Abstract
Humin (HM) has been reported to function as an external electron mediator (EEM) in various microbial reducing reactions. In this study, the effect of isolation methods on EEM functionality and the chemical/electrochemical structures of HM were examined based on the correlation between dechlorination rates in the anaerobic HM-dependent pentachlorophenol (PCP)-dechlorinating consortium and the chemical/electrochemical structures of HM. A lack of PCP dechlorination activity suggested no EEM function in the HM samples prepared as a soluble fraction in dimethyl sulfoxide and sulfuric acid (which did not contain any electric capacitance). Other HM samples exhibited EEM functionality as shown by the dechlorination activity ranging from 0.55 to 3.48 (µmol Cl−) L−1d−1. The comparison of dechlorination activity with chemical structural characteristics suggested that HM with EEM functionalities had predominantly aliphatic and carbohydrate carbons with the partial structures C=O, O=C–N, and O=C–O. EEM functionality positively correlated with the proportion of O=C–N and O=C–O, suggesting an association between peptidoglycan structure and EEM functionality. The lack of detection of a quinone structure in one HM sample with EEM functionality and a negative correlation with aromatic or C=C carbon suggested that the mechanism containing quinone structures is a minor component for the functionality of EEM.
Highlights
The function of humic substances (HSs) as external electron mediators (EEM) in soil and sediment was found to reduce iron during microbial respiration by Lovely et al [1]
The different isolation methods resulted in different electron mediating abilities of the HMs, even if they were obtained from the same soil, as shown by the dechlorination rates ranging from 0.55 to 3.48 L−1 d−1, except for HM-M7 (Table 2)
Seven HM samples were isolated using different methods. These HMs were examined for EEM functionality using the anaerobic HM-dependent PCP-dechlorinating consortium
Summary
The function of humic substances (HSs) as external electron mediators (EEM) in soil and sediment was found to reduce iron during microbial respiration by Lovely et al [1]. This redox-active property of HSs has been studied extensively during the past two decades, but all of the studies focused on soluble fractions of HSs [2,3,4,5]. The function of HM as EEM has been explored, including that in the debromination of tetrabromobisphenol A [9] and iron and nitrate reduction [10] This electroactive function of HM has been successfully further applied to a bioelectrochemical remediation system for the dechlorination of PCP [11] and for nitrate
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
