Feasibility of using in situ UV/Vis spectrometer probe for measuring COD in WWTP based on UASB reactor

Abstract

The aim of this work is to report the use of a UV/Vis spectrometer for real time, in situ monitoring of the chemical oxygen demand (COD) in a municipal wastewater treatment plant (WWTP) operating with upflow anaerobic sludge blanket (UASB) reactor, installed in south of Brazil. The spectrometer was used according to the factory calibration procedures: global, local offset and local linear. COD probe measurements were compared to laboratory analyses for the calibration procedures. Continuous operation led to increasing errors, which was related to grime deposition on the probe window and avoided with periodic cleaning. Performance of the probe measurements versus laboratory analyses was evaluated with coefficient of determination, root mean squared error (RMSE), relative RMSE, RMSE to standard deviation ratio (RSR) and Student’s t-test. It is concluded that the best calibration procedures is the local linear, for the influent and the effluent of UASB reactor. The probe consists of an improvement to real time and in situ monitoring of South America WWTPs.