Activated Carbon as an Electron Acceptor and Redox Mediator during the Anaerobic Biotransformation of Azo Dyes

Abstract

Activated carbon (AC) has a long history of applications in environmental technology as an adsorbent of pollutants for the purification of drinking waters and wastewaters. Here we describe novel role of AC as redox mediator in accelerating the reductive transformation of pollutants as well as a terminal electron acceptor in the biological oxidation of an organic substrate. This study explores the use of AC as an immobilized redox mediator for the reduction of a recalcitrant azo dye (hydrolyzed Reactive Red 2) in laboratory-scale anaerobic bioreactors, using volatile fatty acids as electron donor. The incorporation of AC in the sludge bed greatly improved dye removal and formation of aniline, a dye reduction product. These results indicate that AC acts as a redox mediator. In supporting batch experiments, bacteria were shown to oxidize acetate at the expense of reducing AC. Furthermore, AC greatly accelerated the chemical reduction of an azo dye by sulfide. The results taken as a whole clearly suggest that AC accepts electrons from the microbial oxidation of organic acids and transfers the electrons to azo dyes, accelerating their reduction. A possible role of quinone surface groups in the catalysis is discussed.

Biochar‐mediated reductive transformation of nitro herbicides and explosives

“…A second possibility involves redox-labile surface functional groups, such as (hydro)quinone. Quinone moieties have been suggested to catalyze the reduction of nitro and azo compounds [25,33]. In contrast to high-purity graphite, both poultry litter and biosolids biochars contained a substantial amount of oxygen, as shown in Table 2.…”

Preparation characteristics and accelerating denitrification effectiveness of polyamide 6 modified by AQS

“…A redox mediator, for example, the quinone redox mediator, serves as an electron donor to accelerate the microbial reduction. [18] New functional polymer biocarriers are conducive to microorganism growth on the surface and accelerate the biotransformation of contaminants. However, the reported functional polymer biocarriers were not ideal for application and this is why novel functional polymer biocarriers need to be explored.…”

Mechanism of enhanced nitrate reduction via micro-electrolysis at the powdered zero-valent iron/activated carbon interface

“…AC could thus enhance reduction efficiency by transferring electrons from galvanic corrosion of iron to the contaminant [23]. Under anaerobic conditions, organic pollutants are also significantly reduced by atomic hydrogen and Fe(II) released from the micro-electrolysis process [24].…”