Development of Chemical Oxygen on Demand (COD) Soft Sensor Using Edge Intelligence

The Internet of Things (IoT) based water quality monitoring system, mostly uses cost-effective sensors with a faster response time. Few water quality parameters such as Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Chlorine (Cl), and Total Phosphorous, hard to be measured online, soft sensing techniques are used as an alternate solution to this. This paper studies different Machine Learning (ML) models to prefer a suitable one that can identify the non-linearity of the dependency and establish a correlation between input and output parameters to design a COD soft sensor. The selected models are deployed in the proposed IoT architecture to predict the COD in real-time. More than 16000 data samples from the river Ganga with ten independent water quality parameters are collected and tested to validate the proposed IoT architecture. The paper compares the results of a few best performing ML algorithms like Multiple Linear Regression, Multilayer Perceptron, Support Vector Machine, Random Forest and K-Nearest Neighbour (KNN). Where, KNN technique proves to be the most efficient one in the prediction of COD in terms of response time and other performance matrices like R, R2, MSE, MAE, and RMSE. Finally, the preferred model (KNN) with the IoT setup is deployed and tested at the Sewage Treatment Plant (STP) outlet of the authors' institute to verify the accuracy of the COD in real-time.