Siloxanes in biogases from landfills and wastewater digesters

Abstract

Volatile methylsiloxanes and linear polydimethylsiloxanes (siloxanes), generated as components of biogases from digesters at wastewater treatment plants and solid waste landfills, have been identified as potentially causing significant operational problems. The problems are demonstrated as being an issue of “sand in the transmission” and are the reason for the changing of engine warrantees. Examples of monitored concentrations of siloxanes at a series of facilities are described, demonstrating degrees of variability both spatially and temporally, for different biogas sources. Wastewater digesters are shown to be generally producing biogases with higher siloxane concentrations than landfills. With a trend toward some landfills being operated as bioreactors, where the temperatures in the refuse are elevated to levels comparable to those within wastewater treatment digesters, there is potential that landfill-derived biogases may result in increased concentrations of siloxanes and hence more operating problems.