International Journal of Civil and Structural Engineering Research ISSN 2348-7607 (Online) Vol. 7, Issue 1, pp: (129-133), Month: April 2019 - September 2019, Available at: www.researchpublish.com
VS destruction and its impact on VOSC generation under thermophilic and mesophilic anaerobic digestion conditions 1
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Jongmin Kim
Civil Engineering, The University of Texas Rio Grande Valley, Edinburg, Texas, USA
Abstract: Greater organic removal may result in less odorous sludge cake. Thermophilic (55℃) anaerobic digestion (TAD) and mesophilic (37℃) anaerobic digestion (MAD) were tested to understand if greater volatile solids reduction (VSR) could be related to less sulfur-based organic odor or volatile organic sulfur compounds (VOSCs) generation from dewatered and digested sludge. The TAD system removed 10% additional VS than the MAD system, which was reconfirmed by soluble and extractable biopolymer data. The TAD system held more soluble biopolymer than the MAD system while less extractable biopolymer was observed from TAD than MAD. However, greater organic solids removal did not result in lower odor in biopolymer cakes. Hydrogenotrophic methane formers might be responsible for less VOSC removal from thermophilically digested and dewatered sludge. Keywords: Thermophilic anaerobic digestion, mesophilic anaerobic digestion, organic solid reduction, volatile organic sulfur compound.
I. INTRODUCTION Under high temperature (50-60℃) conditions, TADs are able to utilize higher kinetic energy resulting in enhanced solid reduction [15] and better pathogen control than conventional MADs (35-37℃). However, the TAD tends to cause the digestion instability due to high volatile fatty acid production and high ammonia generation due to enhanced protein degradation [8]. Organic sulfur compounds, which are responsible for odors from most dewatered sludge cakes, are generated by complex transformation processes. As described by Higgins et al. [6], volatile organic sulfur compounds (VOSCs) can be produced from anaerobically digested sludge by the degradation of sulfur-containing amino acids such as cysteine and methionine, which can be converted to hydrogen sulfide (H2S) and methanethiol (MT), respectively. Methylation of sulfide and MT by transferring a methyl group from methoxylated aromatic groups like syringate and 3,4,5-trimethoxybenzoate is also suggested as a pathway of MT and Dimethyl sulfide (DMS) generation in anaerobic environments [9]. Dimethyl disulfide (DMDS) can be generated by the oxidation of MT [9]. It has been known that methylotrophic methanogens are responsible for VOSC degradation. Sulfide, methane and carbon dioxide are the final products of mineralization of VOSCs by these methanogens. However, sulfate reducers also have shown anaerobic degradation of MT and DMS [9], [13]. Tanimoto and Bak [13] reported that sulfate reducers from a thermophilic fermenter sludge degraded MT and DMS to carbon dioxide and sulfide with sulfate as an electron acceptor. High sulfide or sulfate environments are likely to stimulate sulfate reducers to outcompete methanogens for VOSC uptake in the freshwater sediments [9]. In this study, two batch anaerobic digestion systems (TAD and MAD) were operated to study their ability to reduce solids and VOSCs. The objectives of this study were; a) To compare the solid reduction efficiencies of the TAD and the MAD; b) To compare the VOSC reduction potentials of the TAD and the MAD; and c) To search for the way to link solid reduction to VOSC generation.
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