Evaluation of a Full-Scale Water-Based Scrubber for Removing Siloxanes from Digester Gas: A Case Study

Siloxanes are becoming more prominent in digester gas at water resource recovery facilities because of their wide use in personal care products. This study evaluates a full-scale water-based scrubber operating in a water resource recovery facility (Miami, FL). The digester gas is used for energy generation due to its high methane content. During energy generation, siloxanes are converted to silicates and Silicon Dioxide (SiO2), which leave deposits on engine components. Trimethylsilanol (TMSOH), Octamethyltrisiloxane (L3), Hexamethylcyclotrisiloxane (D3), Octamethylcyclotetrasiloxane (D4), Decamethylcyclopentasiloxane (D5), and Dodecamethylcyclohexasiloxane (D6) were detected in the digester gas. D4 and D5 were present at the highest concentrations, 5000 and 1800 μg/ m3, respectively. Sampling results have indicated that scrubbers employed for hydrogen sulfide (H2S) removal at the facility do not provide effective removal of siloxanes due to their high Henry's Constant. Post scrubber treatment is needed to remove siloxanes from the digester gas prior to combustion.