Abstract
Acidic biotrickling filters (BTF) can be used for simultaneous removal of hydrogen sulfide (H2S) and siloxane from biogas. In this study, the performance of a BTF under different acidic pH conditions was investigated. The removal profile of H2S showed that 90% of H2S removal was achieved during the first 0.4 m of BTF height with down-flow biogas. Decamethylcyclopentasiloxane (D5) removal decreased from 34.5% to 15.6% when the pH increased from 0.88 to 3.98. Furthermore, the high partition coefficient of D5 obtained in under higher pH condition was attributed to the higher total ionic strength resulting from the addition of sodium hydroxide solution and mineral medium. The linear increase in D5 removal with the mass transfer coefficient (kL) indicated that the acidic recycling liquid accelerated the mass transfer of D5 in the BTF. Therefore, the lower partition coefficient and higher kL under acidic pH conditions lead to the efficient removal of D5. However, the highly acidic pH 0.9 blocked mass transfer of H2S and O2 gases to the recycling liquid. Low sulfur oxidation activity and low Acidithiobacillus sp. content also deteriorated the biodegradation of H2S. Operating the BTF at pH 1.2 was optimal for simultaneously removing H2S and siloxane.
Highlights
The ECD5 decreased from 316 mg/(m3·h) to 246 mg/(m3·h) as the pH increased from 0.9 to 1.2 at the LRD5 of 1,200 mg/(m3·h) and decreased from 324 mg/(m3·h) to 222 mg/(m3·h) as the pH increased from 2.0 to 4.0 at the LRD5 of 1,700 mg/(m3·h)
Compared with the pH-neutral biotrickling filters (BTF) (Montebello et al ; Tu et al ), our results indicate that an acidic BTF led to specialization of the bacterial community and the prevalence of Acidithiobacillus sp
In the pH range of 1.66â2.90, the kL decreased slowly from 0.060 m/h to 0.035 m/h, and decreased to 0.029 m/h when at pH 5.64. These results indicate that the mass transfer of D5 from the headspace gas to the liquid at the bottom of the flask was accelerated by the acidic recycling liquids, especially under extremely acidic pH conditions
Summary
Biogas from anaerobic digestion of organic compounds is a promising renewable biofuel that can be used to produce heat, steam, electricity, fuel, or for gas-grid injection Apart from methane (CH4) and carbon dioxide (CO2), biogas contains trace impurities, such as hydrogen sulfide (H2S) (50â10,000 ppmv) (Pipatmanomai et al ) and siloxanes (10â400 mg/m3) (Dewil et al ; Oshita et al ; Raich-Montiu et al ; Zhang et al ). H2S is limited to [1â250] ppmv (Sun et al ; Khan et al ) and siloxanes to 0.1â30 mg/m3 (Dewil et al ; Ryckebosch et al ; Arespacochaga et al b; Hepburn et al ; Tansel & Surita )
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