Online Water Quality Control: the "EarlyWarning" System
The WPR system is a soft computing application for online/early warning monitoring of wastewater quality and the WPR indicator trend, based on conventional online measurements in channels and at plant inlet/outlet points.
Operating Principle
The WPR (Water Pollution Rate) index is inspired by the better-known WQI (Water Quality Index), developed in 1970 by approximately one hundred water quality experts from the EPA and NSF. The WQI measures water quality changes in specific river sections and enables comparison across different rivers.
The system tracks online water samples using WPR on a two-dimensional XY control plane where: the Y-axis (WQI) represents water quality based on estimated pollutant load; the X-axis represents complementary quality factors such as treatability at plant inlet or regulatory compliance at outlet against reference limits.
WPR System Components
- Online analytical instrumentation for water quality parameters (pH, redox, dissolved oxygen, temperature, electrical conductivity, turbidity, flow rate, etc.)
- PLC/PC control unit for signal processing connected to SCADA telemetry networks
- Functional installation and operation accessories
Three Foundational Principles
First Principle: Within known water classes, among natural or semi-natural water quality parameters exists a subset of values where exceeding limits in some parameters indicates exceedance in others.
Second Principle: The NSF-WQI, developed by the National Sanitation Foundation in 1970, applies to natural waters with corrections introducing a Complementary Quality Index. For wastewater, the WPR index derived from appropriate knowledge bases enables online multi-clustering measurement.
Third Principle: These principles enable identification of a minimum acceptable reference quality level against which to measure deviations in inlet and outlet water quality.
Parameter Measurement
The index can be evaluated via online detection of nine parameters (eight chemical, one bacteriological): BOD₅, dissolved oxygen, pH, temperature, total dissolved solids, turbidity, total nitrogen, total phosphorus, and fecal coliforms.
WPR Formulas
For raw wastewater (plant inlet):
WPR_in = Fuzzy [ORP, pH, T, EC, NTU, LV, Q]
For treated wastewater (plant outlet):
WPR_out = Fuzzy [ORP, NTU, Q]
Primary Operational Functions
- Graphical and numerical display of water quality index values
- Continuous comparison between quality indices and reference limits
- Pre-alarm (early warning) and alarm signaling for continued limit exceedance
- Data archiving and historical management
- WPR system guidance and troubleshooting