This paper critically reviews and discusses the state-of-the-art technologies for the adsorption removal of siloxanes from biogas, indicating potentially beneficial directions in their development and deficiencies in the state of knowledge. The origin of VMSs in biogas, their selected physicochemical properties, technological problems that they can cause and their typical versus limit concentrations in biogases are presented. Both the already implemented methods of adsorptive VMSs removal from landfill and sewage gases and the ones being under development are verified and systematized. The parameters and e ffectiveness of adsorption processes are discussed, and individual adsorbents are compared. Possible ways of regenerating spent adsorbents are evaluated and prospects for their application are assessed. Finally, zeolite-based adsorbents—which can also be used for biogas desulfurization—and adsorbents based on polymer resins, as being particularly active against VMSs and most amenable to multiple regeneration, are identified.

**Keywords:** biogas treatment; volatile methylsiloxanes; siloxane concentrations; adsorbents; regeneration
