Underwater spectrophotometer for in-situ seawater COD monitoring

Traditional seawater chemical oxygen demand (COD) monitoring methods are based on manual operations, which require various operating procedures and long duration of measurement, are prone to secondary pollution and hence unsuitable for in-situ monitoring. In this paper, we developed a prototype of in-situ seawater COD monitoring sensor based on UV-Vis absorption spectroscopy, and integrating it to a buoy for coastal trials. During the trials, several measures were applied to reduce the influence of biofouling, including coating sensor housing with an environment-friendly anti-fouling paint, and designing a motorized underwater wiper for optical window cleaning. The in-situ COD sensor had been continuously working underwater for more than 6 months, obtaining 1536 sets of seawater UV-Vis absorption sectrum.