Abstract

The removal of dissolved sulfides in water and wastewater by nanoscale zero-valent iron (nZVI) was examined in the study. Both laboratory batch studies and a pilot test in a 50,000-pig farm were conducted. Laboratory studies indicated that the sulfide removal with nZVI was a function of pH where an increase in pH decreased removal rates. The pH effect on the sulfide removal with nZVI is attributed to the formation of FeS through the precipitation of Fe(II) and sulfide. The saturated adsorption capacities determined by the Langmuir model were 821.2, 486.3, and 359.7 mg/g at pH values 4, 7, and 12, respectively, for nZVI, largely higher than conventional adsorbents such as activated carbon and impregnated activated carbon. The surface characterization of sulfide-laden nZVI using XPS and TGA indicated the formation of iron sulfide, disulfide, and polysulfide that may account for the high adsorption capacity of nZVI towards sulfide. The pilot study showed the effectiveness of nZVI for sulfide removal; however, the adsorption capacity is almost 50 times less than that determined in the laboratory studies during the testing period of 30 d. The complexity of digested wastewater constituents may limit the effectiveness of nZVI. Microbial analysis suggested that the impact of nZVI on the change of microbial species distribution was relatively noticeable after the addition of nZVI.

Highlights

  • Anaerobic digestion of piggery wastewater is capable of producing methane-rich biogas and minimizing the environmental impact caused by the wastewater

  • 95% of initial sulfide concentration was removed at pH 4

  • The adsorption capacity is almost 50 times less than that determined in the laboratory studies at pH 7

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Summary

Introduction

Anaerobic digestion of piggery wastewater is capable of producing methane-rich biogas and minimizing the environmental impact caused by the wastewater. The methanerich biogas is a renewable energy resource that can be used to generate electricity. The Kyoto Protocol has explicitly defined methane as one of the six key greenhouse gases where the global warming potential of methane is 25 times higher than that of carbon dioxide [1]. The use of methane for electricity generation can provide energy and reduce the methane emission. With reference to the methodology based on the Kyoto Protocol mechanisms, this figure represents a potential of over 46,000 megawatt hour (MWh) annually and 800,000 tons of carbon dioxide equivalent (tCO2eq) emission reductions for trading carbon credits

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