Development of a portable, microwell-based, smartphone-assisted colorimetric device to measure the activities of anaerobic digestion

Anaerobic digestion (AD) is a complex process that can be severely impacted by a range of toxicants found in wastewater, leading to system failure. To prevent this, monitoring key process indicators is crucial, but current methods have limitations in terms of response time and reliability. To address this challenge, we propose an innovative solution for ex situ monitoring of biotoxicity in AD using a paper-microwell-based and smartphone-assisted colorimetric analytical device. This device utilizes resazurin reduction by anaerobic sludge as a biological indicator, which reflects the health of anaerobic microbial consortia with a short response time. The device is fabricated through plasma treatment of chromatography paper, integrated with resazurin, and requires no external power source. To evaluate the device's efficiency, we conducted tests to measure and differentiate the toxicity of three types of chlorophenols, namely pentachlorophenol, 2,4-dichlorophenol, and 4-chlorophenol, after loading them into AD for a duration of 30 min. This paper-microwell-based analytical device demonstrated its ability to identify the presence of toxicants and provide a quick response time, making it a promising technology for monitoring toxicity incidents in real-time in AD processes. With its low cost, portability, and reliability, this innovative technology has the potential to contribute to the prevention of system failure caused by toxicants in AD processes. The analytical greenness metric approach (AGREE) proposes this paper-based analytical device as a greener alternative for measuring anaerobic digestion activities compared to traditional methods such as biochemical methane potential and chemical oxygen demand.