| With the rapid development of urbanization and industrialization, the environmental pollution is becoming more and more serious. Among them, malodorous gaseous pollutants arouses wide public concern. Hydrogen sulfide (H2S) is one of the representative odorous compounds. For the sake of reducing the cost of packing material and waste reutilization, extensive studies have been carried out to understand the role of mature compost as packing material for H2S removal. However, most studies focused on the global removal efficiency including physical, chemical, and biodegradation removal of H2S. Less effort has been made to address the important role of adsorption and absorption of the compost in the H2S treatment. In addition, in order to increase the stability of the compost packing media, wood chips, perlite or other agents have always been mixed with compost. Studies elucidating the role of compost as a sole packing media are few. Therefore, this study was conducted in an attempt to understand the mechanism of H2S removal by using only pig manure compost as the packing material. The following conclusions can be drawn:(1) Without inoculation, or even been sterilized, pig manure compost maintained almost 100% removal efficiency for H2S, when running time was less than 200 h, and the inlet concentration was lower than 1656 mg/m3. In addition, fluctuation in inlet H2S concentration had almost no effect the removal efficiency. Results showed that water content, empty bed residence time (EBRT), and H2S loading influenced the removal efficiency. Increase in both water content within rage of 1.5-44% and EBRT lead to higher efficiency. On the other hand, removal efficiency droped when inlet H2S loading got higher. However, high H2S loading resulted in high elimination capcity up to 846 (g H2S)/(m3 compost)/h.(2) Pig manure compost at different height contributes differently to the H2S removal. More than 50% of H2S were removed by the compost located below the one quarter of the whole packing height. Packing media near the bottom eliminated more H2S.In addition, pressure drop during the experiment run ranged from 220-306Pa/m, which is higher than those reported in the literature. Mixing with perlite or other agents to increase the porosity of packing media and lowering the pressure drop is necessary.(3) Results revealed that removal mechanism of H2S by pig manure compost included absorption, adsorption and catalyzed oxidation. Removal can be described with first order reaction kinetics.Removal of H2S leaded to the formation of element sulfur and SO42-. BET analysis showed that after retaining H2S, total porosity reduced by 5.04×10-3 cm3/g and specific area decreased from 2.48 m2/g to 0.85 m2/g. The reason is probably that some pores were blocked by the element sulfur. Decrease in porosity and specific area gave rise to the observed efficiency reduction as the running time elapsed. In addition, formation of SO42- lead to the decrease in pH value, which in turn inhibited the H2S removal. Analysis indicated that removal efficiency began to decrease after the total Sulfur reached 3.4%. When the maxium elimination capacity was achieved, total sulfur content was 91(g S)/(m3 compost). Upon this point, unless appropriate treatment was done for the packing compost, removal efficiency would approach immediately zero. |
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