Pattern Overview

This pattern applies to municipal and industrial wastewater treatment plants where effluent quality parameters (COD, BOD, TSS, ammonia) must be monitored for regulatory compliance but are measured only through laboratory analysis with a 24–48 hour turnaround. The soft sensor provides continuous 5-minute estimates from instrumentation that is typically already installed in the plant (flow meters, pH probes, DO sensors, turbidity meters).

When to Use This Pattern

• The plant operates under consent-based discharge limits with regulatory monitoring obligations.
• Laboratory analysis costs and delays are a bottleneck for operational decision-making.
• Online analysers for COD or TSS are cost-prohibitive or require reagent replenishment that is operationally burdensome.
• Aeration or chemical dosing optimization is desired but currently limited by slow quality feedback.

Deployment Considerations

The LSTM model requires a minimum of 6–12 months of concurrent lab results and continuous sensor data for initial training. Data quality is critical: sensor drift and calibration gaps in the training data directly degrade model performance. A CUSUM-based drift detector monitors the distribution of input features and flags when the model should be retrained — typically triggered by seasonal transitions, significant influent composition changes (e.g., industrial discharge permit changes), or sensor replacement events.

The Random Forest backup model provides interpretability for operator trust: feature importance scores show which sensor inputs drive each prediction, allowing operators to validate model behaviour against process intuition.