Adsorption of Hydrogen Sulphide using zeolite ZSM–5 for the enhancement of fermentative biohydrogen production

Biohydrogen production from mixed fruit waste (MFW) is a renewable energy source. However, the presence of highly toxic and corrosive hydrogen sulphide (H2S) might reduce performance and limit energy conversion equipment use. Adsorbents including zeolites, biochar, and activated carbons have become popular for treating harmful gases like H2S. Thus, the research examined the feasibility of employing ZSM-5 zeolite for H2S adsorption as an activating agent to improve biohydrogen quality from thermophilic condition. A suspension rich in carbohydrate from MFW was used at initial concentration 5 g/L during the fermentation process was conducted in a thermophilic anaerobic closed bioreactor (TACB) at an initial pH 6 and temperature 60 ℃. Hydrogen-producing bacteria via the butyric acid fermentation route were the most prevalent microbes in biohydrogen generation. Volumetric biohydrogen yield and substrate degradation efficiency was 22511.60 mL and 85% per total carbohydrate, respectively obtained in the experiments performed. The biogas that was produced had undergone adsorption process on zeolite ZSM-5. The effect of dosage of adsorbents and reaction temperature on the hydrogen yield and H2S removal investigated. The hydrogen yield after adsorption process increased from 89% to 92.78%. The optimum dosage and reaction temperature for H2S adsorption were 0.8 g (0.00889 mg/g) and 25 ℃ (0.00890 mg/g), respectively. The zeolite was subjected to consecutive regeneration and adsorption cycle where H2S adsorption capacities of 0.00890 mg/g were maintained for 3 cycles demonstrating reusability and stability of the sorbents. However, the adsorption capacity starts reducing at the fourth cycle. The H2S removal on zeolite ZSM-5 was the best represented by Avrami kinetics model showing that H2S were adsorbed via multiple adsorption pathways with multilayer adsorption on heterogenous surface. The adsorption is physical adsorption, exothermic, increasingly random, and non-spontaneous. Intra-particle diffusions were found to critically control the rate of adsorption. Higher H2S adsorption capacity and regenerability shown by fibrous zeolite in this this study confirmed its applicability as an alternative sorbent in enhance biohydrogen quality under thermophilic conditions.