LAUSR

in Activated Carbon Facilitate Microbial Reduction of Ferrihydrite” A recently published paper investigated microbial ferrihydrite reduction in the presence of modified activated carbon (AC) with different types and quantities of surfaceoxygen groups. Although we greatly appreciate this work, we would like to point out some apparent contradictions in the interpretation of the results. Resolving the herein outlined comments is both scientifically valuable and of relevance to possible applications of activated carbon in redox-mediated reactions. Redox-active surface functional groups on activated carbon induces reducing and oxidizing capacities. If properly understood and used, such activated carbons with redox capacities could be deployed to shuttle electrons from microbial metabolism to the environment for example in applications such as degradation of chlorinated contaminants and of azo dyes.