Abstract
Quinones and humus are ubiquitous in the biosphere and play an important role in the anaerobic biodegradation and biotransformation of organic acids, poisonous compounds as well as inorganic compounds. The impact of humic model compound, anthraquinone-2, 6-disulfonate (AQDS) on anaerobic phenol and p-cresol degradation were studied. Four methanogenic AQDS-free phenol and p-cresol enrichments and two phenol-AQDS enrichments were obtained using two sludges with potential biodegradability of phenol and cresol isomers as inoculum. 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that syntrophic aromatic compound degrading bacterium Syntrophorhabdus aromaticivorans was dominant in four AQDS-free enrichments, whereas phenol degrading Cryptanaerobacter phenolicus was dominant in two phenol-AQDS enrichments. Neither co-culture of S. aromaticivorans with Methanospirillum hungatei nor two phenol-AQDS enrichments could metabolize phenol using AQDS as the terminal electron acceptor. Further degradation experiments suggested that C. phenolicus related microbes in two phenol-AQDS enrichments were responsible for the conversion of phenol to benzoate, and benzoate was further degraded by benzoate degraders of Syntrophus aciditrophicus or Sporotomaculum syntrophicum to acetate.
Highlights
Phenol and cresol isomers are important petrochemical products and commonly found in wastewaters from coal gasification, petrochemical manufacturing, oil-refining, synthetic chemicals, pesticides, and pharmaceuticals industries
We reported the impact of AQDS on phenol and p-cresol degradation by enrichment cultures
Microorganisms and cultivation Methanogenic sludges were taken from two lab-scale, mesophilic (35 °C), upflow anaerobic sludge blanket (UASB) reactors: (i) sludge C treated cresols for one year; (ii) sludge N treated nitro-phenol for three months (Zhang et al 2005)
Summary
Phenol and cresol isomers (ortho-, meta-, and para-cresols) are important petrochemical products and commonly found in wastewaters from coal gasification, petrochemical manufacturing, oil-refining, synthetic chemicals, pesticides, and pharmaceuticals industries. Phenols are found in municipal landfill leachates, lignin residues in anaerobic agroecosystems, and methanogenic bioreactors treating organic solid wastes, such as slaughter house waste, animal manure, food wastes and crop residues (Levén et al 2012; Qiao et al 2013). Studying anaerobic degradation of phenols is necessary to the industrial wastewater treatment processes and the biogeochemical process of natural phenols. The oxidation of phenol to acetate, carbon dioxide, and hydrogen is unfavorable, and phenol is thought to be metabolized only at a very low hydrogen partial pressure. Phenol degradation requires the coupling of fermentative bacteria with methanogens to overcome thermodynamics limit. C6H6O þ 6.5H2O → 3.5CH4 þ 2.5HCO3À þ 2.5Hþ (ΔG0’ 1⁄4 À155.3 kJ reactionÀ1); C7H8O þ 7.5H2O → 4.25CH4 þ 2.75HCO3À þ 2.75Hþ (ΔG0’ 1⁄4 À 187.5 kJ reactionÀ1) (Cervantes et al 2000a)
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