Final Effluent & Trade Discharge

UK Legislation

Industrial and municipal waste-water (sewage) treatment plants have had to respond to progressive UK environmental legislation which has culminated in the Waste Water Treatment Directive. Since successive legislation becomes more and more stringent, the need to implement self- monitoring using on-line instrumentation, has become increasingly important to ensure treated effluent is compliant with imposed discharge consents.

Sewage Discharge

Many industrial sites need to treat their effluent to comply with a range of consent parameters that may include pH, suspended solids, ammonia, COD and BOD. Trade discharges to sewer are typically regulated using COD (Chemical Oxygen Demand) and final effluent discharge to the river is typically regulated using BOD (Biological Oxygen Demand). Since both tests are determined in the laboratory on a discrete sample, it has often been necessary for industry to deploy continuous on-line measurement, to proactively manage their discharge and treatment processes. Since a correlation between the Total Organic Carbon content and the associated oxygen demand can often be established, the Protoc TOC analyser technology providing continuous water analysis has been extensively installed to monitor trade discharge and final effluent quality.

Municipal Sewage Discharge

Final effluent monitoring typically comprises ammonia and suspended solids (turbidity) although other water analysis such as BOD may also be performed on discrete samples. Ammonia is a critical water quality parameter since it is toxic to aquatic life and also indicates the extent of treatment. Rising ammonia concentrations indicates inefficient nitrification possibly due to poor aeration, insufficient liquor concentrations, nitrification inhibition due to toxicity, temperature or excessive hydraulic load. Continuous measurement data is therefore crucially important to confirm the treatment facility is operating efficiently.

Recently, the consent limits for discharge have been lowered for sites discharging to sensitive catchments. Consents of 1.0 to 3.0mg/L NH3-N are now more common place requiring analytical measurement technology. The Proam ammonia monitor which provides automatic calibration against two known calibration standards provides a greater confidence in the quality of measurement, especially for sites treating effluent to such low concentrations. More recently, phosphate consents have also been imposed resulting in additional treatment and process control requirements.

Key Water Quality Parameters

• Total Organic Carbon (TOC)
• Ammonia
• pH & Temperature
• Turbidity