Author:   Berrin Tansel, Florida International University, Department of Civil & Environmental Engineering

Co-Author:Sharon C. Surita,Florida International University, Department of Civil & Environmental Engineering

In recent years, siloxane use in consumer products such as fabrics, paper, concrete, wood, and adhesive surfaces, has increased due to their antimicrobial characteristics and superior water repellent characteristics.  Siloxanes have been detected in biogas produced at municipal solid waste (MSW) landfills and wastewater treatments plants (WWTP) and are transported with wind currents. These compounds contain silicon atoms attached to organics and convert into silicates (SiO2 or SiO3) during combustion. Silicon dioxide formed from the siloxanes can range from 5 nm to about 100 nm in diameter depending on the combustion temperature and particle clustering characteristics.  These nanoparticles are described as fibrous dusts and are identified as potential carcinogenic, mutagenic, asthmogenic or reproductive (CMAR) toxics.  Exposure to Si-based particles and the potential effects in humans has been analyzed in relation to particle sizes, release rates and availability in the atmosphere.  Additionally partitioning into different environmental compartments has been analyzed to predict an exposure hazards index.  Some waste to energy (WTE) facilities have installed gas treatment processes (e.g., carbon adsorption, silica gel adsorption) to reduce siloxane deposit formation in engine parts. However, the addition of gas treatment systems increases the energy recovery costs at WTE facilities operated with LFG. Data acquired from monitoring at a local landfill and wastewater treatment plant has demonstrated the inefficiency of scrubbers to remove siloxane compounds prior to cogeneration.

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