title: Modeling and Application of a Rapid Fluorescence-Based Assay for Biotoxicity in Anaerobic Digestion.
abstract: The sensitivity of anaerobic digestion metabolism to a wide range of solutes makes it important to be able to monitor toxicants in the feed to anaerobic digesters to optimize their operation. In this study, a rapid fluorescence measurement technique based on resazurin reduction using a microplate reader was developed and applied for the detection of toxicants and/or inhibitors to digesters. A kinetic model was developed to describe the process of resazurin reduced to resorufin, and eventually to dihydroresorufin under anaerobic conditions. By modeling the assay results of resazurin (0.05, 0.1, 0.2, and 0.4 mM) reduction by a pure facultative anaerobic strain, Enterococcus faecalis, and fresh mixed anaerobic sludge, with or without 10 mg L(-1) spiked pentachlorophenol (PCP), we found it was clear that the pseudo-first-order rate constant for the reduction of resazurin to resorufin, k1, was a good measure of "toxicity". With lower biomass density and the optimal resazurin addition (0.1 mM), the toxicity of 10 mg L(-1) PCP for E. faecalis and fresh anaerobic sludge was detected in 10 min. By using this model, the toxicity differences among seven chlorophenols to E. faecalis and fresh mixed anaerobic sludge were elucidated within 30 min. The toxicity differences determined by this assay were comparable to toxicity sequences of various chlorophenols reported in the literature. These results suggest that the assay developed in this study not only can quickly detect toxicants for anaerobic digestion but also can efficiently detect the toxicity differences among a variety of similar toxicants.
authors.affiliation: Nanyang Environment & Water Research Institute, Advanced Environmental Biotechnology Centre, Nanyang Technological University , Singapore 637141.
authors.forename: Jian Lin
authors.initials: JL
authors.lastname: Chen
authors.affiliation: School of Materials Science & Engineering, College of Engineering, Nanyang Technological University , Singapore 637141.
authors.forename: Terry W J
authors.initials: TW
authors.lastname: Steele
authors.affiliation: Nanyang Environment & Water Research Institute, Advanced Environmental Biotechnology Centre, Nanyang Technological University , Singapore 637141.|Department of Chemical Engineering, Imperial College London , London SW7 2AZ, U.K.
authors.forename: David C
authors.initials: DC
authors.lastname: Stuckey
mesh_terms: D000693:Anaerobiosis; D002733:Chlorophenols / Q000633:toxicity; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000378:metabolism; D005453:Fluorescence; D007202:Indicators and Reagents; D007700:Kinetics; D008962:Models, Theoretical; D010078:Oxazines / Q000737:chemistry; D010084:Oxidation-Reduction; D012722:Sewage / Q000382:microbiology*; D018675:Toxicity Tests; D014966:Xanthenes / Q000737:chemistry
chemical_list: D002733:Chlorophenols; D007202:Indicators and Reagents; D010078:Oxazines; D012722:Sewage; D014966:Xanthenes; C568681:dihydroresorufin; C005843:resazurin; C014180:resorufin