Fundamental Studies On Siloxanes And Hydrogen Sulfide Removal From Energy Gases Using Biological Process

Exploitation of energy gases such as natural gas or biogas is clearly limited by thepresence of siloxanes and hydrogen sulfide. With the process of removingoctamethylcyclotetrasiloxane and hydrogen sulfide from the simulated gas in anaerobic biotrickling filter (BTF) as the target, the operating parameters, the gas-liquidinterfacial mass transfer characteristics and the degradation products wereinvestigated using16S rDNA sequencing, TEM, GC-MS, HPLC-MS, ATR-FTIR,NDIR and SEM-EDS. The main findings are as follows:In the activated sludge-inoculated BTF, the removal efficiency (RE) of D4wasnearly independent of the liquid recirculation rate when it was in the range of1.1m·h-1~4.5m·h-1. The effect of gas empty bed residence time (EBRT) on D4removalwas studied by feeding50mg·m-3D4to the BTF while applying variable gas flowrates. As a result, the removal of D4followed a rising trend, reaching53%at anEBRT of17.7min. Since the accumulation of D4in liquid phase was not detected byGC-MS, the BTF was mass-transfer limited. Additionally, based on the D4profilemeasurements along the packing height, D4was consumed primarily near the inlet ofthe BTF.To improve the gas-liquid transfer of D4, a cationic surfactant cetyl trimethylammonium bromide (CTAB) and a nonionic surfactant fatty alcohol-polyoxyethyleneether (AEO-7) were introduced into the recirculating medium of the BTF. However,the introduction of CTAB resulted in a decrease in the RE of D4, while theintroduction of AEO-7led to a transient increase in the RE.A strain of Pseudomonas aeruginosa S240, which is able to degrade D4effectively, was isolated from the activated sludge-inoculated BTF. At a inlet D4concentration of50mg·m-3and an EBRT of13.2min, the RE value could reach60%in the strain S240-inoculated BTF. Rha Rha C10, Rha Rha C8C8and Rha C12:1C10,three kinds of rhamnolipid produced by strain S240grown on D4, were identified inthe liquid phase of the BTF, and they were found to be the main factor of improvingD4removal. Moreover, dimethylsilanediol, methanol, silicic acid and carbon dioxide,as the biodegradation products of D4, were determined. To our best knowledge, it isthe first time to report the existence of methanol in the D4degradation products. At a inlet H2S concentration of around7500ppm and an EBRT of88s, the REvalue could reach above99%in the BTF where Acidithiobacillus ferrooxidans wasthe predominant genus in the mixed population. Besides, the BTF became kineticallylimited when increasing the inlet concentration at a constant EBRT, but gotmass-transfer limited when reducing the EBRT at a constant inlet concentration.Finally, when the H2S supply was shut down for48h, a large number of jarosite wasgenerated in the BTF, which would cause a obvious decrease in RE of H2S.Nonetheless, the generation of jarosite could be inhibitted via medium renewals.