Electro-active biofilms (EABfs) can be studied using several visual techniques.

Non-destructive techniques can be used for online biofilm monitoring.

Visualization of EABfs allows for monitoring growth and analyzing cell components.

We show what information on EABfs the different visual techniques can yield.

The advantages and challenges of each technique are discussed.

Optimization of bio-electrochemical systems (BESs) relies on a better understanding of electro-active biofilms (EABfs). These microbial communities are studied with a range of techniques, including electrochemical, visual and chemical techniques. Even though each of these techniques provides very valuable and wide-ranging information about EABfs, such as performance, morphology and biofilm composition, they are often destructive. Therefore, the information obtained from EABfs development and characterization studies are limited to a single characterization of EABfs and often limited to one time point that determines the end of the experiment. Despite being scarcer and not as commonly reported as destructive techniques, non-destructive visual techniques can be used to supplement EABfs characterization by adding in-situ information of EABfs functioning and its development throughout time. This opens the door to EABfs monitoring studies that can complement the information obtained with destructive techniques. In this review, we provide an overview of visual techniques and discuss the opportunities for combination with the established electrochemical techniques to study EABfs. By providing an overview of suitable visual techniques and discussing practical examples of combination of visual with electrochemical methods, this review aims at serving as a source of inspiration for future studies in the field of BESs.

Electro-active biofilms

Electrochemical techniques

Visual techniques

Destructive

In-situ

© 2022 The Author(s). Published by Elsevier Inc.