Paper sensor-based method using a portable 3D-printed platform and smartphone-assisted colorimetric detection for ammonia and sulfide monitoring in anaerobic digesters and wastewater

Abstract

A simple and low-cost field-deployable method using paper sensors in combination with a 3D-printed portable platform to simultaneous determination of ammonia and sulfide has been developed. Ammonia and sulfide are harmful pollutants for the environment and important toxicants inhibiting anaerobic digestion, therefore, are key monitoring parameters during wastewater treatment. The sample preparation system consisted of a well microplate and sensor paper discs placed inside the microplate sealing system. Gas pervaporation and diffusion of ammonia and hydrogen sulfide across a Teflon membrane onto a paper discs, impregnated with bromothymol blue and methylene blue assay reagents, allowed the ammonia and sulfide determination, respectively. The detection system consisted in a 3D-printed photographic lightbox with LED plates and a smartphone. A code was developed in ImageJ for a fast colorimetric measurement of the digital images. Under optimal conditions, limits of detection of 1.3 and 1.7 mg L-1 and linear concentration ranges between 5 and 50 mg L-1 and 5–45 mg L-1, were obtained for ammonia and sulfide, respectively. The analysis of an anaerobic digester and wastewater samples revealed good precisions (RSDs < 10 %) and recoveries (91–105 %). This methodology shows advantages such as a high precision, a simple paper discs preparation and a reusable system.