Miniaturized solid-state sensor for inline monitoring of the microbial biodegradation of a biohazardous textile azo dye (Direct Red-81)

Microbial biodegradation employs non-hazardous microbes to detoxify or eliminate toxic chemicals. Direct Red-81 (DR81) is a toxic and carcinogenic dye discharged in textile-industry wastewater and contaminates water resources. The offline spectrophotometric methods commonly used to monitor biodegradation require sampling and sample preparation. They do not consider the change in the medium composition and the generated products that may perturb the method selectivity. Potentiometric sensors introduce a simple direct, inline, portable, and real-time analysis tool. To our knowledge, no potentiometric sensor was reported for online monitoring of an ongoing microbial-biodegradation process. Recent work reports the biodegradation of DR81 using Candida albicans, where the researchers withdrew samples frequently to monitor the change in the UV–visible spectrum of DR81. This study optimizes and validates a portable and selective solid-state potentiometric sensor to monitor the microbial biodegradation of DR81 in the dilute mineral salt medium. The optimized sensor composition includes 1.61% tetra-dodecyl ammonium chloride, 66.47% dioctyl phthalate, 1.61% Calix-[4]-arene and 30.31% polyvinyl chloride matrix. The sensor results conform with our previous work results; however, the portable sensor monitored the ongoing microbial degradation inline without sampling and in real-time. The sensor assists microbiologists and environmentalists in comprehending the process and optimizing the conditions for DR81 microbial biodegradation.