Early warning of changing drinking water quality by trend analysis Jani Tomperi, Esko Juuso and Kauko Leiviskä ABSTRACT Monitoring and control of water treatment plants play an essential role in ensuring high quality drinking water and avoiding health-related problems or economic losses. The most common quality variables, which can be used also for assessing the efficiency of the water treatment process, are turbidity and residual levels of coagulation and disinfection chemicals. In the present study, the trend indices are developed from scaled measurements to detect warning signs of changes in the quality variables of drinking water and some operating condition variables that strongly affect water quality. The scaling is based on monotonically increasing nonlinear functions, which are generated with generalized norms and moments. Triangular episodes are classified with the trend index and its derivative. Deviation indices are used to assess the severity of situations. The study shows the potential of the described trend analysis as a predictive monitoring tool, as it provides an advantage over the traditional manual inspection of variables by detecting changes in water quality and giving early warnings. Jani Tomperi (corresponding author) Esko Juuso Kauko Leiviskä Control Engineering, Faculty of Technology, University of Oulu, PO Box 4300, FIN-90014 University of Oulu, Oulu, Finland E-mail: jani.tomperi@oulu.fi Key words | aluminium, drinking water, nonlinear scaling, operating conditions, turbidity, water treatment process INTRODUCTION There is a growing demand to improve water treatment man- agement to ensure high quality water for consumers at as low as possible operating cost. Efficient monitoring and con- trol have a key role in high quality drinking water processing at water treatment plants (WTPs). Many process measure- ments are available in modern WTPs, but the quality of the processed water is not measured until it is leaving the plant for distribution to consumers and corrective control actions have no effect on water quality. In addition, water treatment processes are very challenging for monitoring, modelling and control because they are complex, nonlinear processes where several (partly unknown) variables affect the functionality and quality of water. Poorly operating WTPs and low quality water may cause health problems to consumers and significant economic losses to a WTP. Health effects can be due to single exposures to microbial pathogens or long-term exposure to chemicals. Economic losses include excessive chemical and energy consumption, cleaning the distribution system, compensation to consu- mers and process improvements. The contamination of the water can be prevented, reduced or eliminated by the proper control of the process. Successful control, on the other hand, requires accurate monitoring of the process. Specific limits of the operating and quality variables are monitored by on-line or laboratory analysis (WHO (World Health Organization) , ). The quality of drinking water and the efficiency of a WTP can be assessed by many parameters, but the most common are turbidity and residual chemical level. Surface waters are typically treated by a chemical coagulation- based process, and aluminium or iron salts are widely used as coagulants to reduce the organic matter, colour and turbidity of raw water (WHO (World Health Organiz- ation) ). Aluminium has a good ability to coagulate 433 © IWA Publishing 2016 Journal of Water and Health | 14.3 | 2016 doi: 10.2166/wh.2016.330 Downloaded from https://iwaponline.com/jwh/article-pdf/14/3/433/394303/jwh0140433.pdf by guest on 21 December 2018