Single-wavelength colorimetric tests for low-cost estimation of bacterial activity, chemical oxygen demand, and turbidity in domestic wastewater

Abstract Monitoring the characteristics of wastewater can enable a better choice of the options available for its treatment and also provide a rational basis for the surveillance of the spread of waterborne diseases. Our work focused on bringing down the costs associated with the estimation of the biological and physico-chemical parameters of wastewater at a common wavelength of 600 nm. We demonstrated the advantages of using the Dye Reduction-based Electron-transfer Activity Monitoring (DREAM) assay to estimate bacterial activity as an alternative to the bacterial colony count method. This assay relies on the colorimetric measurement of the extent of reduction of methylene blue in response to bacterial electron transfer. We also present the results of estimating COD and turbidity, using the standard methods of wastewater analysis, at the same wavelength of 600 nm using samples having known values of chemical oxygen demand (COD) and turbidity. Our results open up the possibility of replacing expensive spectrophotometers with LED-based, microcontroller enabled colorimeters that can be easily automated. The results of our study set the stage for the establishment of a greater number of wastewater analysis laboratories in economically backward regions which can in turn support measures to improve sanitation facilities.