Biological wastewater treatment processes (WWTPs), by nature of their reliance on biological entities to
degrade organics and sometimes remove nutrients, are vulnerable to toxicants present in their influent.
Various toxicity measurement methods have been adopted for biologicalWWTPs,but most are performed
off-line, and cannot be adapted to on-line monitoring tools to provide an early warning forWWTPoperators.
However, the past decade has seen a rapid expansion in the research and development of biosensors
that can be used for toxicity assessment of aquatic environments. Some of these biosensors have also been
shown to be effective for use in biological WWTPs. Nevertheless, more research is needed to: examine the
sensitivity of assays and sensors based on single organisms to various toxicants and develop a matrix of
biosensors or a biosensor incorporating multiple organisms that can protect WWTPs; test the micro fuel
cell (MFC)-based biosensors with real wastewaters and correlate the results with the well-established
oxygen uptake rate (OUR)-based or CH4-based toxicity assay; and, develop advanced data processing
methods for interpreting the results of on-line toxicity sensors in real WWTPs to reduce the noise due to
the normal fluctuation in influent quality and quantity.