Effect of surfactant addition on the biofiltration of siloxane-contaminated gas streams

Abstract

Biogas contains low levels of volatile methyl siloxanes (VMS), which are responsible for severe damage to turbines or internal combustion engines during energy recovery. In this study, we investigated the removal of the linear octamethyltrisiloxane (L3) and cyclic octamethylcyclotetrasiloxane (D4) from gas by using two biofilters (BFs) filled with either woodchips and compost (WC) or perlite (PER). To overcome the mass transfer limitation, the addition of a synthetic (Tween 80) and a biological (Quillaja saponin, QS) surfactant on the removal of VMS in both BFs was studied. Tween 80 (added at × 1 critical micelle concentration, CMC) and QS (also at × 1 CMC) enhanced VMS removal in both BFs. Specifically, the performance of both BFs increased from an average VMS elimination capacity (EC) of 0.07 ± 0.04 g VMS m−3 h−1 to 0.24 ± 0.08 g VMS m−3 h−1 (Tween 80) and 0.43 ± 0.02 g VMS m−3 h−1 (QS). However, higher concentrations of Tween 80 ( × 3 CMC) did not further improve VMS removal. The WC BF exhibited a higher maximum EC of 0.63 g VMS m−3 h−1 (0.37 g D4 m−3 h−1 and 0.26 g L3 m−3 h−1), with a VMS RE of 28.4 ± 2.0% (D4 RE = 30.4% and L3 RE = 26.5%). The PER BF obtained a maximum EC of 0.52 g VMS m−3 h−1 (0.28 g D4 m−3 h−1 and 0.23 g L3 m−3 h−1), along with a VMS RE of 32.0 ± 0.8% (D4 RE = 31.2% and L3 RE = 32.8%). The most abundant genera in the WC BF were Mycobacterium (7.5–1.8%), Rhodococcus (1.1–7.2%), and Planctomicrobium (5.1–2.9%). However, given the high microbial diversity present in WC BF and the complex structure of VMS, their removal was most likely due to the joint activity of several microorganisms with VMS-degrading capacity, such as Bacillus (0.58–0.39%), Pseudomonas (0.07–0.04%), Dokdonella (0.50–0.10%), Microbacterium (0.5%), Novosphingobium (0.02%), Gordonia (0.5–0.1%), and Sphingopyxis (0.07%).