Increasing untreated environmental outputs from industry and the rising human population have increased the burden of wastewater and other waste streams on the environment. The most prevalent wastewater treatment methods include the activated sludge process, which requires aeration and is, therefore, energy and cost-intensive. The current trend towards a circular economy facilitates the recovery of waste materials as a resource. Along with the amount, the complexity of wastewater is increasing day by day. Therefore, wastewater treatment processes must be transformed into cost-effective and sustainable methods. Microbial fuel cells (MFCs) use electroactive microbes to extract chemical energy from waste organic molecules to generate electricity via waste treatment. This review focuses use of MFCs as an energy converter using wastewater from various sources. The different substrate sources that are evaluated include industrial, agricultural, domestic, and pharmaceutical types. The article also highlights the effect of operational parameters such as organic load, pH, current, and concentration on the MFC output. The article also covers MFC functioning with respect to the substrate, and the associated performance parameters, such as power generation and wastewater treatment matrices, are given. The review also illustrates the success stories of various MFC configurations. We emphasize the significant measures required to fill in the gaps related to the effect of substrate type on different MFC configurations, identification of microbes for use as biocatalysts, and development of biocathodes for the further improvement of the system. Finally, we shortlisted the best performing substrates based on the maximum current and power, Coulombic efficiency, and chemical oxygen demand removal upon the treatment of substrates in MFCs. This information will guide industries that wish to use MFC technology to treat generated effluent from various processes.

A comprehensive review of the current state of microfluidic bioanalytical research applied to bacterial biofilms.

A microfluidic platform with a fluorescent nanoparticle-based sensor is demonstrated for real-time, ratiometric pH imaging of biofilms. Sensing is accomplished by a thin patterned layer of covalently bonded Ag@SiO₂+FiTC nanoparticles on an embedded planar glass substrate. The system is designed to be sensitive, responsive and give sufficient spatial resolution to enable new micro-scale studies of the dynamic response of oral biofilms to well-controlled chemical and hydrodynamic stimulation. Performance under challenging operational conditions is demonstrated, which include long-duration exposure to sheer stresses, photoexcitation and pH sensor biofouling. After comprehensive validation, the device was used to monitor pH changes at the attachment surface of a biofilm of the oral bacteria, Streptococcus salivarius. By controlling flow and chemical concentration conditions in the microchannel, biochemical and mass transport contributions to the Stephan curve could be probed individually. This opens the way for the analysis of separate contributions to dental caries due to localized acidification directly at the biofilm tooth interface.