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 spectrum.